Gas laser apparatus

A gas laser apparatus comprising:

• a laser chamber connected through a first control valve to a first laser gas supply source that supplies a first laser gas containing a halogen gas and connected through a second control valve to a second laser gas supply source that supplies a second laser gas having a lower halogen gas concentration than the first laser gas;
• a purification column that removes at least a part of the halogen gas and a halogen compound from at least a part of a gas exhausted from the laser chamber;
• a booster pump, connected through a third control valve to the laser chamber, which raises a pressure of a gas having passed through the purification column to a gas pressure that is higher than an operating gas pressure of the laser chamber;
• a first tank disposed between the purification column and the booster pump;
• a first pressure sensor that measures a first pressure inside the first tank;
• a second tank disposed between the booster pump and the third control valve;
• a second pressure sensor that measures a second pressure inside the second tank;
• and
• a controller that controls the booster pump on a basis of the first pressure and controls the third control valve on a basis of the second pressure, wherein
• the controller controls the booster pump so that the first pressure inside the first tank falls within a range from an atmospheric pressure to 1300 hPa when the third control valve is closed,
• the booster pump sends gas to the second tank such that the second pressure inside the second tank is equal to or higher than a pressure in a pipe connecting the second control valve and the second laser gas supply source, and
• the controller controls the third control valve to be open such that the gas in the second tank is supplied to the laser chamber when the second pressure inside the second tank is equal to or higher than the pressure in the pipe.