CONEX-PSD
Two-Axis Position & Power Sensing Device
4.0
Optimizing Measurements
This section provides general recommendations for improving light measurement
setups.
4.1
Avoid Stray Light
As the sensitive area of a PSD is relatively large (81 mm
2
for Si, 100mm² for Ge), it
may collect unwanted light on top of the beam being measured. This may affect the
measurement accuracy.
PSD’s are also sensitive to a large spectral range (300 to 1100 nm for Si and 800 to
1700 for Ge). Although the light to be measured might be centered on one particular
wavelength, sensor will be affected by other wavelengths.
For example, stray light can easily reach 10 μW/mm
2
on a broad spectral range in a
room. This might not be negligible, especially if a large gain was set in the controller.
There are 2 ways to minimize the effect of stray light:
•
Shield the sensor from unwanted light.
•
Block the unwanted wavelength.
4.1.1
Shielding the Sensor
To minimize this effect, it is recommended to shield the sensor from stray light.
One or several Newport filter holders can be used for that.
4.1.2
Filtering and Attenuation
Several types Newport filter can be mounted on the Newport “Model 883-OH 1" filter
holder.
For example:
Absorptive Neutral Density Filter (FSR-xxxx):
9
EDH0315En1030 — 07/16
