KDP\DKDP倍频晶体吸收系数的斜入射测量

Absorption coefficient measurement of KDP or DKDP Frequency doubling crystal at oblique incidence

考虑惯性约束聚变系统中的磷酸二氢钾/磷酸二氘钾(KDP\DKDP)的吸收系数直接影响系统的转换效率及最终输出能量,本文研究了KDP\DKDP倍频晶体吸收系数的测量方法。提出了新的基于朗伯定律的倍频晶体吸收系数斜入射测量法。建立了斜入射状态下入射光偏振态与晶体o光和e光的关系模型,推导了小角度入射下晶体e光折射率的迭代计算方法。采用该方法计算了晶体的e光折射率,通过测量得到的数据间接计算出了KDP\DKDP倍频晶体吸收系数。详细分析了该方法在测量过程中的各项误差来源,得出该方法测量误差优于0.000 2cm^(-1)。最后,对一块40mm×40mm×60mm的开关晶体元件进行测试并与分光光度法比对以验证提出方法的可行性,结果显示两种测量方法的偏差小于0.000 2cm^(-1),表明该方法可用于惯性约束聚变系统中倍频晶体吸收系数的测量。

As the optical absorption coefficient of KDP or DKDP frequency doubling crystal in an Iner- tial Confinement Fusion （ICF） facility effects directly its frequency conversion efficiency and output energy, this paper researches the measurement methods of the absorption coefficients for two kinds of crystals. A measurement method based on LAMBERT-BEER law was proposed under oblique inci- dence for frequency doubling crystals. Then, the relationship between the polarization state of inci- dent light and the propagation of light in the crystals under oblique incidence was analyzed. An itera- tire algorithm for calculating extraordinary refractive index of the crystals was presented. On the basis of the iterative algorithm, the extraordinary refractive index was obtained and the optical absorption coefficient of KDP or DKDP frequency doubling crystal was calculated by using the measured dada in- directly. The error sources were analyzed in detail. It shows that total measuring error of this method is less than 0. 000 2 cm 1. Finally, a 40 mm×40 mm×60 mm crystal switch was measured and the ob- tained results were compared with that of spectrophotometry. The comparison indicates that the deviation of the two methods is less than 0. 000 2 cm 1, which verifies that the proposed method can be used in absorption coefficient measurement of KDP or DKDP frequency doubling crystal in the ICF facility.