Gas laser apparatus

A gas laser apparatus comprising:

• a first 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 second laser chamber connected through a sixth control valve to the first laser gas supply source and connected through a seventh control valve to the second laser gas supply source;
• a common pipe connected to the second laser gas supply source and divided into a first branch pipe in which the second control valve is disposed and a second branch pipe in which the seventh control valve is disposed;
• a fourth control valve disposed in the common pipe;
• 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 first laser chamber and at least a part of a gas exhausted from the second laser chamber;
• and
• a booster pump, connected through a third control valve to the common pipe between the fourth control valve and a place where the common pipe is divided into the first and second branch pipes, the booster pump being configured to raise 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 first laser chamber and an operating gas pressure of the second laser chamber.