Photodiode Sensors - OPHIR vega User Manual

Operation with Photodiode Type Sensors
Warning:
Before using the sensor for power measurement,
check that your laser power or energy and energy
density does not exceed the sensor ratings. See
Table 5. and Table 6. in Chapter 10.

5.1 Photodiode Sensors

When a photon source, such as laser, is directed at one
of the PD300 or 3A-IS series photodiode detectors, a
current is created proportional to the light intensity and
dependent on the wavelength.
The PD300 and PD300-3W sensors have a unique dual
detector sensor (patented) in which the two detectors are
identical and connected back to back. When a uniform
signal, such as room light background, falls on the
detector sensor the signal from the two detectors
cancels.
On the other hand, when a laser beam falls on the sensor,
it illuminates only the first detector and therefore is
detected.
background while detecting the desired signal.
subtraction is not perfect but usually 98% of the
background signal is eliminated so the detector can
usually be used in ordinary laboratory lighting conditions.
The Vega display unit amplifies this signal and indicates
the power level received by the sensor. Due to the
superior circuitry of the Vega, the noise level is very low,
and the PD300 /3A-IS series sensors with the Vega
display have a large dynamic range from nanowatts to
hundreds of milliwatts.
Since many low power lasers have powers on the order
of 5 to 30mW, and most photodiode detectors saturate at
about 2mw, most sensors of the PD300 series have been
constructed with a built in filter so the basic sensor can
Chapter 5.
Thus the PD300 subtracts most of the
59
The