Thermal Power Sensors (C-Series)

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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.

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S401C Connected to the PM100D Console

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-THPY).

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.

• 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

For details on sensor-related terminology, see our list of definitions.

High Resolution

• 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

• 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

• 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.

Operational Principle

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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.

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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.

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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	PM5020
(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 Power, Thermal Power, and Pyroelectric Energya	Photodiode Power, Thermal Power, Thermal Power and Position, and Pyroelectric Energya	Photodiode Power, Thermal Power, Thermal Power and Position, and Pyroelectric Energy
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)	9.97" x 4.35" x 11.56" (253.2 mm x 110.6 mm x 293.6 mm)
Channels	1			2
External Temperature Sensor Input (Sensor not Included)	-	-	Readout and Record Temperature Over Time	Readout and Record Temperature Over Time
External Humidity Sensor Input (Sensor not Included)	-	-	Readout and Record Humidity Over Time	Readout and Record Humidity Over Time
Input/Output Ports	-		4 GPIO, Programmable	4 Configurable Digital I/O Channels
Shutter Control	-	-	-	Support for SH05R(/M) or SH1(/M) Optical Shutter with Interlock Input
Fan Control	-	-	-
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
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)	4.32" x 2.43" (109.7 mm x 61.6 mm)
Refresh Rate	20 Hz		10 Hz (Numerical) 25 Hz (Analog Simulation)	25 Hz
Measurement Viewsb
Numerical
Mechanical Analog Needle		-	-	-
Simulated Analog Needle	-
Bar Graph	-
Trend Graph	-
Histogram	-		-	-
Statistics
Memory
Type	-	SD Card	NAND Flash	SD Card
Size	-	2 GB	4 GB	8 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	Line Voltage: 100 - 240 V

• As the PM100D and PM400 consoles can only support repetition rates of up to 3 kHz, they should not be used with the ES408C sensor, which detects repetition rates up to 10 kHz.
• These are the measurement views built into the unit.

Interfaces

Item #	PM101	PM102	PM103	PM101A	PM102A	PM103A
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Operation Protocol	USB, RS232, UART, and Analog			USB and Analog SMA
Sensor Compatibility
Photodiode		-			-
Thermal Power			-			-
Thermal Position & Power	-		-	-		-
Pyroelectric	-	-		-	-

Key Features
C-Series Sensor DE-9 Connector
USB Connector	Lockable			Lockable
USB Max Measurement Speed	1000 S/s	1000 S/s	100 000 S/s	1000 S/s	1000 S/s	100 000 S/s
Serial DE-9 Connector	-			-
DE-9 Max Measurement Speed	-			-
SMA Connector(s)	-			1 Analog Power Output	3 Ports: Power, X-Position, and Y-Position	3 Ports: AO1, AO2, and Digital I/O (Configurable as External Trigger Input)
DA-15 Universal Connector with 2 Auxiliary I/O Ports			GPIO Ports Also Configurable as Trigger Input (Pin 2) or for Pass/Fail Analysis (Pin 3)	-
DA-15 Max Measurement Speed	200 S/s	200 S/s	100 000 S/s	-
Ethernet (RJ45) Connector	-	-	-	-
Ethernet Max Measurement Speed	-	-	-	-
Phoenix DMC 0,5/7 Connector	-	-	-	-
DMC 0,5/7 Max Measurement Speed	-	-	-	-
External Temperature Sensor Input (Sensor Not Included)	NTC Thermistor			-
Display
Type	No Built-In Display; Controlled via GUI for PC
Measurement Viewsc
Numerical	Requires PC
Simulated Analog Needle	Requires PC
Bar Graph	Requires PC
Trend Graph	Requires PC
Histogram	Requires PC
Statistics	Requires PC
Memory
Type	Internal Non-Volatile Memoryfor All Settings
Power
External	5 VDC via USB or 5 to 36 VDC via DA-15 Pins 1 and 9			5 VDC via USB

Item #	PM103E	PM101R	PM101U	PM102U	PM103U	PM100USB
(Click Photo to Enlarge)
Operation Protocol	Ethernet, RS232, and Analog	USB and RS232	USB Operation			USB
Sensor Compatibility
Photodiode				-
Thermal Power					-
Thermal Position & Power		-	-		-	-
Pyroelectric		-	-	-		a

