Thermal Power Sensors (C-Series)

Power Ranges Covering 10 µW to 200 W
Wavelength Ranges Covering 190 nm to 20 µm
Broadband Coatings with High Damage Thresholds
Sensors Designed for Microscopes and Pulsed Lasers

S425C-L

Featuring Removable
Heat Sink and Shown
with a Fiber Adapter
(Sold Below) and
Fiber Patch Cable

S350C

For Excimer Lasers

S401C

High Sensitivity
Down to 10 µW

S175C

18 mm x 18 mm Aperture Size
for Use with Microscopes

Please Wait

Overview
Specs
Pin Diagrams
Operation
Console Selection
Pulse Calculations
Sensor Selection
Feedback

Click to Enlarge

Internal SM05 (0.535"-40) threading on the S405C's aperture (left) accepts the included external SM05 to SM1 (1.035"-40) thread adapter (right). Most sensors include an SM1 externally threaded adapter that allows accessories like fiber adapters to be mounted.

Click to Enlarge
S401C Connected to the PM100D Console

Power Meter Selection Guide
Sensors
Photodiode Power Sensors
Thermal Power Sensors
Thermal Position & Power Sensors
Pyroelectric Energy Sensors
Power Meter Consoles
Digital Handheld Console
Analog Handheld Console
Touchscreen Handheld Console
Dual-Channel Benchtop Console
Complete Power Meters
Power Meter Bundles
Wireless Power Meters with Sensors
Compact USB Power Meters
Field Power Meters for Terminated Fibers
USB Interfaces, External Readout

Features

Broad Spectral Ranges with Relatively Flat Spectral Responses (See Plots Below)
Individually Calibrated with NIST- and PTB-Traceable Certificate of Calibration
Free-Space and Fiber-Based Applications Supported
- All Sensors Accept Free Space Input
- Majority Accept Fiber Adapter (Available Below) for Fiber-Based Input
C-Series Connector
- Enables Quick Sensor Connection to Our Power Meter Consoles
- Embedded EEPROM Contains Sensor and Calibration Data
Ten Models Feature Over-Temperature-Alert Sensor (See Specs Tab for Details)

Thorlabs' C-Series Thermal Power Sensors are collectively able to detect power ranges from 10 µW to 200 W and wavelength ranges from 190 nm to 20 µm. These thermopile-based sensors are ideal choices for measuring broadband spectra from amplified spontaneous emission (ASE) sources, light emitting diodes (LEDs), filament lamps, swept-wavelength lasers, and other sources. In addition, thermal power sensors do not saturate, which makes them well suited to measuring pulsed sources with high pulse peak powers or long-duration pulses. These thermal power sensors also exhibit low dependency on the angle and position of the incident light beam. They are preferred for applications that cannot tolerate the strong wavelength dependencies and/or saturation thresholds of photodiode sensors. However, thermal power sensors generally have lower power resolutions and longer response times. We offer a wide range of thermal power sensors, with each including different design features.

Mounting
The sensors sold here (except the S175C) can be mounted on our Ø1/2" Posts using an 8-32, M4, or M6 tap. A 60 mm or 75 mm tall post is included with select sensors. Additionally, many of our thermal sensors are compatible with 30 mm cage systems, Ø1" lens tube systems, and our fiber adapters (sold below). Please refer to the Specs tab for more information.

Calibration
Each sensor head is individually calibrated and is shipped with a NIST- and PTB-Traceable Calibration Certificate. The calibration and identification data is stored in the electrically erasable programmable read-only memory (EEPROM) built into the connector of the sensor and is downloaded automatically to the connected power meter console. The EEPROM also contains sensor model and serial numbers, wavelength range, information on the built-in thermistor (when present), and the calibration date. For more information on sensor calibration, please see the Calibration tab on our Power Meter and Sensor Tutorial.

Power Meter Compatibility
All sensors are connected to the power meter console via the C-Series connector, which offers quick sensor exchange. These sensors are compatible with our current power meter console offering but cannot be used with our previous generation of consoles. For our sensors with natural response times greater than 1 second, these power meters can use the data stored in the connector to predict the incident power after a single time constant of the sensor. Please see the Operation tab for more information.

Recalibration Services
Thorlabs offers recalibration services for our thermal power sensors. To ensure accurate measurements, we recommend recalibrating the sensors annually. This service can be ordered below (see Item # CAL-S200).

Sensor Upgrade and Service
All C-Series Sensors are incompatible with former generation power meter consoles with non-C-Series connectors. We offer a sensor upgrade service if you want to use your existing sensors with a new power meter console with a C-Series connector. Note: upgraded sensors will be incompatible with old power meter consoles with non-C-Series connectors. Please contact our Tech Support team for details.

Thermal Power Sensors Quick Links
Type	High Resolution	Max Power: 10 W	Max Power: 40 W to 200 W	High Max Power Density for Pulsed Lasers	Microscope Slide Thermal Sensor
Wavelength Range^a	190 nm - 20 µm	190 nm - 20 µm	190 nm - 20 µm	250 nm - 10.6 µm	300 nm - 10.6 µm
Optical Power Range^a	10 µW - 5 W	2 mW - 10 W	10 mW - 200 W	100 µW - 10 W	100 µW - 2 W
Max Optical Power Density^a	500 - 1500 W/cm² (Avg.)	1500 W/cm² (Avg.)	2 - 4 kW/cm² (Avg.)	35 W/cm² (Avg.); 100 GW/cm² (Peak, 1 ns Pulse)	200 W/cm²
Resolution^a	1 µW - 5 µW	100 µW	100 µW - 5 mW	10 µW - 250 µW	10 µW

Combined Range for All Sensors in the Respective Category

Thorlabs' Thermal Power Sensors (C-Series)

Click on the links in the following list or Selection Guide to move to the indicated specification tables.

High Resolution
Max Power: 10 W
Max Power: 40 W to 200 W
High Max Power Density for Pulsed Lasers
Microscope Slide Thermal Sensor

High Resolution

Item #	S401C	S405C
Detection Specifications
Detector Type	Thermal Surface Absorber with Background Compensation (Axial Thermopile)	Thermal Surface Absorber (Axial Thermopile)
Wavelength Range	190 nm - 20 µm	190 nm - 20 µm
Optical Power Range	10 µW - 1 W	100 µW - 5 W
Max Average Power Density^a	500 W/cm²	1.5 kW/cm²
Max Pulse Energy Density	0.2 J/cm² (1 µs Pulse), 2 J/cm² (1 ms Pulse)	0.3 J/cm² (1 ns Pulse), 5 J/cm² (1 ms Pulse)
Max Intermittent Power^b	3 W	-
Linearity	±0.5%	±0.5%
Resolution^c	1 µW	5 µW
Measurement Uncertainty^d (Calibration Uncertainty)	±3% @ 1064 nm ±5% @ 190 nm - 10.6 µm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm
Response Time^e	1.1 s	1.1 s
General Information
Suggested Application	Low Power Lasers and LEDs	Low Power Lasers and LEDs
Absorber	High-Power Broadband Coating	High-Power Broadband Coating
Cooling	Convection (Passive)
Temperature Sensor (In Sensor Head)	NTC Thermistor	NTC Thermistor
Console Compatibility	PM400, PM100D, PM100A, PM320E, and PM100USB
Mechanical Specs
Housing Dimensions (Without Adapter)	33.0 m x 43.0 mm x 15.0 mm (1.30" x 1.69" x 0.59")	40.6 mm x 40.6 mm x 16.0 mm (1.60" x 1.60" x 0.63")
Sensor Input Aperture	Ø10 mm	Ø10 mm
Active Detector Area	10 mm x 10 mm	10 mm x 10 mm
Distance to Detector^f	3 mm	5 mm
Cable Length	1.5 m
Connector	D-Sub 9 Pin Male
Weight	0.05 kg (0.11 lb)	0.11 kg (0.24 lb)
Mounting and Accessories
Post	Ø1/2" Post via Universal 8-32 & M4 Tap (Post Not Included)	Ø1/2" Post via Universal 8-32 & M4 Tap (Post Not Included)
Cage System Mounting	N/A	30 mm Cage Systems via Two 4-40 Tapped Holes; Two Ø6 mm Through Holes for ER Series Rods
Aperture Thread	Externally SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters	Internally SM05-Threaded Aperture Externally SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters
Fiber Adapters (Available Below)	S120 Series Fiber Adapters

For continuous wave (CW) sources, this value is equivalent to the peak power density, while for pulsed laser sources this value is calculated from the time-averaged power and beam profile.
Twenty-minute maximum exposure time for the S401C. The S405C saturates for optical input powers >5 W.
Measurement taken with the legacy PM200 console for the S401C and the PM400 console for the S405C. In both cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). See the Operation tab for additional information.
Distance is measured from the detector to the front face of the housing.

