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