Tunable coherent light sources operating in the vacuum ultraviolet (VUV) region in the 100–200-nm (6–12 eV) wavelength range have important spectroscopic applications in many research fields, including time-resolved angle-resolved photoemission spectroscopy. 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 nanomembrane 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 nanomembranes of submicron thicknesses under excitation with visible femtosecond laser pulses. The submicron thickness of the nanomembranes is optimal for maximizing VUV generation efficiency and prevents self-phase modulation and spectral broadening of the fundamental beam. The observed VUV photons are up to 10⁷ photons per pulse at 157 nm with a 1-kHz repetition rate, corresponding to a conversion efficiency of 10⁻⁶. Moreover, the central VUV wavelength can be tuned in the 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 practical nonlinear media for VUV spectroscopic applications.

中文翻译：

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使用介电纳米膜在真空紫外区域可调谐产生三次谐波

在100-200 nm（6-12 eV）波长范围内的真空紫外（VUV）区域中工作的可调相干光源在许多研究领域中都有重要的光谱应用，包括时间分辨角度分辨光发射光谱。激光技术的最新进展已使可见的飞秒激光向上转换为真空和极紫外区域。但是，其实验装置的复杂性以及用于VUV生成的块状非线性晶体的稀缺性阻碍了其广泛使用。在这里，我们建议使用独立的电介质纳米膜作为可调VUV生成的简单实用方法。我们证明了从市场上可买到的SiO ₂产生足够高的三次谐波VUV光以用于光谱应用可见飞秒激光脉冲激发下亚微米厚度的纳米膜。纳米膜的亚微米厚度是最佳的，可以最大程度地提高VUV的产生效率，并可以防止自相位调制和基本光束的光谱展宽。观察到的VUV光子在157 nm处每个脉冲最多10 ^7个光子，重复频率为1 kHz，相当于10 ^-6的转换效率。此外，可以通过更改基本波长在146-190 nm波长范围内调整中心VUV波长。我们还将通过实验和计算来探索材料和厚度的依赖性。提出的结果表明，介电纳米膜可用作VUV光谱应用的实用非线性介质。