Max Power: 10 W

Item #	S415C	S425C
Detection Specifications
Detector Type	Thermal Surface Absorber (Axial Thermopile)	Thermal Surface Absorber (Axial Thermopile)
Wavelength Range	190 nm - 20 µm	190 nm - 20 µm
Optical Power Range	2 mW - 10 W	2 mW - 10 W
Max Average Power Density^a	1.5 kW/cm²	1.5 kW/cm²
Max Pulse Energy Density	0.3 J/cm² (1 ns Pulse), 5 J/cm² (1 ms Pulse)	0.3 J/cm² (1 ns Pulse), 5 J/cm² (1 ms Pulse)
Max Intermittent Power^b	20 W	20 W
Linearity	±0.5%	±0.5%
Resolution^c	100 µW	100 µW
Measurement Uncertainty^d (Calibration Uncertainty)	±3% @ 1064 nm ±5% @ 250 nm - 17 µm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm
Response Time^e	0.6 s	0.6 s
General Information
Suggested Application	Low and Mid-Power Lasers & LEDs	Low and Mid-Power Lasers & LEDs
Absorber	High-Power Broadband Coating	High-Power Broadband Coating
Cooling	Convection (Passive)
Temperature Sensor (In Sensor Head)	NTC Thermistor
Console Compatibility	PM400, PM100D, PM100A, PM320E, and PM100USB
Mechanical Specs
Housing Dimensions (Without Adapter)	50.8 mm x 50.8 mm x 35.0 mm (2.00" x 2.00" x 1.38")	50.8 mm x 50.8 mm x 35.0 mm (2.00" x 2.00" x 1.38")
Sensor Input Aperture	Ø15 mm	Ø25.4 mm
Active Detector Area	Ø15 mm	Ø27 mm
Distance to Detector^f	5 mm	4.6 mm
Cable Length	1.5 m
Connector	D-Sub 9-Pin Male
Weight	0.22 kg (0.49 lb)	0.22 kg (0.49 lb)
Mounting and Accessories
Post	Ø1/2" Post via Universal 8-32 & M4 Tap (Post Not Included)	Ø1/2" Post via Universal 8-32 & M4 Tap (Post Not Included)
Cage System Mounting	N/A	N/A
Aperture Thread	Internally SM1-Threaded Aperture External SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters	Internally SM1-Threaded (1.035"-40) with External SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters
Fiber Adapters (Available Below)	S120 Series Fiber Adapters

For continuous wave (CW) sources, this value is equivalent to the peak power density, while for pulsed laser sources this value is calculated from the time-averaged power and beam profile.
Two Minute Maximum Exposure Time
Measurement taken with the PM400 with the acceleration circuit switched off. Resolution performance will be similar with our other power meter consoles.
Measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). As the natural response times of the S415C and S425C are fast, these do not benefit from accelerated measurements and this function cannot be enabled. See the Operation tab for additional information.
Distance is measured from the detector to the front face of the housing.

Max Power: 40 W to 200 W

Item #	S350C	S425C-L	S322C
Detection Specifications
Detector Type	Thermal Surface Absorber (Radial Thermopile)	Thermal Surface Absorber (Axial Thermopile)	Thermal Surface Absorber (Radial Thermopile)
Wavelength Range	190 nm - 1.1 µm, 10.6 µm	190 nm - 20 µm	250 nm - 11 µm
Optical Power Range	10 mW - 40 W	2 mW - 50 W	100 mW - 200 W
Max Average Power Density^a	2 kW/cm²	1.5 kW/cm²	4 kW/cm²
Max Pulse Energy Density	0.7 J/cm² (1 ns Pulse), 10 J/cm² (1 ms Pulse)	0.3 J/cm² (1 ns Pulse), 5 J/cm² (1 ms Pulse)	0.5 J/cm² (1 ns Pulse), 10 J/cm² (1 ms Pulse)
Max Intermittent Power^b (2 Minute Max)	60 W	75 W	250 W
Linearity	±1%	±0.5%	±1%
Resolution^c	1 mW	100 µW	5 mW
Measurement Uncertainty^d (Calibration Uncertainty)	±3% @ 351 nm ±5% @ 190 nm - 1100 nm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm	±3% @ 1064 nm ±5% @ 266 nm - 1064 nm
Response Time^e	9 s (1 s from 0 to 90%)	0.6 s	5 s (1 s from 0 to 90%)
General Information
Suggested Application	High Power Excimer Lasers	Mid-Power Lasers	Mid-Power Lasers
Absorber	Excimer Coating	High-Power Broadband Coating	High-Power Broadband Coating
Cooling	Convection (Passive)		Forced Air with Fan^ef
Temperature Sensor (In Sensor Head)	NTC Thermistor
Console Compatibility	PM400, PM100D, PM100A, PM320E, and PM100USB
Mechanical Specs
Housing Dimensions (Without Adapter, if Applicable)	100 mm x 100 mm x 54.2 mm (3.94" x 3.94" x 2.13")	100.0 mm x 100.0 mm x 58.0 mm (3.94" x 3.94" x 2.28")	100 mm x 100 mm x 86.7 mm (3.94" x 3.94" x 3.41")
Sensor Input Aperture	Ø40 mm	Ø25.4 mm	Ø25 mm
Active Detector Area	Ø40 mm	Ø27 mm	Ø25 mm
Distance to Detector^g	13 mm	4.6 mm	15 mm
Cable Length	1.5 m
Connector	D-Sub 9-Pin Male
Weight	1 kg (2.20 lb)	0.71 kg (1.57 lb)	0.75 kg (1.65 lb)
Mounting and Accessories
Post	M6, 75 mm Long Ø1/2" Post Included	Ø1/2" Post via Universal 8-32 & M4 Tap (Post Not Included)	M6, 75 mm Long Ø1/2" Post Included
Cage System Mounting	N/A	N/A	30 mm Cage Systems via Four 4-40 Tapped Holes
Aperture Thread	Unthreaded	Internally SM1-Threaded Aperture with External SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters	Externally SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters
Fiber Adapters (Available Below)	S120 Series Fiber Adapters

For continuous wave (CW) sources, this value is equivalent to the peak power density, while for pulsed laser sources this value is calculated from the time-averaged power and beam profile.
Two Minute Maximum Exposure Time
Measurement taken with the PM100D console, except for the S425C-L in which the PM400 was used. In all cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s) for the S350C and S322C. As the natural response time of the S425C-L is fast, the S425C-L does not benefit from acceleration and this function cannot be enabled. See the Operation tab for additional information.
12 VDC power supply included.
Distance is measured from the detector to the front face of the housing.

High Max Power Density for Pulsed Lasers

Item #	S370C	S470C
Detection Specifications
Detector Type	Thermal Volume Absorber (Axial Thermopile)	Thermal Volume Absorber (Axial Thermopile)
Wavelength Range	0.4 - 5.2 µm	0.25 - 10.6 µm
Optical Power Range	10 mW - 10 W	100 µW - 5 W
Max Power Density	35 W/cm² (Avg); 100 GW/cm² (Peak, 1 ns Pulse)	35 W/cm² (Avg); 100 GW/cm² (Peak, 1 ns Pulse)
Max Pulse Energy Density	1 J/cm² (1 ns pulse) 10 J/cm² (1 ms pulse)	1 J/cm² (1 ns Pulse)
Max Intermittent Power^a	15 W	-
Linearity	±1%	±0.5%
Resolution^b	250 µW	10 µW
Measurement Uncertainty^c (Calibration Uncertainty)	±3% @ 1064 nm ±5% @ 400 - 1064 nm	±3% @ 1064 nm ±5% @ 250 nm - 10.6 µm
Response Time^d	45 s (3 s from 0 to 90%)	6.5 s (<2 s from 0 to 90%)
General Information
Suggested Application	High Peak Power Lasers	High Peak Power, Low Average Power Lasers
Absorber	Broadband Volume Absorber (Schott NG1 Filter)	Broadband Volume Absorber (Schott NG1 Filter)
Cooling	Convection	Convection
Temperature Sensor (In Sensor Head)	N/A	N/A
Console Compatibility	PM400, PM100D, PM100A, PM320E, and PM100USB	PM400, PM100D, PM100A, PM320E, and PM100USB
Mechanical Specs
Housing Dimensions (Without Adapter, if Applicable)	75 mm x 75 mm x 51.2 mm (2.95" x 2.95" x 2.02")	45.0 mm x 45.0 mm x 18.0 mm (1.77" x 1.77" x 0.71")
Input Aperture Size	Ø25 mm	Ø15 mm
Active Detector Area^e	Ø25 mm	>Ø15 mm
Distance to Detector^f	13 mm	5.1 mm
Cable Length	1.5 m	1.5 m
Connector	Sub-D 9-Pin Male	Sub-D 9-Pin Male
Weight	0.5 kg (1.10 lb)	0.1 kg (0.22 lb)
Mounting and Accessories
Post	M6, 75 mm Long Post Included	Universal 8-32 / M4 Tap, Post Not Included
Cage System Mounting	4 x 4-40 Threads for 30 mm Cage Compatibility	N/A
Aperture Thread	Externally SM1-Threaded Adapter for Ø1" Lens Tubes and Fiber Adapters	External SM1-Threaded Aperture for Ø1" Lens Tubes and Fiber Adapters
Fiber Adapters (Available Below)	S120 Series Fiber Adapters	S120 Series Fiber Adapters

Two Minute Maximum Exposure Time
Measurement taken with the PM100D console for the S370C and with the legacy PM200 for the S470C. In all cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <2 s). See the Operation tab for additional information.
Input aperture size is the same as the active sensor area for the S370C. The S470C uses a Schott glass volume absorber that is designed to be slightly larger than the entrance aperture to make it easier to detect a beam that is entering the sensor at an angle.
Distance is measured from the detector to the front face of the housing.

Microscope Slide Thermal Sensor

Item #	S175C
Detection Specifications
Detector Type	Thermal Absorber (Axial Thermopile)
Wavelength Range	0.3 - 10.6 µm
Optical Power Range	100 µW - 2 W
Max Power Density	200 W/cm²
Max Pulse Energy Density	0.1 J/cm² (1 µs pulse) 1 J/cm² (1 ms pulse)
Max Intermittent Power	-
Linearity	±0.5%
Resolution^a	10 µW
Measurement Uncertainty^b (Calibration Uncertainty)	±3% @ 1064 nm ±5% @ 300 nm - 10.6 µm
Response Time^c	3 s (<2 s from 0 to 90%)
General Information
Suggested Application	Light Measurement on the Microscope Objective Plane
Absorber	Broadband Coating
Cooling	Convection
Temperature Sensor (In Sensor Head)	N/A
Console Compatibility	PM400, PM100D, PM100A, PM320E, and PM100USB
Mechanical Specs
Housing Dimensions	76 mm x 25.2 mm x 4.8 mm (2.99" x 0.99" x 0.19")
Input Aperture Size	18 mm x 18 mm
Active Detector Area	18 mm x 18 mm
Distance to Detector^d	1.1 mm
Cable Length	1.5 m
Connector	Sub-D 9-Pin Male
Weight	0.05 kg (0.11 lb)
Mounting and Accessories
Post	N/A
Cage System Mounting	N/A
Aperture Thread	N/A
Fiber Adapters (Available Below)	N/A

Measurement taken with the legacy PM200 console with the acceleration circuit switched off. Resolution performance will be similar with our other power meter consoles.
Measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). See the Operation tab for additional information.
Distance is measured from the detector to the front face of the housing.

