Analysis of Second Harmonic Pulse Distortion Induced by Repetitive Irradiation
Shorter pulse duration and higher power lasers have accelerated the development of frequency conversion technique using nonlinear optical crystals for laser precision microfabrications. Previous theoretical studies concerning frequency conversion supposed one-pulse irradiation; accordingly, the influence of the temperature change of crystal induced by laser absorption was not considered, although practical frequency conversions are used with repetitive irradiation. Therefore, researches and developments of harmonic generation with repetitive irradiation have been approached experimentally or empirically. In this study, second harmonic generation considering laser absorption was analyzed theoretically. Output second harmonic pulse shape influenced by repetitive irradiation was evaluated, supposing that the intensity distribution of input pulse was temporal- and spatial-Gaussian. It was quantitatively revealed that a beam profile of output second harmonic pulse, especially generated by high input intensity, is distorted temporally and spatially even during extremely short time-ranges of one pulse. Our analysis suggests the possibility that this pulse distortion influences on processing accuracy.
Yukichi Umakoshi and Shinji Fujimoto
K. Nomura et al., "Analysis of Second Harmonic Pulse Distortion Induced by Repetitive Irradiation", Materials Science Forum, Vol. 512, pp. 343-348, 2006