Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH2PO4 crystal

doi:10.1088/1674-1056/23/8/087702

Abstract KH₂PO₄ (KDP) crystal with excellent optical properties is a very important element of inertial confinement fusion (ICF) device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage threshold, affecting the crystal service life. In this paper, Gaussian repaired pit is used to replace the crystal surface micro-defects, in order to improve the laser damage resistance of the KDP crystal with surface micro-defects. At first, the physical model of Gaussian repaired pit is built by Fourier model method, and the accuracy of the method is analyzed. It is found that the calculation error can be reduced by increasing the product of the width-period ratio and the truncation constant of the repaired pit. The calculation results about the physical model of Gaussian repaired pit show that the light intensity distribution within the crystal is symmetrical, and there are evidently enhanced light intensity regions in the crystal. Meanwhile, the maximum relative intensity inside the KDP crystal decreases gradually with the increase of the width of the Gaussian repaired pit. Secondly, the Gaussian repaired pits with different widths and the same depth of 20 μm are processed by micro-milling. Their surfaces are very smooth and present the ductile cutting state under the microscope. Finally, the laser damage threshold of the Gaussian repaired pits on the surface of the KDP crystal sample is measured by a 3ω, 6-ns laser. The results show that the maximum threshold of the Gaussian repaired pits is 3.12 J/cm², which is 60% higher than the threshold of initial damage point, and the laser damage threshold increases with the increase of the width of the Gaussian repaired pit.

Keywords: KH₂PO₄ Gaussian repaired pit Fourier modal method laser damage threshold

Received: 23 October 2013
Revised: 20 February 2014
Accepted manuscript online:

PACS:	77.84.Fa	(KDP- and TGS-type crystals)
	42.60.Jf	(Beam characteristics: profile, intensity, and power; spatial pattern formation)
	02.30.Nw	(Fourier analysis)
	42.70.Mp	(Nonlinear optical crystals)

Fund: Project support by the National Natural Science Foundation of China (Grant No. 51275113) and the National Science and Technology Major Project of China (Grant No. 2013ZX04006011-215).

Corresponding Authors: Chen Ming-Jun
E-mail: chenmj@hit.edu.cn

Cite this article:

Xiao Yong (肖勇), Chen Ming-Jun (陈明君), Cheng Jian (程健), Liao Wei (廖威), Wang Hai-Jun (王海军), Li Ming-Quan (李明全) Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH₂PO₄ crystal 2014 Chin. Phys. B 23 087702

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Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH2PO4 crystal

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Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH₂PO₄ crystal