Effect of 3D surface topographies on the temperature field of machined potassium dihydrogen phosphate crystals

3D actual frequencies in the machined Potassium dihydrogen phosphate (KH2PO4, KDP) crystal surfaces are extracted and reconstructed through continuous wavelet transform (CWT) and power spectral density (PSD) methods. The temperatures of machined KDP crystals, which are exposed to laser irradiation with a wavelength of 1.064 μm and power of 200 MW/μm² in 1 ns, are analyzed with wave optics. The ideal surfaces have been selected to analyze the impact of wavelength and amplitude on the internal temperature field of KDP crystals. Along the orthogonal direction of cutting, the closer the dominant 3D wavelength of the surface is to the laser's incident wavelength, the greater the temperature increase. The maximum temperature decreases with the further increase of the wavelength (1.064-20 μm). The effect of the frequency feature on temperature in the cutting direction is similar to that in the orthogonal direction, but with a lesser impact on temperature variation. The temperatures of 3D surfaces and sub-surfaces above 10 μm depth are calculated using the wave optics theory. The maximum temperature field throughout the crystal is in the subsurface layer. With the increase of wavelength, the positions of the maximum temperature extend to the interior of the KDP crystal.