Sum-frequency generation of extreme-UV light 朱旭新 ^{1*}, 汪治平^{2}^{1}物理系, 中央大學, 桃園市, Taiwan^{2}原子與分子科學研究所, 中央研究院, 台北市, Taiwan* presenting author:Hsu-hsin Chu, email:hhchu@ncu.edu.tw According to the advance of high-power laser technology, ultra-short coherent extreme-ultraviolet (EUV) and soft x-ray sources can be driven directly from the laser-plasma interaction, such as EUV/soft x-ray lasers and high-harmonic generation. Therefore, the nonlinear wave-mixing process now is possible to be extended to such short wavelengths. In this presentation, we propose that rare gas ions are proper interacting medium. For example, if the argon atom is ionized to be Ar
^{3+} ion, the ionization potential of the forth electron is 59.81 eV. Then the EUV photons with photon energy less than 59.81 eV (wavelength > 20.7 nm) will not be absorbed, as a result of that photoionization cannot occur. However, the residual electrons can still provide the nonlinear response for nonlinear wave-mixing. By using Cowan’s atomic structure code, we calculate the dipole matrix elements of Ar^{3+} ions, and then its third-order nonlinear polarizability for sum-frequency generation of two IR photons (800 nm) and one EUV photons (45 nm). The result is about 3.16 × 10^{−63} coul-m^{4}/volt^{3}. After that, we propose an experiment incorporated with one 50-mJ, 30-fs IR pulse, one 1-μJ, 20-fs EUV pulse, and an Ar gas jet with 10^{17} cm^{−3} density. The calculation shows that the energy of the sum-frequency generation output can reach 1 nJ, corresponds to 0.1% conversion efficiency. This is a promising method for the manipulation of EUV waves.Keywords: extreme-ultraviolet, sum-frequency generation, nonlinear wave-mixing |