Wavelength system for an excimer laser

A wavelength system for measuring and controlling wavelength of a laser beam produced by a narrowband laser, said system comprising:

• A. a wavemeter for measuring incremental changes in wavelength;
• B. an atomic wavelength reference for calibrating said wavemeter, said reference comprising:
• 1) a vapor cell for containing a vapor having an absorption line near a desired operating wavelength for said laser;
• and
• 2) a calibration light detector for measuring intensity of light passing through said vapor cell;
• C. a tuning device having a tuning range sufficient to tune said laser to a range of wavelength encompassing said absorption line;
• D. an optical train arranged to simultaneously direct portions of said narrow band laser beam (i) to said wavemeter;
• and (ii) through said vapor cell to said calibration light detector;
• and
• E. a processor for collecting and analyzing data from said calibration light detector and said wavemeter over said range of wavelengths and, based on such analysis, calibrate said wavemeter.