C-Series Sensor Connector

D-Type Male

DB9 Male

Pin	Connection
1	Not Used
2	EEPROM Data
3	Sensor and NTC Ground
4	Not Used
5	Not Used
6	EEPROM Ground
7	NTC
8	Sensor Signal
9	Not Used

Operational Principle

Click to Enlarge
Figure 1: A thermal sensor with radially configured thermocouples, which is depicted as seen from the top. Light is incident on the absorbing layer at the center, and heat flows through the thermocouples to the heat sink.

Click to Enlarge
Figure 2: A thermal sensor with axially configured thermocouples, which is depicted as seen from the side. Light is incident on the top, and heat flows down through the thermocouple layer and dissipates in the heat sink below.

Thorlabs' Thermal Power Sensors are based on thermopiles. The top layer of the sensor consists of a light-absorbing material. A region filled with multiple thermocouples, which are connected in series, is immediately adjacent to the absorber. Thermocouples are made by bringing two dissimilar metals into contact, and their point of contact is called a junction. On the other side of the thermocouples is a heat sink. The thermocouples are connected in series, and the placement of the junctions alternates from being in close proximity to the absorber to being in close proximity to the heat sink.

The absorber converts incident light energy into heat. The heat flows from the absorber, across the thermocouples, and to the heat sink, where it dissipates. The temperatures of the thermocouple junctions placed close to the absorber are higher than those the adjacent junctions placed close to the heat sink. This arrangement takes advantage of the thermoelectric (Seebeck) effect, in which a temperature difference between the adjacent junctions generates a proportional voltage difference. By connecting multiple thermocouples in series, the magnitude of the generated voltage is increased. The thermocouples are often arranged in a radial (also called a disk) configuration, as illustrated in Figure 1, or in an axial (also called a matrix) configuration, which is diagrammed in Figure 2. Thermal power sensors with both types of configurations are available from Thorlabs.

Radial Configuration of Thermocouples
A diagram of a thermal power sensor with a radial thermopile is shown in Figure 1, viewed from the top. This construction places the light absorber at the center. It is surrounded by a concentric ring of thermocouples connected in series, which are surrounded by a concentric heat sink. Light incident on the absorber generates heat that flows in a radial direction through the thermocouples and towards the heat sink. The heat sink must be specially designed so that it is in good mechanical contact with the outer ring of thermocouple junctions, without being in thermal contact with the light absorber or the inner ring of thermocouple junctions. The area behind the absorber cannot be in thermal contact with anything that will divert the heat flow from its intended radial path of flow.

A benefit of the radial construction is that sensors can be designed to measure power levels as high as kilowatts. This high upper limit is made possible both by the thickness of the sensor disk and by displacing the thermocouples from the absorber, which protects them from the conditions in the laser impact area. Disadvantages of the radial thermopiles include the use of a heat sink with a special design, which adds complexity when customizing the sensor head, and a sensor head which is generally a least twice the diameter of the active detector area. Resolution for radial thermal power sensors is typically limited to around 10 mW.

Thorlabs' thermal power sensors featuring a radial configuration include the S350C and S322C, which are all designed for mid-power range applications.

Axial Configuration of Thermocouples
A diagram of a thermal power sensor with an axial configuration of thermocouples is shown in Figure 2. In this design, the thermocouples are arranged between two flat layers. One layer is the light absorber, and the other is the heat sink. As the heat flows directly from the front surface to the back side, the dimensions of these sensor packages can be made compact. The sensor housing can be approximately the same size as the active detector area.

The new generation of axially-designed sensors achieves high resolutions in the microwatt range while providing relatively fast response times. These sensors detect optical powers up to several Watts, which limited mostly by the thickness of the absorbing material. The performance of the newly designed sensors, which includes the S401C and S405C, contrasts with sensors of previous generations, which have slower response times.

Heat sink shapes and dimensions are much less constrained for axially, as compared with radially, configured thermopiles. Heat sinks for axial designs can be as simple as a block of aluminum attached with thermal glue, or as sophisticated as a metal-core PCB that is soldered to the sensor. Our S415C, S425C, and S425C-L thermal power sensors have heat sinks can be easily removed and replaced. This enables the user to upgrade the heat sink, potentially to one with fans or water cooling, or to integrate the sensor into a custom setup. Please note that the heat sink must provide heat dissipation adequate for the application.

Volume Absorbers for Pulsed Lasers
Volume absorbers are alternatives to surface absorbers, which sustain damage when subjected to highly energetic and short pulses of nanosecond duration. Unlike surface absorbers, which suffer damage as a consequence of absorbing the pulse energy within a localized region, volume absorbers collect the heat from the light pulse and distribute it throughout a volume. Heat generated throughout the volume flows across the thermocouples and dissipates in the heat sink. Thorlabs offers two thermal power sensors with volume absorbers, S370C and S470C, which are both designed for the detection of Nd:YAG laser pulses, among other applications. In these axially-constructed sensors, the Schott glass volume absorber replaces the surface absorber of the other axial sensors. The response times of sensors with volume absorbers are slower than those with surface absorbers, as the thermal mass of the volume absorber is larger. The S470C is faster than the S370C, as its glass volume is smaller and other design changes have resulted in a faster response of the axial thermopile.

Click to Enlarge
Figure 3: Natural response of the S415C with the dotted line at 99% and the red square indicating the point on the curve corresponding to a single sensor time constant.

Natural Responses, the Sensor Time Constant, and Power Measurement Predictions

The typical natural response of the S415C thermal sensor to an instantaneous transition from darkness to being steadily illuminated is shown in Figure 3. This step function illumination stimulus produces a response that can be modeled using an exponential function and is similar to the function describing the rate at which a capacitor charges.

The sensor time constant is defined in terms of how long it takes for the sensor response to reach 99% of its maximum response. When the sensor has reached the 99% level, a time period equal to five sensor time constants has elapsed. In Figure 3, the dotted line corresponds to the 99% level and the red square to the response after a single sensor time constant has elapsed.

When the sensor's natural response characteristic function is known, it is possible to use it to model and predict the final power reading well before the sensor reading has stabilized. Thorlabs' power meter consoles calculate and display predictions of the stabilized power reading when Thorlabs sensors with sensor time constants ≥0.5 s (natural response times >1 s) are connected. Prediction is implemented using the sensor information stored in the EEPROM built into the C-Series connectors. The S415C, S425C, and S425C-L are fast enough, with sensor time constants <0.2 s (natural response times <0.6 s), that prediction is not necessary and is not enabled. Prediction is enabled for the other sensors.

When prediction is active, the first prediction is made after a time duration equal to a single sensor time constant, and this prediction is updated at time intervals of one sensor time constant until a total time duration of seven sensor time constants has elapsed. Prediction is then turned off; the power reading after seven time constants is 99.9% of the final reading. As there is uncertainty associated with the predicted measurements, they can exhibit some ripple. The faster the sensor, the less the uncertainty. After prediction is turned off, the gradient of the power reading is monitored, and prediction is re-enabled if an increase is detected which exceeds a defined threshold.

Protect Thermal Power Sensors from Thermal Disturbances

For the most accurate results, thermal power sensors should be protected from air flow and other thermal disturbances during operation. Otherwise, measurements will drift. This is of particular importance for low power sensors with high resolution. Handheld use is not recommended for any of the thermal power sensors, as body heat transferred to the sensor or heat sink can negatively impact the accuracy of the measurements.

Thermal power sensors operate by measuring a temperature differential, which is converted to a voltage signal. The sensor design assumes that heat generated in the absorber flows towards the heat sink. If the operator is in contact with the sensor housing during operation, body heat may transfer to the sensor and make spurious contributions to the power measurement. For example, if the sensor is held by the heat sink, heat transferred from the hand to the heat sink will flow towards the absorber. If no light is incident on the absorber, this will result in a negative power reading. If there is light incident on the absorber, it will result in an inaccurate power reading.

Thorlabs offers a wide selection of power and energy meter consoles and interfaces for operating our power and energy sensors. Key specifications of all of our power meter consoles and interfaces are presented below to help you decide which device is best for your application. We also offer self-contained wireless power meters and compact USB power meters.

When used with our C-series sensors, Thorlabs' power meter consoles and interfaces recognize the type of connected sensor and measure the current or voltage as appropriate. Our C-series sensors have responsivity calibration data stored in their connectors. The console will read out the responsivity value for the user-entered wavelength and calculate a power or energy reading.

Photodiode sensors deliver a current that depends on the input optical power and the wavelength. The current is fed into a transimpedance amplifier, which outputs a voltage proportional to the input current. The photodiode's responsivity is wavelength dependent, so the correct wavelength must be entered into the console for an accurate power reading. The console reads out the responsivity for this wavelength from the connected sensor and calculates the optical power from the measured photocurrent.
Thermal sensors deliver a voltage proportional to the input optical power. Based on the measured sensor output voltage and the sensor's responsivity, the console will calculate the incident optical power.
Energy sensors are based on the pyroelectric effect. They deliver a voltage peak proportional to the pulse energy. If an energy sensor is recognized, the console will use a peak voltage detector and the pulse energy will be calculated from the sensor's responsivity.

The consoles and interfaces are also capable of providing a readout of the current or voltage delivered by the sensor. Select models also feature an analog output.

