Patent ID: 7203217

Claim:
A narrow band electric discharge gas laser with minimized wavelength variations caused by fluctuations in laser gas density resulting in laser beam directional changes comprising: A) a laser chamber, B) an elongated electrode structure enclosed within said chamber comprising an elongated anode and an elongated cathode separated by a distance defining a discharge region in which a discharge laser beam is amplified, said discharge region defining a long dimension in a beam direction, C) a laser gas contained in said chamber, D) a fan for circulating said laser gas within said chamber and through said discharge region, E) an output coupler, F) a grating based line narrowing module comprising a grating and a tuning means to control direction of illumination of light from said chamber on said grating, said direction of illumination defining an illumination direction, (G) a test laser producing a test laser beam directed along a path through said discharge region and into said line narrowing module and reflecting at least once off said grating, H) a fast beam deflection monitoring means to monitor deflection of said test laser beam; and I) a feedback control means for controlling said tuning means based on signals from said beam deflection monitoring means.