Effect of Actual Frequency Features Generated in Machining Process on the Temperature and Thermal Stress of Potassium Dihydrogen Phosphate Crystal

Abstract Temperature and thermal stress can affect the laser-induced damage threshold of Potassium Dihydrogen Phosphate (KDP) crystals. In this work, actual frequency features in the machined surface of KDP crystal are extracted and reconstructed by power spectral density and continuous wavelet transform methods. Wave optics theory is used to calculate the effect of surface frequencies on the temperature and thermal stress of KDP crystals exposed to laser irradiation at a wavelength of 1.064μm and the power of 200 MW/μm2 in 1 ns. According to the results, the temperature and thermal stress increase once the wavelength of surface frequency approaches the incident laser wavelength. With a further increase in the wavelength (1.064-20μm), maximum temperature and thermal stress exhibit a tendency to decline. When the wavelength of surface frequency exceeds 60μm, maximum temperature and thermal stress keep constant with changing surface frequency. Maxium temperature and thermal stress are found to be proportional to the amplitudes of frequency features at the same wavelength. Furthermore, temperature affected by actual frequency is 4-12 K higher than that in the case of ideal frequency at the same wavelengths and amplitudes. With increasing wavelength, the positions of maximum temperature and thermal stress extend to the interior of KDP crystal.