Wavelength and pulselength dependence of laser conditioning and bulk damage in doubler-cut KH2PO4

An experimental technique has been utilized to measure the variation of bulk damage scatter with damaging fluence in plates of KH2PO4 (KDP) crystals. Bulk damage in unconditioned and laser-conditioned doubler-cut KDP crystals has been studied using 527 nm (2w) light at pulselengths of 0.3 - 10 ns. It is found that there is less scatter due to damage at fixed fluence for longer pulselengths. In particular, there is similar to 4X increase in fluence for equivalent scatter for damage at 2w, 10 ns as compared to 0.30 ns in unconditioned KDP. The results for the unconditioned and conditioned KDP show that for all the pulselengths the scatter due to the bulk damage is a strong function of the damaging fluence (phi(similar to 5)). It is determined that the 2w fluence pulselength-scaling for equivalent bulk damage scatter in unconditioned KDP varies as tau(0.30 +/- 0.11) and in 3w, 3ns ramp-conditioned KDP varies as tau(0.27 +/- 0.14). The effectiveness of 2w and 3w laser conditioning at pulselengths in the range of 0.30-23 ns for damage induced 2w, 3 ns is analyzed in terms of scatter. For the protocols tested (i.e. peak conditioning irradiance, etc.), the 3w, 300 ps conditioning to a peak fluence of 3 J/cm(2) had the best performance under 2w, 3 ns testing. The general trend in the performance of the conditioning protocols was shorter wavelength and shorter pulselength appear to produce better conditioning for testing at 2w, 3 ns.