CHAPTER 5 LASER EXPOSURE SYSTEM
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B. Stabilizing the Laser Output
The laser output tends to vary appreciably in response to changes in the ambient temperature.
The machine controls the mechanism so as to ensure stable output:
The laser beam is emitted.
The laser beam is detected by the photodiode (PD) built in the laser element.
The output voltage (sample voltage) of the photodiode is returned to the APC circuit.
The sample voltage is compared against the target voltage to determine the laser drive current.
The laser beam is monitored (for every line scan), and the drive current is varied on a real time
basis to ensure a stable laser beam.