Measurement Considerations; Choosing The Right Sensor - THORLABS PM100USB Operation Manual

PM100USB

6 Measurement Considerations

6.1 Choosing the Right Sensor

The optimal choice of sensor depends on several factors, starting with the type of light source
to measure (wavelength and power) and the application. No single sensor can cover all applica-
tions. The table below provides guidance to find an optimal power sensor type depending on
the light source. Be aware that within each sensor group there are special models best suitable
for specific applications. For advice on selecting a sensor, please contact the engineers at
Thorlabs .
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Photodiode Sensors
Thorlabs offers photodiode sensors of the C-series
20 W that show advantages in sensitivity, stability and drift when compared to thermal sensors.
The sensors are built as a combination of a photodiode with either a neutral density filter or a
integrating sphere. They provide linearity over several orders of magnitude. For sensors which
can handle small power levels down to the pW range, the sensor size can be reduced to a min-
imum. Further, the response time of such sensors is very fast down to the nanosecond range.
Thermal Sensors
Thermal sensors absorb incident laser power. This heats up the absorber and the heat flow
through thermocouple elements between absorbing area and sensor heat sink generates a
small voltage. Thorlabs
range of applications and are available with different coatings.
· Black broad band coatings: Depending on the sensor and operating wavelength,
wavelength correction may not be required because the response is nearly flat from the
UV to the mid-IR for some sensors. Please see the respective sensor manual.
· Special hard coatings: These high power broadband sensors withstand high power
levels and show a good spectral flatness.
· Thorlabs offers special heads for power measurements with volume absorber coatings
for high peak power levels (e.g. YAG Lasers).
The output voltage of a thermal sensor is linear proportional 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 up. Thorlabs offers also a special thermally
isolated thermal head with flat response and on power levels starting in the µW range.
Power Sensors:
Light Source
Diode Lasers UV - NIR
Diode Lasers NIR
High Power Fiber Lasers
ASE Sources
Femtosecond Lasers
Gas Lasers
Excimer Lasers
YAG Lasers
LEDs
Pyroelectric Sensors
14
C-Series thermal power sensors
Photo Diode Sensor
Si Ge
+++ +
- +
- -
- -
- +
++ -
- -
- -
+ -
for power levels from sub-nano watts up to
(S3xxC, S4xxC, S175C) cover a wide
Thermal Sensors
InGaAs BB
- ++
+++ ++
++ ++
++ ++
++ ++
- ++
- -
- -
- +++
HPB Volume
- -
- -
++ -
- -
+ -
+ -
+++ +
+ +++
+ -
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