Key Features
C-Series Sensor DE-9 Connector
USB Connector	-	Lockable	Lockable			Not Lockable
USB Max Measurement Speed	-	1000 S/s	1000 S/s	1000 S/s	100 000 S/s	300 S/s
Serial DE-9 Connector	-		-			-
DE-9 Max Measurement Speed	-	200 S/s	-			-
SMA Connector(s)	-	-	-			-
DA-15 Universal Connector with 2 Auxiliary I/O Ports	-	-	-			-
DA-15 Max Measurement Speed	-	-	-			-
Ethernet (RJ45) Connector		-	-			-
Ethernet Max Measurement Speed	100 000 S/s	-	-			-
Phoenix DMC 0,5/7 Connector		-	-			-
DMC 0,5/7 Max Measurement Speed	100 000 S/s	-	-			-
External Temperature Sensor Input (Sensor Not Included)	NTC Thermistor	-	-			-
Display
Type	No Built-In Display; Controlled via GUI for PC
Measurement Viewsc
Numerical	Requires PC
Simulated Analog Needle	Requires PC
Bar Graph	Requires PC
Trend Graph	Requires PC
Histogram	Requires PC
Statistics	Requires PC
Memory
Type	Internal Non-Volatile Memory for All Settings					-
Power
External	Power over Ethernetd and 5 to 36 VDC via DMC 0,5/7 pin 1 and 2	5 VDC via USB	5 VDC via USB			5 VDC via USB

• As the PM100USB interface can only support repetition rates of up to 3 kHz, it should not be used with the ES408C sensor, which detects repetition rates up to 10 kHz.
• 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 Monitor Software.
•  48 V is the nominal voltage over the network, but can range from 36 V - 57 V.

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 is 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	Description
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	Pavg	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	Ppeak	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	frep	Hertz [Hz]		The frequency with which pulses are emitted. Equal to the reciprocal of the period.

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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	PM5020	PM101 Series	PM102 Series	PM103 Series	PM100USB
Photodiode Power						-
Thermal Power							-
Thermal Position	-	-			-		-	-
Pyroelectric Energy	-	a	a		-	-		a

• As the PM100D and PM400 consoles and the PM100USB interface can only support repetition rates of up to 3 kHz, they should not be used with the ES408C sensor, which detects repetition rates up to 10 kHz.

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.

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 µsa
		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 such as 30 mm Cage Systems	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		Ø9.5 mm
		S132C	700 - 1800 nm	Dual Range: 5 nW - 5 mW or 100 µW - 500 mW	Ge Slim	Ø9.5 mm
Compact Slim Sensor	Power Measurements in Tight Spaces such as 16 mm Cage Systems	S116C	400 - 1100 nm	20 nW - 50 mW	Si Compact Slim	Ø6 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
		S171C	400 - 1100 nm	1 nW - 15 mW
	Measure Relative Peak Power at the Sample Plane of a Microscope	NS170C	780 - 1300 nm	0.5 W - 350 mWb	Si Large Area with Second-Order Nonlinear Crystal	Ø4.5 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		Ø12 mm
		S142CL	400 - 1100 nm	10 µW - 5 W	Si Integrating w/Baffle	Ø22 mm
		S144C	800 - 1700 nm	100 nW - 500 mW	InGaAs Integrating	Ø5 mm
		S145C	800 - 1700 nm	1 µW - 3 W		Ø22 mm
		S145CL	800 - 1700 nm	10 µW - 3 W	InGaAs Integrating w/Baffle	Ø22 mm
		S146C	900 - 1650 nm	10 µW - 20 W	InGaAs Integrating	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		Ø5 mm
		S154C	800 - 1700 nm	100 pW - 3 mW	InGaAs Fiber	Ø5 mm
		S155C	800 - 1700 nm	1 nW - 20 mW		Ø5 mm