Consoles

Item #	PM100A	PM100D	PM400	PM320E
(Click Photo to Enlarge)
Key Features	Analog Power Measurements	Digital Power and Energy Measurements	Digital Power and Energy Measurements, Touchscreen Control	Dual Channel
Compatible Sensors	Photodiode and Thermal Power	Photodiode and Thermal Power; Pyroelectric
Housing Dimensions (H x W x D)	7.24" x 4.29" x 1.61" (184 mm x 109 mm x 41 mm)	7.09" x 4.13" x 1.50" (180 mm x 105 mm x 38 mm)	5.35" x 3.78" x 1.16" (136.0 mm x 96.0 mm x 29.5 mm)	4.8" x 8.7" x 12.8" (122 mm x 220 mm x 325 mm)
Channels	1			2
External Temperature Sensor Input (Sensor not Included)	-	-	Instantaneous Readout and Record Temperature Over Time	-
External Humidity Sensor Input (Sensor not Included)	-	-	Instantaneous Readout and Record Humidity Over Time	-
GPIO Ports	-		4, Programmable	-
Source Spectral Correction	-	-		-
Attenuation Correction	-	-		-
External Trigger Input	-	-	-
Display
Type	Mechanical Needle and LCD Display with Digital Readout	320 x 240 Pixel Backlit Graphical LCD Display	Protected Capacitive Touchscreen with Color Display	240 x 128 Pixels Graphical LCD Display
Dimensions	Digital: 1.9" x 0.5" (48.2 mm x 13.2 mm) Analog: 3.54" x 1.65" (90.0 mm x 42.0 mm)	3.17" x 2.36" (81.4 mm x 61.0 mm)	3.7" x 2.1" (95 mm x 54 mm)	3.7" x 2.4" (94.0 mm x 61.0 mm)
Refresh Rate	20 Hz		10 Hz (Numerical) 25 Hz (Analog Simulation)	20 Hz
Measurement Views^a
Numerical
Mechanical Analog Needle		-	-	-
Simulated Analog Needle	-
Bar Graph	-
Trend Graph	-
Histogram	-		-
Statistics
Memory
Type	-	SD Card	NAND Flash	-
Size	-	2 GB	4 GB	-
Power
Battery	LiPo 3.7 V 1300 mAh		LiPo 3.7 V 2600 mAh	-
External	5 VDC via USB or Included AC Adapter		5 VDC via USB	Selectable Line Voltage: 100 V, 115 V, 230 V (±10%)

These are the measurement views built into the unit. All of our power meter consoles except the PM320E can be controlled using the Optical Power Monitor software package. The PM320E has its own software package.

Interfaces

Item #	PM101	PM101A	PM101R	PM101U	PM100USB
(Click Photo to Enlarge)
Key Features	USB, RS232, UART, and Analog Operation	USB and Analog SMA Operation	USB and RS232 Operation	USB Operation	USB Operation
Compatible Sensors	PM101 Series: Photodiode and Thermal Power PM102 Series: Thermal Power and Thermal Position & Power				Photodiode and Thermal Power; Pyroelectric
Housing Dimensions (H x W x D)	3.80" x 2.25" x 1.00" (96.5 x 57.2 x 25.4 mm)	3.94" x 2.25" x 1.00" (100.0 x 57.2 x 25.4 mm)	3.78" x 2.25" x 1.00" (95.9 x 57.2 x 25.4 mm)	3.68" x 2.25" x 1.00" (93.6 x 57.2 x 25.4 mm)	3.67" x 2.38 " x 1.13" (93.1 x 60.4 x 28.7 mm)
Channels	1
External Temperature Sensor Input (Sensor Not Included)	NTC Thermistor	-
External Humidity Sensor Input (Sensor not Included)	-
GPIO Ports	-
Source Spectral Correction	-
Attenuation Correction	-
External Trigger Input	-
Display
Type	No Built-In Display; Controlled via GUI for PC
Refresh Rate	Up to 1000 Hz^a				Up to 300 Hz^a
Measurement Views^b
Numerical	Requires PC^b
Mechanical Analog Needle	-
Simulated Analog Needle	Requires PC^b
Bar Graph	Requires PC^b
Trend Graph	Requires PC^b
Histogram	Requires PC^b
Statistics	Requires PC^b
Memory
Type	Internal Non-Volatile Memory for All Settings				-
Size	-
Power
Battery	-
External	5 VDC via USB or 5 to 36 VDC via DA-15	5 VDC via USB

Dependent on PC Settings
These power meter interfaces do not have a built-in monitor, so all data must be displayed through a PC running the Optical Power Meter Software.

Pulsed Laser Emission: Power and Energy Calculations

Click above to download the full report.

Determining whether emission from a pulsed laser is compatible with a device or application can require referencing parameters that are not supplied by the laser's manufacturer. When this is the case, the necessary parameters can typically be calculated from the available information. Calculating peak pulse power, average power, pulse energy, and related parameters can be necessary to achieve desired outcomes including:

Protecting biological samples from harm.
Measuring the pulsed laser emission without damaging photodetectors and other sensors.
Exciting fluorescence and non-linear effects in materials.

Pulsed laser radiation parameters are illustrated in Figure 1 and described in the table. For quick reference, a list of equations are provided below. The document available for download provides this information, as well as an introduction to pulsed laser emission, an overview of relationships among the different parameters, and guidance for applying the calculations.

Equations:
Period and repetition rate are reciprocal:		and
Pulse energy calculated from average power:
Average power calculated from pulse energy:
Peak pulse power estimated from pulse energy:
Peak power and average power calculated from each other:
	and
Peak power calculated from average power and duty cycle*:
	*Duty cycle () is the fraction of time during which there is laser pulse emission.

Click to Enlarge

Figure 1: Parameters used to describe pulsed laser emission are indicated in the plot (above) and described in the table (below). Pulse energy (E) is the shaded area under the pulse curve. Pulse energy is, equivalently, the area of the diagonally hashed region.

Parameter	Symbol	Units
Pulse Energy	E	Joules [J]	A measure of one pulse's total emission, which is the only light emitted by the laser over the entire period. The pulse energy equals the shaded area, which is equivalent to the area covered by diagonal hash marks.
Period	Δt	Seconds [s]	The amount of time between the start of one pulse and the start of the next.
Average Power	P_avg	Watts [W]	The height on the optical power axis, if the energy emitted by the pulse were uniformly spread over the entire period.
Instantaneous Power	P	Watts [W]	The optical power at a single, specific point in time.
Peak Power	P_peak	Watts [W]	The maximum instantaneous optical power output by the laser.
Pulse Width		Seconds [s]	A measure of the time between the beginning and end of the pulse, typically based on the full width half maximum (FWHM) of the pulse shape. Also called pulse duration.
Repetition Rate	f_rep	Hertz [Hz]	The frequency with which pulses are emitted. Equal to the reciprocal of the period.

Example Calculation:

Is it safe to use a detector with a specified maximum peak optical input power of 75 mW to measure the following pulsed laser emission?

Average Power: 1 mW
Repetition Rate: 85 MHz
Pulse Width: 10 fs

The energy per pulse:

seems low, but the peak pulse power is:

It is not safe to use the detector to measure this pulsed laser emission, since the peak power of the pulses is >5 orders of magnitude higher than the detector's maximum peak optical input power.

Click to Enlarge
The PM160 wireless power meter, shown here with an iPad mini (not included), can be remotely operated using Apple mobile devices.

This tab outlines the full selection of Thorlabs' power and energy sensors. Refer to the lower right table for power meter console and interface compatibility information.

In addition to the power and energy sensors listed below, Thorlabs also offers all-in-one, wireless, handheld power meters and compact USB power meter interfaces that contain either a photodiode or a thermal sensor, as well as power meter bundles that include a console, sensor head, and post mounting accessories.

Thorlabs offers four types of sensors:

Photodiode Sensors: These sensors are designed for power measurements of monochromatic or near-monochromatic sources, as they have a wavelength dependent responsivity. These sensors deliver a current that depends on the input optical power and the wavelength. The current is fed into a transimpedance amplifier, which outputs a voltage proportional to the input current.
Thermal Sensors: Constructed from material with a relatively flat response function across a wide range of wavelengths, these thermopile sensors are suitable for power measurements of broadband sources such as LEDs and SLDs. Thermal sensors deliver a voltage proportional to the input optical power.
Thermal Position & Power Sensors: These sensors incorporate four thermopiles arranged as quadrants of a square. By comparing the voltage output from each quadrant, the unit calculates the beam's position.
Pyroelectric Energy Sensors: Our pyroelectric sensors produce an output voltage through the pyroelectric effect and are suitable for measuring pulsed sources, with a repetition rate limited by the time constant of the detector. These sensors will output a peak voltage proportional to the incident pulse energy.

Console Compatibility
Console Item #	PM100A	PM100D	PM400	PM320E	PM101 Series	PM102 Series	PM100USB
Photodiode Power						-
Thermal Power
Thermal Position	-	-		-	-		-
Pyroelectric Energy	-				-	-

Power and Energy Sensor Selection Guide

There are two options for comparing the specifications of our Power and Energy Sensors. The expandable table below sorts our sensors by type (e.g., photodiode, thermal, or pyroelectric) and provides key specifications.

Alternatively, the selection guide graphic further below arranges our entire selection of photodiode and thermal power sensors by wavelength (left) or optical power range (right). Each box contains the item # and specified range of the sensor. These graphs allow for easy identification of the sensor heads available for a specific wavelength or power range.

Photodiode Power Sensors

Thermal Power Sensors

Thermal Position & Power Sensors

Pyroelectric Energy Sensors

The response time of the photodiode sensor. The actual response time of a power meter using these sensors will be limited by the update rate of your power meter console.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s) when the natual response time is approximately 1 s or greater. As the natural response times of the S415C, S425C, and S425C-L are fast, these do not benefit from accelerated measurements and this function cannot be enabled. For more information, see the Operation tab here.
With intermittent use: maximum exposure time of 20 minutes for the S401C, otherwise maximum exposure time is 2 minutes.
All pyroelectric sensors have a 20 ms thermal time constant, τ. This value indicates how long it takes the sensor to recover from a single pulse. To detect the correct energy levels, pulses must be shorter than 0.1τ and the repetition rate of your source must be well below 1/τ.

