Research On Surface Topography Extraction And Optical Performance Of Nd:YLF Crystals

Nd:YLF is a new laser crystal material used in solid-state laser.By machining an optical crystal,it leaves a trace on the surface of the optical crystal and does not obtain ideal optical function surface.At present,optical crystal materials are widely processed by a single-point diamond turning method.However,the crystal surface leaves a small-scale ripple and other frequency characteristics which disturb the laser transmission and have an important influence on the optical performance,such as temperature and stress.Therefore the paper studies on frequency characteristics of Nd: YLF surface topography.Actual frequency characteristics of surface topography are being extracted and reconstructed,and the relationship with the processing parameters is been established.Analyzing the effect of actual frequency characteristics on the optical crystal performance is necessary.In the paper original surface topography was obtained by ultra-precision cutting experiment.The white light interferometer measurement showed the surface topography.3-D surface topography and 2-D contour were being extracted and reconstructed by power spectral density method and continuous wavelet transform method.At the same time,the relationship between cutting parameters such as depth of cut,feed rate and spindle speed on actual frequency of surface topography was analyzed.Wavelength and amplitude of frequency characteristic reflected depth of cut and spindle speed,amplitude increased as depth cutting and the spindle speed increasing.Low frequency characteristics reflected feed rate,frequency and amplitude became smaller as the feed rate smaller.High frequency characteristics reflected material properties and vibration during processing.The effects of the ideal scale on the optical performance of the crystal were established,and general rule of contour on temperature and thermal stress was obtained.When wavelength of frequency characteristic was much smaller than incident fundamental wavelength,the beam had no obvious fluctuation inside the crystal and had little effect on temperature and stress.When wavelength of frequency characteristic was same as incident fundamental wavelength,the beam disturbance was obvious,and change of temperature and stress were largest.When wavelength was much larger than fundamental wavelength,amplitude parameter of contour had a greater influence on temperature and stress than wavelength.As amplitude increasing,temperature and thermal stress became larger.Effects of processing parameters on frequency characteristics of crystal surface,and frequency characteristics on crystal optical performance can be obtained.It lays a theoretical foundation for optimizing processing parameters and improving the surface quality.