Method and device for spectral measurements of laser beam

Abstract

A fast response etalon based spectrometer for spectral measurement of a pulse laser beam. A portion of the beam is directed through a double pass etalon device which provides angular separation of spectral components of the beam. The spectral components are measured by a fast photodiode array. In a preferred embodiment periodic photodiode data is also collected between pulses to record background dark current values for each photodiode in the array. In a preferred embodiment at least one set of dark current data is collected for each set of laser spectral data embodiments and the dark current data are subtracted from the laser spectral data to provide corrected spectral data at rates of up to 2000 Hz or greater. The spectrometer is very compact producing precise fringe data permitting bandwidth measurements with precision needed for microlithography for both ΔλFWHM and Δλ95%.

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