Sensor Options
(Arranged by Wavelength Range)

Sensor Options
(Arranged by Power Range)

Sensor Key

Posted Comments:

Ronald Sipkema (posted 2020-07-14 09:06:51.93)

L.S., I'm interested in using the S425C in combination with either a PM101 or PM100USB for OEM use / integration into a machine. Is it possible to order the sensor with a different cable length or alternatively shorten or lengthen the fixed cable attached to the sensor head ourselves? What would be practical limits on the cable length from sensor to meter? Similarly the PM16-425 might also be an interesting solution, except for the fixed cable length and the fact that the combined electronics / USB plug probably won't fit through a cable carrier or cable hose. Are there options for changing cable length on those sensors?

dpossin (posted 2020-07-16 08:23:45.0)

Dear Ronald, Thank you for your feedback. We did not test at what length the data transfer does not work any more but up to 3m works for sure. We can either offer special power heads with longer cables or you lengthen the cable yourself. The cable of the USB powermeter PM16-425 can be easily extended by a USB to USB extension cable.

Alp Ucak (posted 2020-06-26 12:09:54.14)

Hello, at our laboratory, we are using S350C to measure power. Our beam diameter is about 3mm fwhm and the average power is 25W with 350fs laser pulses. At our measurements, we observe an initial rise and we suspect of the powermeter heating problems. It is getting about 45 celsius degrees. Does that create a problem? Should we use a fan or is there another solution?

dpossin (posted 2020-07-02 10:02:19.0)

Dear Alp, Thank you for your feedback. Most probably the average power of your laser is too high which leads to the fact that the heat sink is not able to dissipate all the heat. I am reaching out to you in order to provide further help.

Joseph Donovan (posted 2019-09-18 08:11:55.98)

Hi, I was wondering if the surface of the S425C-L can tolerate short pulsed sources well (the S370C doesn't have enough power handling for our needs). The laser we're using is 1035 nm, max. power 60W (though will be mostly used around 20W), ~300fs pulses at 1MHz, ~3mm beam diameter.

dpossin (posted 2019-09-20 02:49:18.0)

Dear Joseph, Thank you for your feedback. We do not tested this but we have at least one customer who uses our high power thermal sensors in the fs regime at a pulse peak power of 0.1 MW. At the repetition rate you would like to use the laser, the operating mode can be seen as quasi CW (continues wave). In case you want to use the laser at a average power of 20W you will get a pulse peak power of about 67 MW. At 20W, the heat dissipation should be no problem but I am a bit concerned if the absorption layer on the detector surface can survive the high peak power.

Andrey Kuznetsov (posted 2019-04-11 21:31:28.367)

What are the noise figures for all the products in units of Watts? This would help to choose a meter based on how sensitive the measurement can be while not being overpowered by the noise.

nreusch (posted 2019-04-18 05:04:50.0)

This is a response from Nicola at Thorlabs. Thank you for your suggestion! The optical power range specification in combination with the resolution (both specified in Watts) should allow you to determine whether your optical signal can be detected. These features contain all limiting factors including noise.

gizem.alpakut (posted 2019-01-22 08:00:48.627)

Hi, I have a question regarding S425C-L and S121C pwoermeter sensors. Whenever I measure a specific power value using both of them, I always get different results. S425C-L always gives 50% less power value than S121C does. I am well aware that S425C-L is a thermal power sensor and other is a photodiode, I used PM100D and PM100USB as power meter consoles, which automatically recognize the console type. What can be the resson for that difference? Is there a way to fix this problem? Thanks in advance.

nreusch (posted 2019-01-23 10:50:02.0)

This is a response from Nicola at Thorlabs. Thank you very much for your inquiry. You are right about the fact that such differences are mostly due to the different nature of both sensors. This is especially the case for e.g. broadband sources, for larger angles of incidence (relevant for the photodiode sensor) or for pulsed sources. I will get back to you directly to discuss your specific application.

spanna (posted 2018-12-30 14:08:20.63)

Dear Thorlabs, I have two questions regarding the S425C-L model: 1. Below what power I can safely remove the heatsink, my laser provides 6mJ (6W @ 1kHz rep.rate) 35fs pulses with 11mm full width 1/e2 spot size? 2. Does the heatsink removal affect the detector calibration or its reading in any way? Thanks in advance

swick (posted 2019-01-08 04:00:56.0)

This is a response from Sebastian at Thorlabs. Thank you for the inquiry. 1. When measuring low optical powers we recommend for stability reasons to use thermal detectors with heat-sinks. Removing the heat sink provides the option to use other type of heat-sinks like water-cooling. 2. Calibration should not be affected if heat-sink is replaced with an other appropriate one. I contacted you directly for further discussion.

cwong3 (posted 2017-01-16 18:00:18.07)

Hi there. Can you tell me what the max energy density would be for a 30 fs pulse? I'm mostly interested in the S470C and S310C. Thanks.

wskopalik (posted 2017-01-17 05:13:38.0)

This is a response from Wolfgang at Thorlabs. Thank you very much for your inquiry. Unfortunately, we don't have specifications for the maximum energy density for fs pulses. Depending on the exact laser parameters (wavelength, pulse energy, repetition rate, etc.) one of our sensors might however still be suitable. I have contacted you directly to further discuss your requirements and to look for a suitable sensor.

arkke.eskola (posted 2016-10-27 12:06:48.73)

Hi, I am searching a (thermal) sensor, which would work both with excimer laser (193, 248, and 351 nm) and Nd:YAG laser (213, 266, 355, and 532 nm). I am thinking your S350C sensor due to its large aperture size and wide wavelenght range. Could you please comment its suitability for this purpose; especially I would like to know whether there might appear any issue(s) to use S305C to measure (short) Nd:YAG laser pulse energies. Or should I think about pyroelectric energy sensors? Thanks, Arkke Eskola

wskopalik (posted 2016-10-28 05:19:58.0)

This is a response from Wolfgang at Thorlabs. Thank you for your inquiry. Thermal sensors are generally a good choice to measure the average power of pulsed lasers. It depends on the exact laser parameters which sensor model is the most suited (i.e. wavelength, pulse energy, pulse width, repetition rate, beam diameter). These parameters are necessary to make sure that the sensor can handle the power levels of the laser and will not be damaged by it. I will contact you directly to further discuss your requirements.

kedves (posted 2016-04-13 18:29:51.247)

Hello, I am looking for a power meter for a femtosecond laser of about 25 mJ pulse energy, 10 Hz repetition rate (i.e. 250 mW average power), and 40 fs pulse duration (i.e. 625 GW pulse peak power) and 15 mm pulse diameter. Which of your products would you recommend that can tolerate this high peak power too?

shallwig (posted 2016-04-14 10:34:42.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry. At the moment we have no sensor available which is specified to stand 625 GW peak power and 353,7 GW/cm2 peak power density. I will contact you directly to discuss if there is a special solution we can offer.

mastron (posted 2016-02-24 19:42:46.833)

I am looking into power meters and sensors for measurements of ultrafast pulsed lasers (pulses <250fs at 1khz). Would the S470C be appropriate for this kind of measurement? I wouldn't need shot-to-shot resolution; just to be able to measure pulse energies in several ranges: low uJ (so at 1 khz, low mW range), ~500mW, and ~2W without damaging the power sensor. Also, are calibration options available for multiple wavelength regions? I'd like to be able to measure visible, 800 nm, and near to mid-IR (so around 1.5, 2, 5, and 6 um) accurately.

shallwig (posted 2016-02-25 10:16:16.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry due to its long response time (<2s) as typical for thermal sensors average power measurements of pulsed sources are possible. The calibration and measurement uncertainty of this sensor are specified from 250nm – 10,6µm. More information about the calibration of our thermal heads can be found in the power meter tutorial in the “calibration “ Tab here: http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6188 I will contact you directly to discuss your application and your parameters in more detail.

user (posted 2015-12-16 15:42:00.627)

In addition to my question below, would you please advice me if you conducted calibration with any emmersion oil? How would it be calibrated with angled beam?

shallwig (posted 2015-12-16 05:09:11.0)

This is a response from Stefan from Thorlabs. Thank you again for your for your inquiry. We calibrate the sensor S175C at 1064nm with a collimated laser at 100mW, the beam hits the sensors surface perpendicular. Apart from the calibration at 1064nm we do perform a reflectivity measurement were the reflectivity of the coating gets measured from 266 – 1064nm . In our power meter tutorial the whole process gets described in detail: http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6188 We have a NIST traceable reference built in a integrating sphere and measure the spectral intensity distribution. Afterwards we put the sensor under test in and measure the spectral reflectivity again. The difference between both curves tells us about the reflectivity of the sensors absorber surface. This is the calibration curve you also get delivered with the sensor. But there is no NIST standard available which allows to calibrate the sensors with angled beams so far. Therefore we cannot specify any measurement accuracy for this measurement task.

user (posted 2015-12-16 13:57:56.547)

I am interested in you S175C sensor to measure oure Ti:Sa laser under 20X objective(oil emmersion). We can't know about real power under the objective as we have not had any sensor. But guessing it would be 500mW-less than 1W. Can we use your S175C for our measurment?

shallwig (posted 2015-12-16 04:37:05.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry. For estimation how suitable this sensor is for power measurement of your Ti:Sa I would need further information about the beam. We specify for the sensor a maximum average power density of 200W/cm2 and for µs Pulses and a max pulse energy density of 0.1J/cm2 and 1J/cm2 for 1ms pulses. You can find these information in the spec sheet: http://www.thorlabs.de/thorcat/MTN/S175C-SpecSheet.pdf The measurement accuracy we specify is only valid for parallel beams with diameter >1mm. I would like to discuss your application in more detail with you directly, unfortunately you left no email address. Please feel free to contact me at europe@thorlabs.com

hsynvnvural (posted 2015-11-20 09:55:12.33)

Is there any difference between CW/Pulsed Laser average power measurement for thermopile sensors? Is the uncertainty same for both measurement for S350C and S470C sensors?

shallwig (posted 2015-11-20 10:09:03.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry. In general Thermopile sensors have a very slow response time, for the S470C we specify <2s. Depending on the repetition rate of your pulsed source multiple of pulses will hit the active surface before a measurement point is taken. The measurement uncertainty for the S350C and S470C can be found in the specs table: ±3% @ 351 nm; ±5% @ 190 - 1100 nm (S350C) and ±3% @ 1064 nm; ±5% @ 250 nm - 10.6 µm (S470C) A main difference apart from the power range is the detector type. The S350C is a thermal surface absorber while the S470C is a thermal volume absorber. Thermal volume absorbers have significantly higher responsivities, which allow them to detect very low power levels and short (ns) pulses. However, this improvement usually comes at the expense of response time. I will contact you directly to check which sensor is suited for your application.

