<title>High-average-power narrow-band KrF excimer laser</title>

Abstract

The conventional line-narrowing methods employed by narrow band KrF excimer lasers are intra-cavity etalons method and a Littrow grating with beam expansion method. They have the following problems in high average power operation; a)short lifetime of the etalons and large wavelength drift and large line-width change(the etalons method) or b)low output power and short lifetime of electrodes(the grating method).To solve the above problems, we propose a hybrid method consisting of two prism beam expanders, an etalon and a Littrow grating. These prism beam expanders decrease the light intensity on the etalon, so that the lifetime of the etalon is increased drastically, the passive wavelength drift is minimized, and the wavelength is adjusted quickly. By employing this system, we got average power of more than 8 W, line-width of less than 2.5 pm(FWHM) and long term wavelength stability of less than pm.