Thermal Sensors

Ideal for measuring the average power from high power lasers

Thermal sensors are best suited for measuring CW laser power, average power in pulsed lasers or the energy of long pulses. A variety of thermal sensors is offered to suit different powers, beam size (etc). Thermal sensors (also called thermopiles) work over an extremely broad spectral range, as well as over a wide range of input powers. Thermal sensors also offer very uniform spatial response and are unaffected by changes in beam size, position or uniformity. Thermal sensors have uncompensated response times on the order of 1-45 seconds, depending upon sensor size. Electronic compensation within most meters results in 1-10 second response times. Thermal sensors are offered with a choice of apertures up to 200mm and are cooled by conduction, convection, forced air (fan cooling) or water cooling.

Thermopile sensors are compatible with all power and energy meter displays. Please note that the beam position capability of LM-series thermal sensors can only be utilised when connected to a LabMax meter. Selected thermopile heads are also available as PowerMax-USB sensors with the power meter electronics reduced in size to a USB connector.

Thermopile heads are offered with a choice of surface and volume absorbing sensors. Surface absorbing thermopile sensors are coated with a choice of finishes to suit different laser types:

• Black – this coating is applied to the high sensitivity, amplified thermopile sensors
• Broadband – this coating is applied to most of the air, fan and water-cooled sensors and possesses a higher damage threshold for both pulsed and CW lasers
• Excimer (UV) – this coating is optimised for use with excimer lasers
• HTD / H – the broadband coating applied to the quadrant, position sensing thermopile sensors

Volume absorbing thermopile sensors are fitted with a special diffuser to withstand the high peak powers from Q-switched or other high peak power lasers.

The relatively slow response of thermal sensors renders them unsuitable for measuring the energy per pulse from repetitively pulsed lasers. Instead, thermopile sensors can be used for measuring the average power from such lasers. For lasers which emit a single, long pulse, thermal sensors can be used to measure the energy from the pulse in Joules. For an explanation of this, download the technical note on measuring long pulse energy.

High Sensitivity Thermopile Sensors

The PS-series sensors offer a thermally stabilised, amplified power sensor with a broad spectral response, high sensitivity, and large active area. These sensors are ideal for laser diodes, diode bars and stacks, HeNe, HeCd and small ion lasers. For optimum performance at low power levels we recommend the PS10Q and PS19Q, which utilise quartz windows. PS10 models include a detachable beam tube to block stray light. Fibre optic connectors are available as accessories.

Accessories for Coherent high sensitivity thermopile sensors are listed in the table below.

Air-Cooled Thermopile Sensors (up to 150W)

The air cooled thermopile sensors are designed for use with low-to-medium powered CW and pulsed lasers from 10mW to 150W average power output. These sensors are able to dissipate the incident laser energy via convection cooling which makes them convenient to setup and use. Within this family of sensors you can select between a broadband or DUV excimer detector coating. The former offers uniform spectral response from 190nm to 11.0μm, while the excimer coating is optimised for use from 157nm to 351nm. The PM-10 and PM-30 are available with selected meters at reduced prices as part of Coherent's power meter value package programme

Water-Cooled Thermopile Sensors (up to 150W)

These compact, block sensors are ideal when space is an issue. They must be water-cooled to achieve the continuous, full power rating, but they can also be mounted on a heat-sink or as stand alone sensors for intermittent application of power. These models incorporate cables for attachment to our meters. OEM versions of these sensors are also offered; OEM versions include either a BNC or 4-pin connector to facilitate use in an embedded setting within a laser system.

Fan-Cooled Thermopile Sensors (up to 300W)

These fan-cooled thermopiles bridge the gap between the air-cooled and water-cooled sensors. They are an excellent choice when the use of water cooling is not desirable. A compact, wall-mount power supply provides the 12V DC required to drive the fan.

High Power Water-Cooled Thermopile Sensors (up to 10kW)

Most lasers above 300W will require one of these thermopile sensors that require water cooling at all times. A post and stand are included with each sensor.