Photomultiplier output-gating circuit

  
The application involves observing the light pulse emerging from a thick specimen after transillumination by a laser pulse. Pulses derived from the laser source are amplified using a Video Amplifier LM733. The reference level is set to 1 V in the comparator LM 710, to provide the necessary trigger pulses for the monostable multivibrator 74121. The laser pulses have a repetition frequency of 500 Hz and suitable values are as below: Rl = 33 k ohm, Cl = 22 pF R2 = 33 k ohm, C2 = 68 nF.
Photomultiplier output-gating circuit  - schematic

The pulse width for each monostable is approximately given by tw = 0.7 RC. R3 and C3 is a high pass filter. The method therefore permits the use of low cost components having moderate response times for extracting the pulse of interest.




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