Recommendations - THORLABS APD110 Series Operation Manual

APD110x/120x

3.4 Recommendations

Please always remember that the Avalanche Photodetectors are extremely sensitive devices.
Carefully shielding the Avalanche Photodetectors from any unwanted light sources is essential.
Common techniques include baffling or other opaque barriers like black cloths or lens tubes.
It is highly recommended to use appropriate band pass filters in front of the detector to mini-
mize the influence of stray light.
Since stray light has its strongest frequencies at DC and line frequency or harmonics, optical
chopping and Lock-In detection can further improve measurement sensitivity.
It is not necessary to switch off the Avalanche Photodetectors when it is exposed to ambient
light. The amplifier will saturate but unlike Photomultiplier Tubes it will not be damaged or satur-
ated for a long period of time.
Another critical point can be electrostatic coupling of electrical noise associated with ground
loops. In most cases an electrically isolated post (see Thorlabs parts TRE or TRE/M) will sup-
press electrical noise coupling. You should always try to identify the electrical noise sources
and increase the distance to the Avalanche Photodetector. If possible, you can also rotate the
Avalanche Photodetector input away from the noise source. Different common ground points
can also be tested.
The amplifier offset voltage is factory set to zero at 23°C ambient temperature. Due to the
very high transimpedance gain, even small temperature changes may affect offset voltage.
Therefore it is recommended to use the Avalanche Photodetector in a constant temperature
environment after a short warm up period (~5min) for exact DC light level measurements.
The M factor is factory set at 23°C ambient temperature. As APD110x/120x are operated at a
fixed internal reverse bias voltage and not temperature-compensated, their actual M factor will
change with ambient temperature. So it is recommended to operate the APD110x/120x always
at 23°C ambient temperature for exact measurement results. Please see section M Factor
Temperature Dependency for typical curves of M factor vs. ambient temperature.
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