wherein said {HEAD ~ defect detection circuit} continues to maintain said {TAIL ~ substantially constant output voltage} to said drive circuit when said amount of irradiation beam detection signal exceeds said reference voltage for a period of time that is less than a predetermined period of time 
continues to maintain
wherein said { HEAD ~ defect detection circuit } continues to maintain said { TAIL ~ substantially constant output voltage } to said drive circuit when said amount of irradiation beam detection signal exceeds said reference voltage for a period of time that is less than a predetermined period of time
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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