Paul.taylor (posted 2015-03-20 11:12:45.53)

Can you read the voltage direct from the head via a Plc analog input card? If so - what rough calibration V/W is it?

shallwig (posted 2015-03-23 06:13:37.0)

This is a response from Stefan at Thorlabs. Thank you very much for your inquiry. You can use a PLC analog input card to read out the voltage directly by taking the generated thermo voltage from Pin 3 and 8 of the D-Sub connector. Please take a look into the “Pin Diagrams” Tab on the website http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3333 With the sensor head you will get a calibration certificate where the sensitivity at our calibration sources (1062nm) is listed with an uncertainty of +/-3%. Depending on which sensor you are interested in the sensitivity is between 0,1mV/W and about 100mV/W. Thus you have to deal with very small voltages. Further information about how our thermal sensors get calibrated can be also found in the power meter tutorial on our website: http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6188 in the “calibration” tab. I will contact you directly to discuss your application in more detail.

tonyhongxp (posted 2015-02-10 22:20:54.77)

would the thermal power meter work below 190 nm? The absorption curve does not seem to fall at wavelength below 190 nm.

tschalk (posted 2015-02-11 08:03:01.0)

This is a response from Thomas at Thorlabs. Thank you very much for your inquiry. You can use the sensor below 190nm but we dont have specific informaiton about the sensitivity and we dont have the possibility to calibrate the sensor below that wavelength. I will contact you directly to discuss your application.

user (posted 2011-11-28 09:07:26.0)

A response from Tyler at Thorlabs: Hello Krister, The thermal power meter sensors that Thorlabs sells use a thermopile sensor to measure the incident power. These sensors would not be an out-of-the-box solution for a non-contact temperature sensor. We will contact you to discuss your application and possible solutions.

krister.magnusson (posted 2011-11-28 05:57:45.0)

This product measures light intensity. Does it also include a laser which send out a detection signal wich is analyzed? That is, how does it operate? I am looking for a non-contact temperature sensor (not pyrometer). Best regards, Krister Magnusson

jjurado (posted 2011-07-08 15:18:00.0)

Javier Jurado: Response from Javier at Thorlabs to last poster: We do offer a cap that you can use to cover the entrance port of the S302C sensor. The part number is SM1CP1: http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3519 Please do not hesitate to contact us at techsupport@thorlabs,com if you have any further questions.

user (posted 2011-07-08 15:50:53.0)

I ordered S302C and I would like protect its window. Do you sell a cap for it?

jjurado (posted 2011-06-02 11:34:00.0)

Response from Javier at Thorlabs to halverso: Thank you very much for contacting us. With a maximum incident power density spec of 200W/cm^2, the S302C should work for your application. However, other parameters such as wavelength range, minimum incident power, and beam diameter are important, as well, in order to determine the most suitable sensor. I will contact you directly to discuss these details.

halverso (posted 2011-06-02 09:18:06.0)

I want to measure power on a stable solar simulator. Expected value is 100mW/cm2. The S302C appears to be ideal for my purpose, but I wanted to confirm. Thanks.

apalmentieri (posted 2010-02-22 22:55:57.0)

A response from Adam at Thorlabs to malayk: The S302C sensors are not compatible with the old PM100 power meters. They are compatible with the new PM100D power meter. I will contact you directly to help provide you with the best possible solution that suits your needs.

malayk (posted 2010-02-22 22:00:52.0)

Is the S302C sensor compatible with the old PM100 power meter?

High Resolution

Item #^a	S401C	S405C
Sensor Image (Click the Image to Enlarge)
Wavelength Range	190 nm - 20 µm	190 nm - 20 µm
Optical Power Range	10 µW - 1 W (3 W^b)	100 µW - 5 W
Input Aperture Size	Ø10 mm	Ø10 mm
Active Detector Area	10 mm x 10 mm	10 mm x 10 mm
Max Optical Power Density	500 W/cm² (Avg.)	1.5 kW/cm² (Avg.)
Detector Type	Thermal Surface Absorber (Thermopile) with Background Compensation	Thermal Surface Absorber (Thermopile)
Linearity	±0.5%	±0.5%
Resolution^c	1 µW	5 µW
Measurement Uncertainty^d	±3% @ 1064 nm ±5% @ 190 nm - 10.6 µm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm
Response Time^e	1.1 s	1.1 s
Cooling	Convection (Passive)
Housing Dimensions (Without Adapter)	33.0 m x 43.0 mm x 15.0 mm (1.30" x 1.69" x 0.59")	40.6 mm x 40.6 mm x 16.0 mm (1.60" x 1.60" x 0.63")
Temperature Sensor (In Sensor Head)	NTC Thermistor	NTC Thermistor
Cable Length	1.5 m
Post Mounting	Universal 8-32 / M4 Taps (Post Not Included)	Universal 8-32 / M4 Taps (Post Not Included)
30 mm Cage Mounting	-	Two 4-40 Tapped Holes & Two Ø6 mm Through Holes
Aperture Threads	-	Internal SM05
Accessories	Externally SM1-Threaded Adapter Light Shield with Internal SM05 Threading	Externally SM1-Threaded Adapter
Compatible Consoles	PM400, PM100D, PM100A, PM100USB, PM101A, and PM320E

For complete specifications, please see the Specs tab.
For conditions of intermittent use, with a maximum exposure time of 20 minutes for the S401C. The S405C saturates for optical input powers >5 W.
Measurement taken with the legacy PM200 console for the S401C and the PM400 console for the S405C. In all cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Defined as the measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). See the Operation tab for additional information.

High Resolution of 1 μW or 5 μW
S401C and S405C Have Thermistors Used to Monitor Temperature of Sensor Head
S401C: Background Compensation for Low-Drift Measurements
S405C: Accommodates Average Optical Power Densities up to 1.5 kW/cm²

Click to Enlarge
S401C Thermal Sensor with Included Light Shield

Thorlabs offers two broadband thermal power sensors designed to measure low optical power sources with high resolution. Both thermal sensor's broadband coating has a flat spectral response over a wide wavelength range, as shown in the plot below. The aperture size of Ø10 mm allows for easy alignment and measurement of large-spot-size laser sources. For easy integration with Thorlabs' lens tube systems and SM1-threaded (1.035"-40) fiber adapters (available below), both sensors include an externally SM1-threaded adapter.

The S401C uses active thermal background compensation to provide low-drift power measurements. This is implemented through the use of two sensor circuits to measure heat flow between the light absorber and heat sink in both directions. The measurements of the two sensor circuits are then subtracted, which minimizes the effect of thermal drift on the laser power measurement. (For information about how external thermal disturbances can affect thermal power sensor readings, please see the Operation tab.) The S401C's broadband coating offers high absorption at wavelengths between 0.19 and 20 µm (shown in the graph below), which makes it ideal for use with aligning and measuring Mid-IR Quantum Cascade Lasers (QCLs). The included, internally SM05-threaded (0.535"-40) light shield is shown in the photo above.

The S405C has internal SM05 (0.535"-40) threading that is directly compatible with our SM05 lens tubes, and it can also connect directly to Thorlabs' 30 mm Cage Systems.

Thorlabs offers a recalibration service for these sensors, which can be ordered below (see Item # CAL-S200).

Low Power High Resolution Thermal Sensor Absorption

Click to Enlarge
Raw Data: S401C, S405C
The S405 shares the same absorption curve with the S415C, S425C, and S245C-L. (All are sold below.)

Max Power: 10 W

Item #^a	S415C	S425C
Sensor Image (Click Image to Enlarge)
Wavelength Range	190 nm - 20 µm	190 nm - 20 µm
Optical Power Range	2 mW - 10 W (20 W^b)	2 mW - 10 W (20 W^b)
Input Aperture Size	Ø15 mm	Ø25.4 mm
Active Detector Area	Ø15 mm	Ø27 mm
Max Optical Power Density	1.5 kW/cm² (Avg.)	1.5 kW/cm² (Avg.)
Detector Type	Thermal Surface Absorber (Thermopile)
Linearity	±0.5%	±0.5%
Resolution^c	100 µW	100 µW
Measurement Uncertainty^d	±3% @ 1064 nm ±5% @ 250 nm - 17 µm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm
Response Time^e	0.6 s	0.6 s
Cooling	Convection (Passive)
Housing Dimensions (Without Adapter)	50.8 mm x 50.8 mm x 35.0 mm (2.00" x 2.00" x 1.38")	50.8 mm x 50.8 mm x 35.0 mm (2.00" x 2.00" x 1.38")
Temperature Sensor (In Sensor Head)	NTC Thermistor
Cable Length	1.5 m
Post Mounting	Universal 8-32 / M4 Taps (Post Not Included)	Universal 8-32 / M4 Taps (Post Not Included)
30 mm Cage Mounting	-	-
Aperture Threads	Internal SM1	Internal SM1
Removable Heatsink	Yes	Yes
Accessories	Externally SM1-Threaded Adapter	Externally SM1-Threaded Adapter
Compatible Consoles	PM400, PM100D, PM100USB, PM100A, PM101A, and PM320E

For complete specifications, please see the Specs tab.
Two Minute Maximum Exposure Time
Measurement taken with the PM400 with the acceleration circuit switched off. Resolution performance will be similar with our other power meter consoles.
Defined as the measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). As the natural response times of the S415C and S425C are fast, these do not benefit from accelerated measurements and this function cannot be enabled. See the Operation tab for additional information.

