Influence of period and amplitude of microwaviness on KH₂ PO₄ crystal's laser damage threshold

The laser induced damage threshold (LIDT) has become a technical bottleneck which restricts the application and development of the inertial confinement fusion. Using single point diamond turning method to process KH₂ PO₄ (KDP) crystals, the periodic microwaviness will be left on the machined surface which has a significant impact on the LIDT. In this paper, after acquiring the frequency information of machined surface of KDP crystals with the power spectral density method, we analyze quantitatively the influence of microwaviness on the LIDT of KDP crystal with the Fourier modal theory. Research results indicate that: the surface morphology of KDP crystal is consisted of the subwaviness with different characteristic spatial frequencies; and the reduced amount of the LIDT of KDP crystal leaded by such subwaviness is different; the experimental results of the LIDT are consistent with the theoretical calculations basically; for the machine tool and the processing technology we used, the leading frequency of microwaviness which caused the LIDT decreasing is between (350 μm)^-1 and (30 μm)^-1, especially between (90 μm) -1 and (180 μm) -1.