大口径KDP晶体紫外光横向受激拉曼散射风险判据研究

Risk Evaluation of Transverse Stimulated Raman Scattering in Large-Aperture,High Fluence KDP Crystal

研究了高功率固体激光驱动器运行于高通量、长脉冲条件下,大口径三倍频KDP晶体中强紫外光激发的横向受激拉曼散射(TSRS)效应,重点分析了受激拉曼散射(SRS)过程产生的散射光场峰值功率密度、峰值通量与抽运脉冲脉宽、晶体侧边反射率的关系。将晶体侧边反射折算为散射光传输过程的固有损耗,理论研究结果表明任意抽运脉宽、任意晶体侧边反射率条件下散射光峰值光强总满足e指数增长规律,并推导了增长系数G的一般表达式。此外,在任意拉曼增益系数、任意抽运脉宽与晶体边缘反射率条件下,一旦增长系数G高于25,散射光峰值通量将达到约10 J/cm2,逼近晶体损伤通量,由此给出KDP晶体紫外光横向受激拉曼散射风险判据。

The effect of transverse stimulated Raman scattering （TSRS） in large-aperture KDP frequency-conversion crystals in high-power solid laser drivers operating at long pulse duration and higher energy fluence is studied. The relationship between maximum of the intensity and fluence of Stokes field produced during Raman scattering, and pulse widths of pump laser as well as crystal edge reflectivity have been presented. The result shows that the maximum intensity of scattered light always increases exponentially, regardless of pump laser duration and crystal edge reflectivity. The expression of the growth coefficient G has been presented. The maximum fluence of Stokes can be as high as 10 J/cm2 approaching the damage threshold of KDP crystals, once the growth coefficient G exceeds 25, where the risk evaluation rule of TSRS in large-aperture, high fluence KDP crystal is defined.