Patent ID: 10615565

Abstract:
The line narrowed laser apparatus configured to perform a plurality of burst oscillations including a first burst oscillation and a second burst oscillation next to the first burst oscillation to output a pulse laser beam. The line narrowed laser apparatus comprises a laser resonator, a chamber provided in the laser resonator, a pair of electrodes provided in the chamber, an electric power source configured to apply pulsed voltage to the pair of electrodes, a wavelength selecting element provided in the laser resonator, a spectral width varying unit provided in the laser resonator, and a controller. The controller is configured to measure a duty in a predetermined period before starting the second burst oscillation and a length of a suspension period from a time of ending the first burst oscillation to a time of starting the second burst oscillation, and perform a first control of the spectral width varying unit based on the duty and the length of the suspension period.