means for regulating the intensity of the source of laser light in {HEAD ~ response} to {TAIL ~ the error signal}, to thereby maintain the light intensity on the photo detector substantially constant, 
means for regulating the intensity of the source of laser light in { HEAD ~ response } to { TAIL ~ the error signal } , to thereby maintain the light intensity on the photo detector substantially constant ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH