{TAIL ~ The signal} m of usually about 1 mW is actually changed to {HEAD ~ a level} of about 2 mW. Thus, the signal m from the irradiation beam photo detector 10 changes 
{ TAIL ~ The signal } m of usually about 1 mW is actually changed to { HEAD ~ a level } of about 2 mW. Thus , the signal m from the irradiation beam photo detector 10 changes
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH