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Effect of nonideal wavefront on the near filed beam quality disturbed by flaw in target system

In high-power laser facilities for inertial confinement fusion, there are many large-diameter optical elements, which inevitably have some flaws on the surface. The beam is modulated by these flaws after diffraction transmission, thereby reducing the beam quality of the system. The optical field with high modulation may cause self-focusing in fused silica and thus damage the optical components, which seriously affects the load capacity of the device. Therefore, for high-power laser systems, near field beam quality also has a high demand. In this paper, the effect of flaws and nonideal wavefront of sinusoidal modulation on the near-field quality at specific position behind the focusing lens is analyzed for final target system of high power laser device based on the Huygens-Fresnel diffraction theory. Firstly the beam modulation of ideal wavefront disturbed by flaws is investigated. And the modulation by phase type flaw is more serious than amplitude type. Secondly, near field beam modulation of nonideal wavefront of sinusoidal phase disturbed by flaws is analyzed. Results demonstrate that under some specific conditions of sinusoidal phase, modulation degree is reduced and the beam quality is improved by the nonideal wavefront compared to the ideal wavefront. The results could give some references to the improvement of near field beam quality and mitigation of risk of optical damage caused by self-focusing.