Wavelength calibration tool for narrow band excimer lasers

Abstract

An excimer laser system having a precisely calibratable absolute emission wavelength is provided wherein at least one source of reference light is used. The reference light may be a laser such as a HeNe laser or a cathode lamp such as a hollow Pt, As, C, or Fe cathode lamp. The reference light and the excimer laser beam are directed along substantially the same optical path. The beams are broadened and recollimated by beam expanding optics. The broadened beams impinge upon a dispersive element, preferably an echelle grating, and various orders for each incident wavelength are dispersed. The beams are refocused onto a position sensitive detector such as a CCD camera. Different orders of one or more lines of known wavelength of the reference light and a line from the excimer laser emission are also incident at the detector simultaneously. An absolute wavelength calibration of the excimer laser emission is precisely determinable based on a position of said excimer laser emission relative to positions of the one or more lines of the reference light at the detector. The grating constant of the preferred grating and the detector are such that calibration of the central wavelength of the narrowed excimer laser emission is performable when the central wavelength is anywhere within the broadband emission spectrum of the excimer laser. A processor calculates the absolute wavelength of the excimer laser emission. Embodiments are provided for refractive optic, catadioptric, and reflective imaging systems.