A novel trapezoid prism homogenizer is used to improve the uniformity of output energy density of excimer laser. The principle and the design requirements of the novel trapezoid prism are analyzed theoretically, and the optimal position of uniform section is calculated. Using this novel homogenizer, the fluctuation of beam uniformity of XeCl excimer laser is less than 4%. The result is better than that obtained from a normal prism homogenizer. The evaluating norms of excimer laser beam uniformity are analyzed in detail. The process window defines uniformity requirements of excimer laser, while the energy fraction answers the problem of useful percentage of energy within a giving process window. The top-hat factor defines the uniformity in the whole energy range, and the dynamic range is the variation range of screen-homogenizer in the specific application. Using this evaluating norm the uniform beam obtained by the novel trapezoid prism homogenizer is analyzed.
In this study, high efficient backward Raman compression has been achieved by a 10J KrF pump laser from Heaven-1 MOPA system using focused-beam geometry. A preliminary stage of experiments was carried out in CIAE with main results reported here. Up to 1.7J of first backward Stokes(268nm) output with pulse duration of 1.5ns was obtained as the pump (248nm) laser was 1OJ of energy and 22ns of pulse duration. The pulse duration is compressed by 15 times with total energy conversion efficiency up to 17%. The high conversion efficiency of backward SRS is considered mainly attributing to the focused geometry. The mechanisms of backward Stokes pulse self-shortening and forward-backward gain asymmetry compensating have been discussed. The backward Stokes pulse duration is considered to be much less than it was observed using a relatively lower bandwidth oscillograph. Further experimental research on precision time measurement will be performed later this year.
A relative good and economical method has been presented to fabricate V-grooves on LiNbO<SUB>3</SUB> crystal for passive fiber alignment. It ha been experimentally investigated of excimer laser ablated V-grooves on LiNbO<SUB>3</SUB> crystal. Two excimer lasers were employed for comparison experiment with the wavelength of 308nm and 193nm respectively. It has been shown that 308nm wavelength performed a poor role in fabricating grooves on LiNbO<SUB>3</SUB> crystal, particularly on both ablation sped and surface quality, while 193nm wavelength showed excellent performance. The corresponding ablation threshold of LiNbO<SUB>3</SUB> crysatl at 193nm has been found to be as low as 0.5J/cm<SUP>2</SUP>. At laser fluence of 3J/cm<SUP>2</SUP> and 1200 shots of laser irradiation, V-grooves with some 130 micrometers have been fabricated without visible damage near the grooves. Oxygen buffering atmosphere has been utilized for improving ablation surface cleansing.