Patent ID: 8576891

Claim:
A gas laser oscillator that is a sealed gas laser oscillator including an airtight vessel, a laser gas supply source that supplies a laser gas to the airtight vessel, and a vacuum pump that is connected to the airtight vessel and performs evacuation until a pressure of an inside of the airtight vessel reaches a target reached pressure every predetermined interval between laser gas exchanges and, and that performs laser oscillation in a state where the airtight vessel is filled with the laser gas, the gas laser oscillator comprising: a unit that determines the target reached pressure such that the target reached pressure becomes equal to or less than a value obtained by subtracting a product of an interval between laser gas exchanges and a leakage rate of an impurity gas into the airtight vessel from an outside after evacuation from an allowable impurity gas pressure at which the gas laser oscillator is capable of being operated.