Thus, at the start of laser oscillator 1, an anomaly of the gas composition can be discriminated at {TAIL ~ a plurality} of arbitrary low pressures, and {HEAD ~ the reliability} of the discrimination method can be thereby improved 
Thus , at the start of laser oscillator 1 , an anomaly of the gas composition can be discriminated at { TAIL ~ a plurality } of arbitrary low pressures , and { HEAD ~ the reliability } of the discrimination method can be thereby improved
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