Since the laser power detection circuit 11 often has an abnormal emission slice level n1 of about 1.5 mW set relative to the signal m of about 1 mW, the detector 11 detects this interval as the abnormal emission, thus producing the output signal p of {TAIL ~ H1 voltage} by which {HEAD ~ the laser drive circuit} 21 is controlled to stop the beam emission of the laser beam source 1 
Since the laser power detection circuit 11 often has an abnormal emission slice level n1 of about 1.5 mW set relative to the signal m of about 1 mW , the detector 11 detects this interval as the abnormal emission , thus producing the output signal p of { TAIL ~ H1 voltage } by which { HEAD ~ the laser drive circuit } 21 is controlled to stop the beam emission of the laser beam source 1
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