An excimer laser cavity is disclosed which includes at least one grating-prism (grism) and a wavelength-selective diffraction grating arranged in sequence. The grism grating surface faces the gain medium and produces an expanded beam which is diffracted on the same side of the prism grating surface normal as the incident beam. The expanded diffracted beam is transmitted through a second surface of the grism either to another grating surface of an additional grism or to a wavelength-selective diffraction grating operating in Littrow configuration. The laser produces a laser output beam with a narrow spectral linewidth which is suitable, in particular, for lithography applications.