Sensor Type	Applications	Item #	Wavelength	Energy or Power Range	Detector Type	Aperture	Response Timec
High Resolution	Broadband Measurements of Optical Powers ≤5 W with 1 µW or 5 µW Resolution	S401C	190 nm - 20 µm	10 µW - 1 W (3 Wd)	Thermal Surface Absorber with Background Compensation	Ø10 mm	1.1 s
		S405C	190 nm - 20 µm	100 µW - 5 W	Thermal Surface Absorber	Ø10 mm	1.1 s
Max Power: 10 W	General Broadband Power Measurements of Low and Medium Power Light Sources	S415C	190 nm - 20 µm	2 mW - 10 W (20 Wd)		Ø15 mm	0.6 s
		S425C	190 nm - 20 µm	2 mW - 10 W (20 Wd)		Ø25.4 mm	0.6 s
Max Power: 40 W to 200 W		S350C	190 nm - 1.1 µm, 10.6 µm	10 mW - 40 W (60 Wd)		Ø40 mm	9 s (1 s from 0 to 90%)
		S425C-L	190 nm - 20 µm	2 mW - 50 W (75 Wd)		Ø25.4 mm	0.6 s
		S322C	250 nm - 11 µm	100 mW - 200 W (250 Wd)		Ø25 mm	5 s (1 s from 0 to 90%)
High Max Power Density	Optical Power Measurements of Nd:YAG and Other Pulsed Laser Sources	S370C	400 nm - 5200 nm	10 mW - 10 W (15 Wd)	Thermal Volume Absorber	Ø25 mm	45 s (3 s from 0 to 90%)
		S470C	250 nm - 10.6 µm	100 µW - 5 W		Ø15 mm	6.5 s (<2 s from 0 to 90%)
Microscope Slide	Measure Power at the Sample Plane of a Microscope	S175C	300 nm - 10.6 µm	100 µW - 2 W	Thermal Surface Absorber	18 mm x 18 mm	3 s (<2 s from 0 to 90%)

Sensor Type	Applications	Item #	Wavelength	Power Range	Detector Type	Aperture	Response Timec
High Resolution	Precise Beam Position and Power Measurements of Low and Medium Power Lasers	S440C	190 nm - 20 µm	0.5 mW - 5 W	Thermal Absorber, Four Quadrants	17 x 17 mm	<1.1 s
High Power		S442C	190 nm - 20 µm	10 mW - 50 W	Thermal Absorber, Four Quadrants	Ø17.5 mm	<0.6 s

Sensor Type	Applications	Item #	Wavelength	Energy or Power Range	Max Repetition Rate (@ 1 MΩ Load)	Detector Type	Aperture	Response Time
Standard Energy Sensors	General Purpose Energy Meter	ES111C	185 nm - 25 µm	10 µJ - 150 mJ	40 Hz	Pyroelectric Black Broadband Coating	Ø11 mm	N/Ae
		ES120C	185 nm - 25 µm	100 µJ - 500 mJ	30 Hz		Ø20 mm
		ES145C	185 nm - 25 µm	500 µJ - 2 J	30 Hz		Ø45 mm
High-Energy Sensors	High Energy Measurements for High Peak Energy Lasers: Excimer, CO2-TEA, and Nd:YAG	ES220C	185 nm - 25 µm	500 µJ - 3 J	30 Hz	Pyroelectric Ceramic Coating	Ø20 mm
		ES245C	185 nm - 25 µm	1 mJ - 15 J	30 Hz		Ø45 mm
Fast Energy Sensors	High Repetition Rate Measurements	ES308C	185 nm - 25 µm	500 µJ - 1 J	1 kHz	Pyroelectric Black Broadband Coating	Ø8 mm
		ES312C	185 nm - 25 µm	100 µJ - 1 J	250 Hz		Ø12 mm
		ES408C	185 nm - 2.5 µm	100 µJ - 1 J	10 kHz	Pyroelectric Metal Coating	Ø8 mm
		ES412C	185 nm - 2.5 µm	50 µJ - 500 mJ	2 kHz		Ø12 mm

• 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.
• The power range provided is for lasers with a repetition rate of 80 MHz. Because the peak power and peak power density are dependent on the average power and repetition rate of the laser, the upper limit to the working average power range will be lower for lower repetition rates. Please see the Specs tab here for more details. 
• 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 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. Please see the Specs tab here for the τ value of each sensor.

Sensor Options
(Arranged by Wavelength Range)

Sensor Options
(Arranged by Power Range)