100 µW Optical Power Resolution
Thermistors Used to Monitor Temperature of Sensor Head
Removable Heat Sinks Included

These thermal power sensors are designed for general broadband power measurements of low and medium power light sources. All include an externally SM1-threaded (1.035"-40) adapter, with threading concentric with the input aperture. The adapters are useful for mounting Ø1" Lens Tubes and Fiber Adapters (available below). The apertures of the S415C and S425C have internal SM1 threading.

These sensors operate with fast (<0.6 s) natural response times, and their removable heat sinks provide a high degree of flexibility to those interested in integrating them into custom setups or replacing the included heat sink with one that is water or fan cooled. If replacing the heat sink, please note that the replacement must provide heat dissipation adequate for the application.

Thorlabs offers a recalibration service for these sensors, which can be ordered below (see Item # CAL-S200).

Thermal Sensor Absorption Mid-Power Thermal

Click to Enlarge
Click Here for Raw Data
The absorption curves of each of the thermal power sensors designed for use with low and medium power optical sources.

Max Power: 40 W to 200 W

Click to Enlarge
Raw Data: S350C, S425C-L, S322C
The absorption curves of each of the thermal power sensors designed for use with low and medium power optical sources.

Thermistors Used to Monitor Temperature of Sensor Head
S322C Has 4-40 Taps for Use with Our 30 mm Cage Systems
S350C Has Ø40 mm Aperture Well Suited to Excimer and Other Lasers with Large Spot Sizes
S425C-L Features Removable Heat Sink
S322C is Fan Cooled with an Optical Power Range up to 200 W

These thermal power sensors are designed for general broadband power measurements of low and medium power light sources. With the exception of the S350C, all include an adapter with external SM1 (1.035"-40) threading concentric with the input aperture. This allows the sensors to be integrated into existing Ø1" lens tube systems in addition to being compatible with fiber adapters (available below). The aperture of the S425C-L has internal SM1 threading.

The S425C-L operates with a fast (<0.6 s) natural response time and has a removable heat sink, which provides a high degree of flexibility to those interested in integrating them into custom setups or replacing the included heat sink with one that is water or fan cooled. If replacing the heat sink, please note that the replacement must provide heat dissipation adequate for the application.

Thorlabs offers a recalibration service for these sensors, which can be ordered below (see Item # CAL-S200).

Item #^a	S350C	S425C-L	S322C
Sensor Image (Click Image to Enlarge)
Wavelength Range	190 nm- 1.1 µm, 10.6 µm	190 nm - 20 µm	250 nm - 11 µm
Optical Power Range	10 mW - 40 W (60 W^b)	2 mW - 50 W (75 W^b)	100 mW - 200 W (250 W^b)
Input Aperture Size	Ø40 mm	Ø25.4 mm	Ø25 mm
Active Detector Area	Ø40 mm	Ø27 mm	Ø25 mm
Max Optical Power Density	2 kW/cm² (Avg.)	1.5 kW/cm² (Avg.)	4 kW/cm² (Avg., CO₂)
Detector Type	Thermal Surface Absorber (Thermopile)
Linearity	±1%	±0.5%	±1%
Resolution^c	1 mW	100 µW	5 mW
Measurement Uncertainty^d	±3% @ 351 nm ±5% @ 190 nm - 1100 nm	±3% @ 1064 nm ±5% @ 250 nm - 17 µm	±3% @ 1064 nm ±5% @ 266 nm - 1064 nm
Response Time^e	9 s (1 s from 0 to 90%)	0.6 s	5 s (1 s from 0 to 90%)
Cooling	Convection (Passive)		Forced Air with Fan^f
Housing Dimensions (Without Adapter, if Applicable)	100 mm x 100 mm x 54.2 mm (3.94" x 3.94" x 2.13")	100.0 mm x 100.0 mm x 58.0 mm (3.94" x 3.94" x 2.28")	100 mm x 100 mm x 86.7 mm (3.94" x 3.94" x 3.41")
Temperature Sensor (In Sensor Head)	NTC Thermistor
Cable Length	1.5 m
Post Mounting	M6 Threaded Taps, Includes Ø1/2" Post, 75 mm Long	Universal 8-32 / M4 Taps (Post Not Included)	M6 Threaded Taps, Includes Ø1/2" Post, 75 mm Long
30 mm Cage Mounting	-	-	Four 4-40 Tapped Holes
Aperture Threads	-	Internal SM1	-
Removable Heatsink	-	Yes	-
Accessories	-	Externally SM1-Threaded Adapter	Externally SM1-Threaded Adapter
Compatible Consoles	PM400, PM100D, PM100USB, PM100A, PM101A, and PM320E

For complete specifications, please see the Specs tab.
Two Minute Maximum Exposure Time
Measurement taken with the PM100D console, except for the S425C-L in which the PM400 was used. In all cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Defined as the measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s) for the S350C and S322C. As the natural response time of the S425C-L is fast, the S425C-L does not benefit from acceleration and this function cannot be enabled. See the Operation tab for additional information.
12 VDC power supply is included.

High Max Power Density for Pulsed Lasers

Item #^a	S370C	S470C
Sensor Image (Click Image to Enlarge)
Wavelength Range	400 nm - 5.2 µm	250 nm - 10.6 µm
Optical Power Range	10 mW - 10 W (15 W^b)	100 µW - 5 W (Pulsed and CW)
Input Aperture Size	Ø25 mm	Ø15 mm
Active Detector Area	Ø25 mm	Ø16 mm
Max Optical Power Density	35 W/cm² (Avg.); 100 GW/cm² (Peak)
Detector Type	Thermal Volume Absorber (Thermopile)
Linearity	±1%	±0.5%
Resolution^c	250 µW	10 µW
Measurement Uncertainty^d	±3% @ 1064 nm ±5% @ 400 nm - 1064 nm	±3% @ 1064 nm ±5% @ 250 nm - 10.6 µm
Response Time^e	45 s (3 s from 0 to 90%)	6.5 s (<2 s from 0 to 90%)
Cooling	Convection (Passive)
Housing Dimensions (Without Adapter, if Applicable)	75 mm x 75 mm x 51.2 mm (2.95" x 2.95" x 2.02")	45.0 mm x 45.0 mm x 18.0 mm (1.77" x 1.77" x 0.71")
Temperature Sensor (In Sensor Head)	N/A	N/A
Cable Length	1.5 m
Post Mounting	M6 Threaded Taps, Includes Ø1/2" Post, 75 mm Long	Universal 8-32 / M4 Tap (Post Not Included)
30 mm Cage Mounting	Four 4-40 Tapped Holes	-
Aperture Threads	-	External SM1
Accessories	Externally SM1-Threaded Adapter	-
Compatible Consoles	PM400, PM100D, PM100USB, PM100A, PM101A, and PM320E

For complete specifications, please see the Specs tab.
Two Minute Maximum Exposure Time
Measurement taken with the PM100D console for the S370C and with the legacy PM200 for the S470C. In all cases, the acceleration circuit was switched off. Resolution performance will be similar with our other power meter consoles.
Defined as the measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <2 s). See the Operation tab for additional information.

Designed for Optical Power Measurements of Nd:YAG Lasers
Ideal for Applications with High Peak Pulse Powers
S370C: Ø25 mm Aperture for Large-Spot-Size Beams
S470C: High-Sensitivity for High-Peak-Power Pulses with Low Average Power

The S370C and S470C Thermal Sensors are designed to measure short and highly energetic laser pulses. All of these units are post-mountable for free-space applications and feature NIST-traceable data stored in the sensor connector.

These thermal power sensors are unique in that they have thermal volume absorbers, where our other thermal power sensors have thermal surface absorbers. The volume absorber consists of a Schott glass filter. Incident pulses are absorbed and the heat is distributed throughout the volume. In this way, pulses that would have damaged the absorption coating of a thermal surface absorber are safely measured by these thermal volume absorbers.

The S370C features a large Ø25 mm aperture ideal for large-spot-size beams, and it is compatible with average powers from 10 mW to 10 W (CW).

In comparison, the S470C is faster, as the glass absorber volume is reduced and other design parameters have been optimized for speed. This results in a different optical power range, with the ability to measure powers down to 100 µW. The Ø15 mm aperture is of the S470C is smaller, and it has a lower max average power of 5 W. Its 10 µW resolution is better than the 250 µW resolution of the S370C.

For high-power, pulsed-lasers the S370C and S470C Thermal Sensors can withstand high average and peak power densities. However, for sensors with a broader spectral range or shorter response time, consider one of our Pyroelectric Energy Sensors.

Thorlabs offers a recalibration service for these sensors, which can be ordered below (see Item # CAL-S200).

Click to Enlarge
Click Here for Raw Data
This absorption curve is shown over a broader wavelength range than the sensors' operating ranges. See the table for the operating wavelength range of each sensor.

Microscope Slide Thermal Sensor

Item #^a	S175C
Sensor Image (Click Image to Enlarge)
Wavelength Range	0.3 - 10.6 µm
Power Range	100 µW - 2 W
Input Aperture Size	18 mm x 18 mm
Active Detector Area	18 mm x 18 mm
Max Optical Power Density	200 W/cm²
Detector Type	Thermal Surface Absorber (Thermopile)
Linearity	±0.5%
Resolution^b	10 µW
Measurement Uncertainty^c	±3% @ 1064 nm; ±5% @ 300 nm - 10.6 µm
Response Time^d	3 s (<2 s from 0 to 90%)
Housing Dimensions	76 mm x 25.2 mm x 4.8 mm (2.99" x 0.99" x 0.19")
Temperature Sensor (In Sensor Head)	N/A
Cable Length	1.5 m
Housing Features	Integrated Glass Cover Engraved Laser Target on Back
Compatible Consoles	PM400, PM100D, PM100USB, PM100A, PM101A, and PM320E

For complete specifications, please see the Specs tab.
Measured with the legacy PM200 Touch Screen Console
Defined as the measurement uncertainty during calibration at the specified wavelengths for a beam diameter > 1 mm. The ±3% specification was determined by laser calibration, and the ±5% specification was determined through spectral calibration, in which values were interpolated using the laser calibration data and the absorption curve for the absorber. Calibration can be performed at 10.6 µm upon request.
Typical natural response time (0 - 95%). Our power consoles can provide estimated measurements of optical power on an accelerated time scale (typically <1 s). See the Operation tab for additional information.

