Patent ID: 7751461

Claim:
A line-narrowed excimer laser system comprising: a laser cavity comprising a gain medium, an output coupler and a reflector assembly, the reflector assembly comprising at least two sequentially arranged grating-prisms (grisms), each grism having an input surface and an output surface, and a wavelength-selective diffraction grating arranged in sequence, with a first of the at least two grisms having a first grating disposed on the input surface of the first grism and facing the gain medium, with the first grating operating in 2 nd order and receiving laser light from the gain medium at a first angle of incidence with respect to a first grating normal, wherein the first angle of incidence is selected so as to produce a first diffracted expanded beam which is diffracted on the same side as the incident beam in relation to the first grating normal, with the first expanded diffracted beam exiting the output surface of the first grism and impinging on a second grating disposed on the input surface of the second of the at least two grisms at a second angle of incidence with respect to a second grating normal, wherein the second angle of incidence is selected so as to produce a second expanded diffracted beam which is diffracted on the same side as the first expanded diffracted beam in relation to the second grating normal, with the second expanded diffracted beam transmitted through the output surface of the second grism to the wavelength-selective diffraction grating, wherein the wavelength-selective diffraction grating operates in Littrow configuration and diffracts the received expanded diffracted beam back through the at least two grisms into the laser cavity, thereby narrowing the linewidth of the laser emission wavelength relative to the wavelength distribution of the laser light produced in the gain medium.