Thermal Power Sensors - THORLABS PM100D Operation Manuals

4.2 Controlling the PM100D

4.2.4.2 Thermal Power Sensors

The PM100D is compatible to the Thorlabs S300C series thermal power sensors.
The sensor will be ready to operate few seconds after plugging to the DB9 connector.
Attention
Refer to the sensor data sheet and pay attention to the optical
damage threshold!
Exceeding these values will permanently destroy the sensor!
Thermal sensors absorb the incident laser power, whereby the developing heat gets
turned into a small voltage caused by heat flow through thermocouple elements
between absorbing area and sensor heat sink. Thorlabs offers with its S3xxC series
thermal sensors that cover a wide range of applications. The sensors are available
with different coatings. Black broad band coating as absorber does not need a
wavelength correction because the response is nearly flat from the UV to the mid-IR.
Special hard coatings can withstand high power levels and show also a good spectral
flatness. Further Thorlabs offers special heads for Excimer lasers with large beam
diameters and short pulse lasers with coatings for very high peak power levels.
The output voltage of a thermal sensor is linear to the incident laser power, as long
the thermal system is properly zeroed. The main application area for thermal sensors
is the measurement of high power levels from 100mW. Thorlabs offers also a special
thermally isolated thermal head with flat response and on power levels starting in the
µW range.
4.2.4.2.1 Readout acceleration
Thermal sensors show a fairly slow response. When laser power hits the active area
it takes, depending on the sensor type, from some 1 up to 20 seconds until the
system has settled and the power reading shows the right value.
Through special circuitry this time can be shortened to approximately 1-3 seconds by
'predicting' the final power value. The PM100D automatically uses the right
adjustment of the electronics to the time constant of the thermal sensor.
Nevertheless this circuitry has the disadvantage of inducing some noise to the
measurement value. Therefore the acceleration circuit can be disabled / enabled in
the Meas Confi g measurement configuration menu by the Acc AUTO/ON/OFF
button
.
In 'AUTO' mode the accelerator will switch on when a power change larger than 5%
of the measurement range is detected and switch off after 5 times of the time
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