Click to Enlarge
The back of the S175C housing is engraved with the sensor specifications and a target for centering the beam on the sensor.

Designed to Measure Optical Power at the Sample Plane of a Microscope
76.0 mm x 25.2 mm Footprint Matches Standard Microscope Slides
Wavelength Range: 300 nm - 10.6 µm
Sensitive to Optical Powers from 100 µW to 2 W
Information Stored in Connector
- Sensor Data
- NIST- and PTB-Traceable Calibration Data

The S175C Microscope Slide Thermal Power Sensor Head is designed to measure the power at the sample in microscopy setups. The thermal sensor can detect wavelengths between 300 nm and 10.6 µm at optical powers between 100 µW and 2 W. The sensor head's 76.0 mm x 25.2 mm footprint matches that of a standard microscope slide and is compatible with most standard upright and inverted microscopes.

The thermal sensor has an 18 mm x 18 mm active area and is contained in a sealed housing behind a glass cover. An immersion medium (water, glycerol, oil) may be placed over the glass cover plate.

As seen in the image to the right, the bottom of the sensor housing features a laser-engraved target to aid in aligning and focusing the beam. In standard microscopes, the target can be used for beam alignment before flipping the sensor head to face the objective for power measurements. In inverted microscopes, turn on the trans-illumination lamp and align the target on the detector housing with the beam; this will center the sensor in front of the objective.

Click to Enlarge
Click Here for Raw Data
Typical absorption curve for the S175C (glass and absorber). Note that this curve is representative, and the actual absorption across the spectrum will vary from unit to unit.

Sensor specifications and the NIST- and PTB-traceable calibration data are stored in non-volatile memory in the sensor connector and can be read out by the latest generation of Thorlabs power meters. We recommend yearly recalibration to ensure accuracy and performance. Calibration may be ordered using the CAL-S200 recalibration service available below. Please contact Tech Support for more information.

The complete set of specifications are presented on the Specs tab above. Thorlabs also offers a Microscope Slide Sensor Head with a photodiode sensor for low-power, high-resolution measurements; the full presentation may be found here.

Internally SM1-Threaded Fiber Adapters

These internally SM1-threaded (1.035"-40) adapters mate terminated fiber to any of our externally SM1-threaded components, including a selection of our photodiode power sensors, our thermal power sensors, and our photodetectors.

The APC adapters have two dimples in the front surface that allow them to be tightened with the SPW909 or SPW801 spanner wrench. The dimples do not go all the way through the disk so that the adapter can be used in light-tight applications when paired with SM1 lens tubes.

For details on narrow versus wide key connectors, please see our Intro to Fiber tutorial. Please contact Tech Support if you are unsure if the adapter is mechanically compatible.

Item #	S120-FC2	S120-FC	S120-APC2^a	S120-APC^a	S120-SMA	S120-ST	S120-SC	S120-LC
Adapter Image (Click the Image to Enlarge)
Fiber Connector Type	FC/PC, 2.0 mm Narrow Key	FC/PC, 2.2 mm Wide Key	FC/APC, 2.0 mm Narrow Key	FC/APC 2.2 mm Wide Key	SMA	ST/PC	SC/PC^b	LC/PC
Thread	Internal SM1 (1.035"-40)

The S120-APC and S120-APC2 are designed with a 4° mechanical angle to compensate for the refraction angle of the output beam.
In certain angle-independent applications, this adapter may also be used with SC/APC connectors.

Based on your currency / country selection, your order will ship from Newton, New Jersey

+1 Qty Docs Part Number - Universal Price Available

S120-FC2 FC/PC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads, Narrow Key (2.0 mm)

$45.42

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S120-FC FC/PC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads, Wide Key (2.2 mm)

$45.42

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S120-APC2 FC/APC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads, Narrow Key (2.0 mm)

$35.47

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S120-APC Customer Inspired! FC/APC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads, Wide Key (2.2 mm)

$35.47

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S120-SMA SMA Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads

$45.42

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S120-ST ST/PC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads

$45.42

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S120-SC SC/PC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads

$57.07

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S120-LC LC/PC Fiber Adapter Cap with Internal SM1 (1.035"-40) Threads

$57.07

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Recalibration Service for Thermal Power and Pyroelectric Energy Sensors

Sensor Type	Sensor Item #s
Thermal Power	S175C, S302C^a, S305C^a, S310C^a, S314C^a, S322C, S350C, S370C, S401C, S405C, S415C, S425C, S425C-L, S470C
Pyroelectric Energy	ES111C, ES120C, ES145C, ES220C, ES245C

This former catalog item is now offered as a special.

Thorlabs offers recalibration services for our thermal power and pyroelectric energy sensors. To ensure accurate measurements, we recommend recalibrating the sensors annually. Recalibration of the console is included with the recalibration of a sensor at no additional cost. If you wish to recalibrate only your power meter console, please contact Tech Support for details.

The table to the right lists the sensors for which this calibration service is available. Please enter the Part # and Serial # of the sensor that requires recalibration prior to selecting Add to Cart.

Please Note: To ensure your item being returned for calibration is routed appropriately once it arrives at our facility, please do not ship it prior to being provided an RMA Number and return instructions by a member of our team. Pyroelectric energy sensors returned for recalibration or servicing must include the separate BNC to DB9 adapter, which contains the sensor EEPROM.

Sensor Type	Applications	Item #	Wavelength	Energy or Power Range	Detector Type	Aperture	Response Time
Standard Sensors	General Purpose Power Measurements	S120VC	200 - 1100 nm	50 nW - 50 mW	Si	Ø9.5 mm	<1 µs^a
		S120C	400 - 1100 nm	50 nW - 50 mW		Ø9.5 mm
		S121C	400 - 1100 nm	500 nW - 500 mW		Ø9.5 mm
		S122C	700 - 1800 nm	50 nW - 40 mW	Ge	Ø9.5 mm
Slim Sensors	Power Measurements in Tight Spaces	S130VC	200 - 1100 nm	Dual Range: 5 nW - 5 mW or 50 nW - 50 mW	Si Slim	Ø9.5 mm
		S130C	400 - 1100 nm	Dual Range: 500 pW - 5 mW or 100 µW - 500 mW	Si Slim	Ø9.5 mm
		S132C	700 - 1800 nm	Dual Range: 5 nW - 5 mW or 100 µW - 500 mW	Gi Slim	Ø9.5 mm
Microscope Slide Sensor	Measure Power at the Sample Plane of a Microscope	S170C	350 - 1100 nm	10 nW - 150 mW	Si Large Area	18 mm x 18 mm
Integrating Sphere Sensors	Power Measurements for High Powers and Divergent Beams	S140C	350 - 1100 nm	1 µW - 500 mW	Si Integrating	Ø5 mm
		S142C	350 - 1100 nm	5 µW - 5 W	Si Integrating	Ø12 mm
		S144C	800 - 1700 nm	100 nW - 500 mW	InGaAs Integrating	Ø5 mm
		S145C	800 - 1700 nm	1 µW - 3 W		Ø12 mm
		S146C	900 - 1650 nm	10 µW - 20 W		Ø12 mm
		S148C	1200 - 2500 nm	1 µW - 1 W		Ø5 mm
		S180C	2900 - 5500 nm	1 µW - 3 W	MCT (HgCdTe)	Ø7 mm
Fiber Sensors	Fiber Power Measurements and Field Applications	S150C	350 - 1100 nm	100 pW - 5 mW	Si Fiber	Ø5 mm
		S151C	400 - 1100 nm	1 nW - 20 mW	Si Fiber	Ø5 mm
		S154C	800 - 1700 nm	100 pW - 3 mW	InGaAs Fiber	Ø5 mm
		S155C	800 - 1700 nm	1 nW - 20 mW	InGaAs Fiber	Ø5 mm

Sensor Type	Applications	Item #	Wavelength	Energy or Power Range	Detector Type	Aperture	Response Time
Standard Energy Sensors	General Purpose Energy Meter	ES111C	185 nm - 25.0 µm	10 µJ - 150 mJ	Pyroelectric	Ø11 mm	N/A^d
		ES120C	185 nm - 25.0 µm	100 µJ - 500 mJ		Ø20 mm
		ES145C	185 nm - 25.0 µm	500 µJ - 2 J		Ø45 mm
High Energy Sensors	High Energy Measurements for High Peak Energy Lasers: Excimer, CO₂-TEA, and Nd:YAG	ES220C	185 nm - 25.0 µm	500 µJ - 3 J	Pyroelectric Ceramic Coating	Ø20 mm
High Energy Sensors		ES245C	185 nm - 25.0 µm	1 mJ - 15 J	Pyroelectric Ceramic Coating	Ø45 mm

Thermal Power Sensors (C-Series)

Features

Thorlabs' Thermal Power Sensors (C-Series)

High Resolution

Max Power: 10 W

Max Power: 40 W to 200 W

High Max Power Density for Pulsed Lasers

Microscope Slide Thermal Sensor

C-Series Sensor Connector

D-Type Male

Operational Principle

Natural Responses, the Sensor Time Constant, and Power Measurement Predictions

Protect Thermal Power Sensors from Thermal Disturbances

Consoles

Interfaces

Pulsed Laser Emission: Power and Energy Calculations

Power and Energy Sensor Selection Guide

Sensor Options(Arranged by Wavelength Range)

Sensor Options(Arranged by Power Range)

High Resolution

Max Power: 10 W

Max Power: 40 W to 200 W

High Max Power Density for Pulsed Lasers

Microscope Slide Thermal Sensor

Internally SM1-Threaded Fiber Adapters

Recalibration Service for Thermal Power and Pyroelectric Energy Sensors

Sensor Options
(Arranged by Wavelength Range)

Sensor Options
(Arranged by Power Range)