Numerical analysis of harmonic generation process in a high-repetition-rate all-solid-state 213nm laser

Abstract

We reported 0.4W average power all-solid-state 213nm laser, which is a potential candidate for next generation micro-lithography1,2. For this application, the power should be scaled up to more than 5W to be competitive with an excimer laser. To investigate such scalabilty, we analyzed numerically SHG and FHG processes with an intensive tightly focused Gaussian pump beam from Lightwave Electronics model-210 diode-pumped Q-switched Nd:YAG laser of which average power is more than 6W with 35ns pulse width in FWHM at 7 kHz repetition rate. Our apporoch is based on Boyd and Kleinman’s method which is effective to analyze harmonic generation process in a nonlinear crystal with a tightly focused Gaussian pump beam3. However, calculation of pump depletion was only allowed in plane wave approximation4,5. To include the effect of pump depletion into the conversion process, we formulated harmonic power increment at an arbitrary point along the propagation direction (z-direction) of the pump beam in a nonlinear crystal. From energy conservation law, the harmonic increment should be related to pump depletion. Under assumption of homogeneous Gaussian beam depletion, fundamental and harmonic intensity at 800 points along the propagation direction of a fundamental beam in nonlinear crystals were calculated by integrating the fundamental decrement and the harmonic increment on a workstation Sony NWS-5000 in a couple of seconds.