CO_(2)激光放大器增益与种子光光强匹配特性分析

Analysis of Matching Characteristics of CO_(2)Laser Amplifier Gain and Seed Beam Intensity

为了提升激光等离子体极紫外光刻机光源中高重复频率、短脉冲CO_(2)主振荡功率放大系统能量提取效率,需开展种子光光强截面分布与激光放大器增益分布的耦合匹配特性研究。基于欧拉-拉格朗日公式与Frantz-Nodvik方程,采用变分法求解了特定增益分布下最优种子光光强分布函数,研究了种子光半径、种子光光强分布与放大器增益分布对功率提取效率的影响。数值模拟表明:当脉冲种子光功率为500 W时,基模高斯光束的最优光束半径为0.54 cm,低功率种子光的最优光束半径与放大器增益宽度不相等;当脉冲种子光功率为2000 W时,高阶超高斯光束的最优光束半径接近增益区域半径,8阶超高斯光束对应的最佳光束半径为0.9 cm,功率提取值为3409 W,采用高阶的增益分布和与之匹配的超高斯光束能够极大提升放大器的能量提取值。该研究结果将为脉冲CO_(2)主振荡功率放大系统的设计提供理论指导。

To improve the energy extraction efficiency of the high repetition rate and short pulse CO_(2)master-oscillator power-amplification system in the light source of laser plasma extreme ultraviolet lithography,it is necessary to study the coupling matching characteristics between the beam intensity cross-section distribution of the seed beam and the gain distribution of the laser amplifier.Based on the Euler-Lagrange formula and Frantz-Nodvik equation,the optimal intensity distribution function of the seed beam under a specific gain distribution is solved by variational method.The effects of the seed beam width,intensity distribution,and gain distribution of the laser amplifier on the power extraction are examined.The results of numerical simulation show that for the laser amplifier with a gain radius of 1 cm,the optimal beam radius of the fundamental mode Gaussian beam with a pulsed seed light power of 500 W is 0.67 cm,and the optimal beam width of the low-power seed light is not equal to the gain width of the amplifier.The optimal beam radius of the higher-order super-Gaussian beam with a pulsed seed power of 2000 W is close to the gain region radius.The optimal beam radius corresponding to the 8-order super-Gaussian beam is 0.9 cm,and the power extraction value is 3409 W.The higher-order gain distribution and the matched super-Gaussian beam can significantly enhance the energy extraction value of the amplifier.The results of this study will provid e theoretical guidance for designing pulsed CO_(2)main-oscillation power amplifier systems.