Development of an efficient XUV 64nm source using resonant third harmonic generation

目前还没有研制出波长小于100 nm的工业用极紫外(XUV)激光光源。在这个项目中，我们想要开发一种可用于工业应用的基于ArF准分子激光器的高重复频率XUV相干源。利用双光子共振三次谐波可以有效地产生64 nm的XUV辐射。当ArF激光聚焦到氢气射流中，并且波长被调谐到H_2的转动振动线之一时，XUV辐射被增强。研究了准分子激光流量、氢气射流密度和形状的优化。通过理论计算，包括电离吸收和位相匹配，得出沿光轴方向轮廓较薄、截面较宽的气体射流是较理想的，尝试通过两种方法确定XUV辐射的绝对能量：一种是Ar射流吸收XUV光子时的离子计数方法；另一种是探测系统光谱灵敏度的绝对定标方法。结果证实产生了1-4微焦耳/脉冲的XUV能量，并成功地完成了该项目。

Any extreme ultraviolet (XUV) laser source for industrial applications, whose wavelength is shorter than 100nm, has not been developed. In this project, we want to develop an XUV coherent source which can be used for industrial application, based on an ArF excimer laser with high repetition rate. XUV radiation at 64nm can be efficiently generated by two-photon resonant third harmonic generation. When an ArF laser beam is focused into a hydrogen gas jet and the wavelength is tuned at one of the rotational-vibrational line of H_2, XUV radiation is enhanced. We investigated the optimization of the excimer laser fluence, the density and the shape of H_2 gas jet. Theoretical calculation, including the absorption of ionization and the phase matching, shows that a gas jet with a profile of thin along the optical axis and wide in the cross section is preferable.We tried to determine the absolute energy of the XUV radiation by two methods : one is the ion counting when XUV photons are absorbed by an Ar jet, and the other is the absolute calibration of the spectroscopic sensitivity of the detecting system. As the result, XUV energy of 1-4muJ/pulse was confirmed to be generated, and we successfully finished the project.