Tunable third harmonic generation in the vacuum ultraviolet region using dielectric nanomembranes
Tunable third harmonic generation in the vacuum ultraviolet region using dielectric nanomembranes
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DOI：
10.1063/5.0008568
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发表时间：
2020-01
期刊：
影响因子：
5.6
通讯作者：
K. Konishi;D. Akai;Y. Mita;M. Ishida;J. Yumoto;M. Kuwata-Gonokami
中科院分区：
文献类型：
--
作者：
K. Konishi;D. Akai;Y. Mita;M. Ishida;J. Yumoto;M. Kuwata-Gonokami
在 100-200 nm (6-12 eV) 波长范围的真空紫外 (VUV) 区域工作的可调谐相干光源在许多研究领域具有重要的光谱应用，包括时间分辨角分辨光电子能谱 (ARPES)。激光技术的最新进展使可见飞秒激光能够上转换到真空和极紫外区域。然而，他们的实验装置的复杂性和用于产生 VUV 的体非线性晶体的稀缺阻碍了其广泛使用。在这里，我们建议使用独立式介电纳米膜作为一种简单实用的可调谐 VUV 生成方法。我们证明，在可见飞秒激光脉冲的激发下，市售的亚微米厚度的 SiO2 纳米膜可以产生足够强度的三次谐波 VUV 光，用于光谱应用。纳米膜的亚微米厚度对于最大化 VUV 产生效率是最佳的，并防止基波束的自相位调制和光谱展宽。观察到的 VUV 光子在 157 nm 处每脉冲高达 10^7 个光子，重复率为 1kHz，对应于 10^-6 的转换效率。此外，通过改变基波波长，可以在146-190 nm波长范围内调谐中心VUV波长。我们还通过实验和计算探索材料和厚度的依赖性。所提出的结果表明介电纳米膜可以用作真空紫外光谱应用的实用非线性介质。
Tunable coherent light sources operating in the vacuum ultraviolet (VUV) region in 100-200-nm (6-12 eV) wavelength range have important spectroscopic applications in many research fields, including time-resolved angle-resolved photoemission spectroscopy (ARPES). Recent advances in laser technology have enabled the upconversion of visible femtosecond lasers to the vacuum and extreme ultraviolet regions. However, the complexity of their experimental setups and the scarcity of bulk nonlinear crystals for VUV generation have hampered its widespread use. Here, we propose the use of a free-standing dielectric nanomembranes as a simple and practical method for tunable VUV generation. We demonstrate that third harmonic VUV light is generated with sufficient intensity for spectroscopic applications from commercially available SiO2 nanomemebranes of submicron thicknesses under excitation with visible femtosecond laser pulses. The submicron thickness of the nanomembranes is optimal for maximize the VUV generation efficiency and prevents self-phase modulation and spectral broadening of the fundamental beam. The observed VUV photons are up to 10^7 photons per pulse at 157 nm with 1-kHz repetition rate, corresponding to a conversion efficiency of 10^-6. Moreover, the central VUV wavelength can be tuned in 146-190-nm wavelength range by changing the fundamental wavelength. We also explore material and thickness dependence with experiments and calculations. The presented results suggest that dielectric nanomembranes can be used as a practical nonlinear media for VUV spectroscopic applications.