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）激光源。在本计画中，我们将研制一个可应用于工业上的超紫外相干光源，此光源是以高重复频率的ArF准分子激光器为基础。利用双光子共振三次谐波产生技术可以有效地产生64 nm的XUV辐射。当ArF激光束聚焦到氢气射流中，并将波长调谐到H_2的一条振转线上时，XUV辐射得到增强。研究了准分子激光能量密度、氢气射流密度和射流形状的优化。理论计算，包括电离吸收和相位匹配，表明沿光轴方向沿着较薄、截面较宽的气体射流是较好的。一种是当XUV光子被Ar射流吸收时的离子计数，二是对探测系统光谱灵敏度的绝对标定。实验结果表明，该装置可以产生1- 4 μ J/脉冲的超紫外能量，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.