Laser apparatus including gas supply device and exhausting device

A laser apparatus comprising:

• a chamber in which a pair of discharge electrodes is provided;
• a gas supply device configured to supply first laser gas including halogen gas and second laser gas having a halogen gas concentration lower than the first laser gas to the chamber;
• an exhausting device configured to exhaust laser gas in the chamber;
• a pressure sensor configured to measure gas pressure in the chamber;
• a controller configured to select one of a first gas control and a second gas control based on the gas pressure measured by the pressure sensor,
• the first gas control causing the first laser gas to be supplied to the chamber such that the gas pressure in the chamber after the first gas control is higher than the gas pressure in the chamber before the first gas control,
• the second gas control causing at least one of the first laser gas and the second laser gas to be supplied to the chamber and causing a part of the laser gas in the chamber to be exhausted such that a difference between the gas pressure in the chamber before the second gas control and the gas pressure in the chamber after the second gas control is smaller than a difference between the gas pressure in the chamber before the first gas control and the gas pressure in the chamber after the first gas control, and
• any one of the first gas control and the second gas control is executed in a period of performing laser oscillation, wherein
• the controller compares the gas pressure measured by the pressure sensor and a predetermined threshold value,
• the controller selects the first gas control when the gas pressure measured by the pressure sensor is lower than the predetermined threshold value,
• the controller selects the second gas control when the gas pressure measured by the pressure sensor is higher than the predetermined threshold value, and
• the controller is a gas controller;
• and
• a laser controller which performs adjusting oscillation at every time a total gas replacement of the chamber is executed,
• wherein the gas controller sets the predetermined threshold value based on the gas pressure in the chamber after the adjusting oscillation is performed.