Embedded EEPROM Contains Sensor and Calibration Data
Post Mountable via 8-32 / M4 Universal Taps
These position sensors use thermopile sensor elements to obtain high-resolution measurements of a beam's position and power. They incorporate our OEM thermal position detectors, which consist of four sensor quadrants that calculate the beam's position by comparing the intensity measured in each quadrant. See the Operation tab for details.
The S440C detector uses the TD4HR18XP PCB-mounted thermopile sensor and is optimized for high sensitivity. The housing features four Ø6 mm through holes for compatibility with 30 mm cage systems, as well as an 8-32 / M4 universal tap for post mounting. The S442C detector incorporates the TD4HP18XA aluminum-plate-mounted thermopile sensor and can measure power levels up to 50 W. The housing includes a heat sink for superior heat dissipation, as well as two 8-32 / M4 universal taps for post mounting.
For information on recalibration services for these products, please contact Tech Support.
Compatible Power Meter Console and Power Meter Interfaces Both detectors feature C-Series connectors and can be controlled using either the PM400 power meter console or the PM102 series power meter interfaces (all control units sold separately). The PM400 console features a touchscreen display for the power and position readout. The PM102 series requires a PC with the OPM software in order to operate the sensor in a power meter system; depending on the PM102 model used, operation can be through USB 2.0, RS-232, or UART.
There are a number of different display options that can be viewed either on the PM400 console display screen or in the OPM software GUI:
Position Tuning: a visual representation of the beam's location on the sensor. The visible area can be adjusted between a centered Ø1 mm circle and Ø6 mm circle. The left side shows the power measured by the entire sensor surface and the X and Y coordinates of the beam. An optional setting can show a visual trace of the position over time (Position Trace Display).
Graph: a graph of the X and Y positions over time, or a graph of total power over time. The user can touch a single button to toggle between the position and power graphs.
Statistics: a table of measurement statistics. The unit takes a number of sequential samples and then displays the mean, median, standard deviation, and more.
Numerical: a digital readout of the overall power measurement for the entire sensor, displayed in W, V, or dB. The beam position coordinates are also shown in the upper right of the screen.
Click to Enlarge Click Here for Raw Data The wavelength range of the data in this graph is limited by the detector used during testing. The thermal position detectors are capable of operating at up to 20 µm.
190 nm - 20 µm
Optical Power Working Range
0.5 mW - 5 W
10 mW - 50 W
Max Average Power Densitya
Max Pulse Energy
0.3 J/cm2 (1 ns Pulse) 5 J/cm2 (1 ms Pulse)
±5% at 1064 nm; ±7% for 250 nm - 17 µm
50 µm (1 mm Circle); 200 µm (6 mm Circle)
100 µm (1 mm Circle); 300 µm (6 mm Circle)
15 µm (1 mm Circle); 100 µm (6 mm Circle)
25 µm (1 mm Circle); 150 µm (6 mm Circle)
Coating / Diffuser
High Power Broadband
Head Temperature Measurement
17 mm x 17 mm
40.6 mm x 40.6 mm x 8.9 mm (1.60" x 1.60" x 0.35")
100.0 m x 100.0 mm x 57.8 mm (3.94" x 3.94" x 2.28")
D-Sub-9 Pin Male
8-32 / M4 Universal Tap, 30 mm Cage Rod Through Holes
Two 8-32 / M4 Universal Taps, SM1 (1.035"-40) Internal Thread, Externally Threaded SM1 Coupler Included
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.
Measured Using the PM400 Console with the Acceleration Circuit Switched Off
Beam Diameter > 1 mm
Valid within the Specified Area at the Center of the Sensor
Typical Natural Response (0 - 95%)
Click to Enlarge Figure 1: 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.
These thermal power detectors are based on thermopile sensors. The top layer of the sensor, which appears gray in color, consists of a light-absorbing material. Located immediately behind the sensor, and in thermal contact with it, is a layer containing multiple thermocouples. Thermocouples are made by bringing two dissimilar metals into contact, and their point of contact is called a junction. The other side of the thermocouple layer must be thermally coupled to 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. This axial (or matrix) configuration of thermocouples is diagrammed in Figure 1.
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 the adjacent junctions placed close to the heat sink. This arrangement takes advantage of the thermoelectric (Seebeck) effect, in which a temperature difference between adjacent junctions generates a proportional voltage difference. By connecting multiple thermocouples in series, the magnitude of the generated voltage is increased.
Axially-configured sensors such as the thermal quadrant detectors on this page can achieve high resolutions in the microwatt range while providing relatively fast response times. These sensors detect optical powers up to 50 Watts, which is limited mostly by the thickness of the absorbing material.
Figure 2: The sensor area consists of four thermopile sensors arranged as quadrants of a square.
Quadrant Detector Beam Position Calculation Each thermal position detector consists of four individual thermopile sensors arranged in a 2 x 2 matrix, as shown in Figure 2. The quadrants are mechanically coupled by one aluminum plate but electrically isolated; thus, heat is free to flow across the entire active area, but the signal from each quadrant measures the response in only that quadrant's thermopile. The beam's coordinates X and Y are calculated using the voltage outputs of all four detectors:
where V1, V2, V3, and V4 are the output voltage signals from Q1, Q2, Q3, and Q4, respectively, in Figure 2. Since the sensor response is nonlinear, the detector uses a calibration factor for each axis, Calx and Caly, to calculate the absolute position.
Click to Enlarge Figure 3: Natural Response of the S440C and S442C Detectors. The dotted line is at 0.99 and the red square indicates 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 a thermal sensor is its measured response to being instantaneously and steadily illuminated after being held in total darkness. This step function illumination stimulus produces a measured response that can be modeled using an exponential function and is similar to the function describing the rate at which a capacitor charges. Figure 3 shows the natural response measured for the thermal position sensing detectors.
The sensor time constant is defined in terms of how long it takes for the sensor response to reach 99% of its maximum response. The definition used by Thorlabs' power meter consoles is that 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.
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.
C-Series Sensor Connector
D-Sub-9 Pin Male
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.
Digital Power and Energy Measurements, Touchscreen Control
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)
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
Source Spectral Correction
External Trigger Input
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
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)
10 Hz (Numerical) 25 Hz (Analog Simulation)
Mechanical Analog Needle
Simulated Analog Needle
LiPo 3.7 V 1300 mAh
LiPo 3.7 V 2600 mAh
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.
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 EnergySensors: 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.
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.
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.