Dynamics of Output Spectra within a Single Laser Pulse from a Line-Narrowed Excimer Laser

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Abstract
We describe the dynamic behavior of spectral line-narrowing during a single laser pulse generated from a line-narrowed KrF excimer laser used in optical lithography. To study the details of the dynamics, a spectral monitoring system, composed of a Fabry-Perot interferometer, a streak camera, and a numerical simulation code was developed. In the laser studied, the spectral bandwidth of 1.5 pm in full width at half maximum (FWHM) at the beginning of the pulse was narrowed to 0.8 pm (FWHM) with the wavelength selective elements having a passive transmission bandwidth of about 2.9 pm (FWHM). The results of the numerical calculations were in reasonable agreement with the experimental results, and showed that the time-integrated line-width in the present laser system was narrowed only to 40% of the transmission bandwidth of the spectral selective elements in the cavity.