Thorlabs S302C Thermal Power Sensor Head, 0.19-25 µm, 2 W

Overview

The Thorlabs S302C is a thermally isolated thermal power sensor head for Thorlabs optical power meter consoles. It is designed for low power measurements with very low drift and high resolution, and it covers an exceptionally wide spectrum, from 190 nm in the ultraviolet to 25 µm in the far infrared. Because its broadband absorber responds almost equally at all wavelengths, the Thorlabs S302C is the right choice for light sources with broad or uncertain spectra, such as amplified spontaneous emission sources, LEDs, filament lamps and swept lasers, where photodiode sensors give misleading readings due to their strong wavelength dependency. It measures continuous power from 100 µW up to 2 W with a resolution of 1 µW.

Seven Star LLC supplies the Thorlabs S302C to university physics and chemistry laboratories, laser application centres, telecom and fibre workshops and industrial quality laboratories across Oman and the GCC. Our Muscat team helps customers match the sensor to a suitable console and fibre adapter, and supports annual recalibration planning.

Measurement Principle

A thermal sensor measures optical power by converting light into heat. In the Thorlabs S302C, incoming radiation is absorbed by a black broadband coating on a thermally isolated absorber. The absorbed power raises the absorber temperature relative to a reference, and the resulting temperature difference signal, proportional to the absorbed power, is read by the console. Since almost all incident light is absorbed regardless of wavelength, the response is flat across the spectrum and back reflection from the black coating is negligible. This is the key advantage over photodiodes, whose responsivity changes strongly with wavelength.

The same principle explains the main limitations. Thermal sensors respond more slowly than photodiodes; the spec sheet gives a response time of about 3 seconds from 0 to 90 percent with the PM100D console. They are also sensitive to air currents and other thermal disturbances, so the sensor must be zeroed before a measurement and shielded from drafts. For pulsed lasers, the thermal head reads average power, and peak power may exceed the rated maximum provided the pulse energy density remains below the damage threshold.

Engineering Design of the Thorlabs S302C

The Thorlabs S302C has a 12 mm diameter detector set 15 mm behind the front face, inside a housing of 40 mm diameter and 41 mm length, or 44 mm with the adapter. Cooling is by natural convection, and insulation inside the head provides thermal stabilisation. The front adapter carries an external SM1 thread that accepts S120 series fibre adapters, including FC, SMA, SC, LC and ST types, so fibre-coupled sources can be measured directly. An M4 post of 60 mm is included and the head fits standard Thorlabs posts and post holders. The sensor weighs 0.2 kg.

A 1.5 m cable ends in a Sub-D 9-pin male connector with non-volatile memory. This memory stores the sensor information and its NIST and PTB traceable calibration data, so a compatible console recognises the head automatically and applies the correct calibration. Calibration uncertainty is plus or minus 3 percent at 1064 nm and plus or minus 5 percent from 190 nm to 25 µm, with linearity of plus or minus 1 percent. Thorlabs recommends yearly recalibration starting one year after purchase.

Key Features

The Thorlabs S302C spec sheet highlights the following features.

• Flat spectral response from 190 nm to 25 µm thanks to a broadband BBF coating.
• Continuous power range of 100 µW to 2 W with 1 µW resolution and very low drift.
• Maximum intermittent power of 2.5 W for up to 2 minutes and 200 W/cm² maximum average power density.
• Pulse energy density limits of 0.2 J/cm² at 1 µs and 2 J/cm² at 1 ms.
• Calibration uncertainty of plus or minus 3 percent at 1064 nm and linearity of plus or minus 1 percent.
• NIST and PTB traceable calibration data stored in the connector memory.
• SM1 threaded adapter for S120 series FC, SMA, SC, LC and ST fibre adapters.
• Compatibility with PM100D, PM100A, PM100USB, PM200, PM400 and PM320E consoles.

Industrial Applications

Thermal sensors are essential wherever the wavelength is broad, unknown or outside the range of photodiodes. In research laboratories in Muscat and across the GCC, the Thorlabs S302C measures CO2 laser power in the mid infrared, characterises LED and lamp output for lighting and photobiology studies, checks average power of pulsed Nd:YAG and diode lasers, and verifies the output of broadband ASE and supercontinuum sources. Students benefit from a single sensor that works across ultraviolet, visible and infrared experiments.

In industry, the Thorlabs S302C supports quality checks on laser marking and engraving systems, fibre amplifier testing in telecom workshops, and verification of optical sources used in gas analysers and spectroscopic instruments in the oil and gas sector. Seven Star LLC supplies the sensor together with Thorlabs consoles and fibre adapters, and our Muscat engineers help laboratories in Oman and the GCC select between thermal and photodiode sensors for each task. As a general rule, a photodiode head is preferred for low power, narrowband sources where speed and sensitivity matter, while the Thorlabs S302C is preferred where spectral flatness, higher power or broadband content matter more than response time.

Technical Specifications

The following Thorlabs S302C data is taken from the Thorlabs spec sheet (document 18368-S01).

How to Order

To request a quotation for the Thorlabs S302C, contact Seven Star LLC with the quantity, console model and any fibre adapters required. Our Muscat instrumentation division confirms availability, provides the Thorlabs spec sheet and supports laboratories in Oman and the GCC with recalibration planning. Related Thorlabs products include the Thorlabs PM100D power and energy meter console, the Thorlabs PM400 touchscreen power meter console and the Thorlabs PM100USB power meter interface.