Noise cancelling circuitry for optical systems with signal divid

Details Noise cancelling circuitry for optical systems with signal divid Noise cancelling circuitry for optical systems with signal divid

1990-10-09

1992-07-28

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

250575, 250345, H01J 4014

Patent

active

051342766

ABSTRACT:
A noise suppression system is described for use with a laser measurement system in which a beam sampler divides the laser beam into a signal beam and a sample beam. The signal beam is passed through an optical system before being received at the detector while the sample beam is received directly at the detector. The beam sampler is selected such that the received sample beam has a slightly greater steady-state intensity than the received signal beam. The detector circuitry includes two linear wideband photodetectors which produce respective signal and sample currents of opposite polarity. The sample photocurrent is subdivided into two component currents, one of which has substantially the same direct current (DC) value as the signal photocurrent. This component is combined with the signal photocurrent to cancel undesirable noise components in the original laser beam. In a second embodiment of the invention, the dividing circuitry is controlled in a feedback loop to keep the DC portion of the output current at zero.

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