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Influence of Micro-Nano Superficial Micro-Waveness on KDP Crystal’s Laser Damage Threshold

Author: JiangWei
Tutor: ChenMingJun
School: Harbin Institute of Technology
Course: Mechanical Manufacturing and Automation
Keywords: KDP crystal micro-waveness laser damage threshold Fourier modal method power spectral density
CLC: TN241
Type: Master's thesis
Year: 2009
Downloads: 92
Quote: 1
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Abstract


KDP crystal is mainly used in the Inertial Confinement Fusion (ICF) terminal optical system for frequency multiplication and Pockels cells. However, the laser induced damage threshold (LIDT) of KDP crystal is very low, and restricts the ultra high-power solid-state laser driver to drive the nuclear target, what has become a bottleneck that restricts the application and development of ICF. Recently, the studies on the LIDT are focused on the factors like stationary-state and transient-state deficiency inside the crystals, impurity content, multi-photon ionization and collision ionization inside the crystals, etc. Actually the micro-waveness on the machined surface of KDP crystal has an important impact on the distribution of electromagnetic field energy density and the damage threshold. Therefore, making an in-depth study on the laser damage mechanism affected by micro-waveness and the evaluation method not only can provide the theoretical basis for increasing LIDT, but also can guide effective working parameters choosing and processing technology improving.In this paper the electromagnetic field of the stratified areas in the micro-waveness model is solved by Fourier modal method, which is based on the rigorous electromagnetic theory; the mechanism and the law of how the micro-waveness impacting on the laser damage threshold is analyzed theoretically for KDP crystal; combined with the power spectral density (PSD) method which is based on the Fourier spectrum analysis, the evaluation method of how the machined surface (composed by micro-waveness of different spatial frequencies) impacting on the laser damage threshold is given for KDP crystal.Variable parameter processing experiments of KDP crystal is carried out using single point diamond turning (SPDT) method, and the three-dimensional morphology of the machined surface is detected by atomic force microscope (AFM) and white light interferometer, respectively; the surface data is analyzed by PSD method, and combined with the evaluation method of this paper the theoretical result of laser damage threshold in different processing parameter areas of KDP crystal is obtained; the experiment of laser damage threshold detection by 1-on-1 method and the transmittance detection experiment are completed, and the experimental results are analyzed compared with the theoretical results, which verifies the feasibility of the theoretical model and the evaluation method.The evaluation results of the machined surface are analyzed statistically, and the range of the spatial frequency is obtained, in which the micro-waveness compositions of the machined surface lead to the decreasing of the laser damage threshold of KDP crystal. Using the statistical results, the shortages in the processing technology can be found and improved to increase the laser damage threshold of KDP crystal.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Laser physics and basic theory
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