Proceedings PaperOvercoming limitations of etalon spectrometers used for spectral metrology of DUV excimer light sources
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Etalon spectrometers often provide the practical means for providing pulse-resolved spectral metrology of line-narrowed excimer laser lithographic light sources because of their relative simplicity and physical robustness. A typical application uses the full-width at half-maximum intensity (FWHM) of an etalon fringe to infer the FWHM bandwidth of an unknown input spectrum. These devices are often used in a regime where the ratio of the width of the spectrometer impulse-response to the bandwidth of the source spectrum is close to (or greater than) unity. In this regime, the fringe width may have non-negligible sensitivity to details of the source spectral shape other than its FWHM, including asymmetry and spectral purity. This paper details this sensitivity and provides suggestions for techniques that can either suppress the effect or apply it to some advantage such as estimation of a spectral purity metric, e.g., the 95%-enclosed energy width (E95%) of the source spectrum.