In this study, silicon carbide ceramic (SiC) was processed by a high repetition frequency femtosecond laser with a wavelength of 1030 nm. We have analyzed the affection of different parameters to the material removal rate and researched surface oxidation phenomenon during laser scanning. The surface oxidation phenomenon is a major factor that affects the material removal rate of SiC ceramic and may even lead to failure of material removal. The oxidation phenomenon of the processing area is directly related to the laser induced temperature rise. Increasing laser scanning speed and increasing laser scanning interval are effective methods to reduce the oxidation phenomenon. The experiments have demonstrated that high-speed processing of SiC ceramic by high repetition frequency femtosecond laser is available under certain parameters.
Publisher’s Note: This paper, originally published on 8 July 2019, was replaced with a corrected/revised version on 13 August 2019. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
When Potassium Dihydrogen Phosphate (KDP) crystal is irradiated by nanosecond laser with fluences exceeding its damage threshold, laser-induced damage occurs in the bulk or on the surfaces of crystal components. Such damage process is a multi-physical coupling process which is composed of energy deposition stage, temperature/pressure rising stage and subsequent micro explosion stage. So far, great efforts have been made in modeling the energy deposition and temperature/pressure rising stages of the damage process, but little attention has been paid on the subsequent micro explosion event. As a result, it is still impossible to reproduce the laser damage phenomena such as damage crater formation and shockwave propagation with the existing damage models. To address this concern, equivalent explosion simulation model for studying the laser-induced damage process of KDP crystals has been constructed by finite element method (FEM). According to the model, explosion energy leading to damage, formation of damage craters and propagation of shockwave can be obtained. Moreover, laser damage experiments combined with time-resolved techniques have been utilized to investigate the impact of laser fluences on the shockwave speed. Experiment results agree well with the simulated phenomenon, which has proved the validity of the simulation model.
The application of fused silica in the field of High power laser requires that the formation of sub-surface damage be reduced in the process of grinding and polishing. Subsurface damage is unavoidable in traditional processing methods. Laser smoothing, as a non-contact polishing method, has attracted more and more attention in the surface treatment of fused silica. Laser smoothing is capable of producing smooth surface without incurring serious mechanical defects. Thus it is employed to polish fused silica in the hope of reducing mechanical defects on the optical components. In this paper, aiming at the ground surface of fused silica, the characteristics of mid-far infrared laser treatment and modification are studied. The surface smoothness under different laser power are studied, and the optimal laser power and action time for laser smoothing are obtained. This technology can reduce the ground surface roughness from above 100 nanometer to nanometer.
To improve the surface quality and laser damage resistance of Potassium Dihydrogen Phosphate (KDP) crystal processed by single point diamond fly-cutting (SPDF) technique, formation and suppression of KDP surface defects are investigated. Firstly, multiple measuring methods have been utilized to characterize KDP surface defects. According to their structure and chemical characters, KDP surface defects were classified into four categories and forming reason of each was analyzed. Based on these analysis results, theoretical model for describing the formation process of KDP surface defects was established and conditions for achieving defects-free KDP surfaces were proposed. Finally, flycutting experiments were carried out to verify the effect of the defects suppression measures. Experiment results indicate that smooth KDP surface with roughness less than 2 nm can be obtained and KDP surface defects can be suppressed effectively by applying the proposed methods.
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