Characteristics of Local Modulation Beam Propagating through Spatial Filter System

Kewei You,Yanli Zhang,Jianqiang Zhu,Xuejie Zhang

doi:10.1155/2018/2545923

Abstract

As local defects may significantly harm beam quality and affect safe operation, a systematic analysis of the ability of a spatial filter to alleviate these adverse effects is required. Thus, the evolutional characteristics of a beam modulated by a local defect propagating through a spatial filter system at an image reply plane and a downstream plane are analyzed in detail. Modulation stripes appear at the image reply plane; these are caused by the pinhole cutoff effect. The modulation degree increases with increasing defect size. The maximum intensification factor can reach 3.2 under certain conditions. Thus, the defect size should be restricted to a reasonable size for safe operation with a specified pinhole size. Moreover, a maximal value appears at the downstream plane, and the intensity enhances with increasing defect size. To ensure beam quality, the maximum allowable defect size and angle of the spatial filter should meet special constraints. The maximum allowable defect size is calculated based on practical configuration parameters.

Highlights

In a high-power laser system, the laser beam passes through numerous optical components
The amplitude and phase modulations caused by damage defects and contamination particles can result in downstream intensification, which can damage certain optical components in the systems [1,2,3,4,5]
It is well known that local diffraction modulation may cause a great threat to expensive downstream optical components, so much attention should be paid to how the modulated beam is suppressed by transmitting a spatial filter

Summary

Introduction

In a high-power laser system, the laser beam passes through numerous optical components. As one of the crucial factors restricting the output power of high-power laser systems, the research of defects in optical components has aroused great interest for a long time. There are still some researches about controlling features of spatial filter on nonlinear growth with small soft Gaussian scatterers perturbation [13], but little work is done about local circular defects which is commonly found from the near-field measurement in practical systems. It is well known that local diffraction modulation may cause a great threat to expensive downstream optical components, so much attention should be paid to how the modulated beam is suppressed by transmitting a spatial filter. Based on this analysis, some specific cleanliness rules about amplifier and optical components are put forward, thereby providing useful guidance for the inspection of optical components

Theoretical Model

Numerical Simulations and Result Analysis

Findings

Conclusion