Line-narrowed KrF excimer laser apparatus

A line-narrowed KrF excimer laser apparatus comprising:

• a laser chamber including a first window and a second window, the laser chamber accommodating a pair of discharge electrodes and configured to seal a laser gas including krypton gas and fluorine gas;
• a line narrow optical system provided in an optical path of light emitted from the first window;
• an actuator capable of changing a wavelength of light selected by the line narrow optical system;
• an output coupling mirror constituting an optical resonator with the line narrow optical system, the output coupling mirror being provided in an optical path of light emitted from the second window and configured to emit a part of the light emitted from the second window;
• a wavelength detecting unit including
• a low-pressure mercury lamp accommodating mercury, a getter material that adsorbs at least a part of the mercury, and a hot cathode that excites at least a part of the mercury,
• an etalon provided at a position where reference light emitted from the low-pressure mercury lamp and detected light emitted from the output coupling mirror are incident on the etalon, and
• a light intensity distribution sensor configured to detect an intensity distribution profile of interference fringes of the detected light and an integrated profile obtained by integrating an intensity distribution profile of interference fringes of the reference light for a predetermined period from time at which the low-pressure mercury lamp starts emitting the reference light;
• and
• a wavelength controller configured to perform
• calculating a wavelength of the detected light based on the integrated profile and the intensity distribution profile of the interference fringes of the detected light, and
• controlling the actuator based on results of calculation of the wavelength of the detected light.