Patent ID: 8867583

Claim:
An excimer laser apparatus comprising: a laser chamber containing a gas; at least a pair of electrodes disposed in said laser chamber; a power source unit including a charger that supplies a voltage between said electrodes; a gas supply unit, connected to one or more receptacles, each of which holds a laser gas and supplies said laser gas to an interior of said laser chamber; a gas exhaust unit that partially exhausts gas from said laser chamber; and a gas control unit that controls said gas supply unit and said gas exhaust unit based on the voltage supplied by said charger, wherein said gas control unit: controls said gas supply unit so as to supply said laser gas to the interior of said laser chamber in a case where the voltage supplied by said charger is greater than a first threshold value; and controls said gas exhaust unit so as to partially exhaust gas from said laser chamber in a case where the voltage supplied by said charger is lower than a second threshold value that is lower than said first threshold value.