Since {HEAD ~ 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 {TAIL ~ this interval} as the abnormal emission, thus producing the output signal p of H1 voltage by which the laser drive circuit 21 is controlled to stop the beam emission of the laser beam source 1 
Since { HEAD ~ 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 { TAIL ~ this interval } as the abnormal emission , thus producing the output signal p of H1 voltage by which the laser drive circuit 21 is controlled to stop the beam emission of the laser beam source 1
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