Development of extreme-ultraviolet tunable coherent source

利用气体介质中的三阶非线性进行可调谐激光器的频率上转换，对于真空紫外区和紫外区的激光光谱是非常有用的。该项目的最终目标是在没有可调谐源的情况下，将可调范围扩大到72 nm以上。我们提出了如下方法来实现这一点：1)可调谐ArF和染料激光器之间的双光子共振四波混频，以及2)它们的拉曼移动线之间的共振四波混频。3年来的研究成果总结如下：1)利用氢气射流，将激光波长调谐在一条双光子共振线上，获得了高效的64 nm激光谐振三次谐波；2)通过与染料激光的混频，获得了低至66 nm的连续可调谐XUV相干辐射。这是迄今为止最短的可调谐激光波长记录。3)ARF激光器与喇曼频移谱线产生共振四波混频。然而，由Ante-Stokes谱线产生的较短波长尚未观察到。我们正在开发一种短脉冲高功率钛宝石激光器，以缩短可调谐范围。

Frequency up-conversion of tunable lasers using the 3rd order nonlineality in gaseous medium, is very useful for laser spectroscopy in the VUV and XUV region. The final target of this project is to extend the tunable range over 72nm where there was no tunable source. We proposed the following method to realize this : 1) two-photon resonant four-wave mixing between tunable ArF and dye lasers, and 2) resonant four-wave mixing between Raman shifted lines of them. Results of the project during these 3years are summarized as follows.1) Efficient resonant third harmonic generation of ArF laser was obtained at 64nm with hydrogen gas jet, when the laser wavelength was tuned on a two-photon resonant line.2) Then, by the mixing of dye laser beam with it, continuously tunable XUV coherent radiation down to 66nm was generated. This is the shortest wavelength record of tunable laser up to now.3) Resonant four-wave mixing between ArF laser and the Raman-shifted lines was generated. However, shorter wavelength generation by ante-Stokes lines has not yet observed. We are developing a short-pulse high -power Ti:sapphire laser to extend the tunable range shorter.