The low frequency and d.c. components of the photo detector output are proportional to the average light intensity incident thereon, and {HEAD ~ an error signal} derived from {TAIL ~ the comparison} thereof with a reference voltage is compensated, amplified, and limited, and applied to a regulator to control the discharge current of a laser light source 
derived from
The low frequency and d.c . components of the photo detector output are proportional to the average light intensity incident thereon , and { HEAD ~ an error signal } derived from { TAIL ~ the comparison } thereof with a reference voltage is compensated , amplified , and limited , and applied to a regulator to control the discharge current of a laser light source
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