Gentec-EO PH - Manual (Page 14)

Version 2.3
PH Series Instruction Manual Gentec Electro-Optics Inc. All rights reserved
10
Set Diode Zero or Zero Offset or Offset
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3 DAMAGE TO THE OPTICAL ABSORBER MATERIAL
Damage to the optical absorber material is usually caused by exceeding the manufacturer's specified
maximum incident in the average power density.
Refer to the specifications pages for the PH Series power head specifications.
Cleaning: Use Alcohol and a clean cotton cloth.
4 ERROR SOURCES
The photodiode and monitor are NIST traceable. Several errors source may affect your
measurements.
4.1 OFFSET
Zero the offset before any measurement as described in Section 2.2 above. Otherwise all
measurements will include a component not related to the laser power. This will add a systematic
error to absolute power measurements. This error may disappear from relative power
measurements. When you subtract two measurements made under identical conditions, the offset in
the second measurement cancels the offset in the first if they are identical. We recommend zeroing
the offset for all measurements to eliminate any drift that occurs between measurements.
4.2 OFFSET DRIFT DUE TO TEMPERATURE
The Photodiode Shunt Resistor is sensitive to temperature, this affects the offset value. When
making very low power level measurements, allow your system to warm up for 30 minutes or until the
offset power is stable for several minutes. The sensitivity of the phodiode also has temperature
dependence. See Fig 1-2 and Fig 1-3 for the typical temperature sensitivity dependence over the
spectral range for Ge, Si and SiUV.