William Angerer - Department of Physics and Astronomy - University ...

chopper
AGate
B Gate
Signal
Figure 7.5: Relationship between the optical chopper and photon counter gates. The
count rate from the signal, which is detected only when the chopper is open. is much
larger than the background count, which is always detected.
from the P:\IT with a Stanford Research Systems gated photon counter model SR-lOO.
The gated photon counter is an integrated photon counting system that consists of
amplifiers. discriminators, gate generators, and counters. The dual channel photon
counter has a variety of counting modes including synchronous detection ('-\-B counting).
In synchronous detection, an optical chopper modulates a light source. During
the experiment, the reference output from the optical chopper triggered the gates of
the photon counter. The A Gate of the photon counter was positioned to coincide
with the open phase of the chopper. This is displayed in Fig. 7.5. Similarly. the
B Gate of the photon counter was positioned to coincide with the closed phase of
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