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