High-intensity laser pulses covering the ultraviolet to terahertz spectral regions are nowadays routinely generated in a large number of laboratories. In contrast, intense extreme-ultraviolet (XUV) pulses have only been demonstrated using a small number of sources including free-electron laser facilities and long high-harmonic generation (HHG) beamlines. Here, we demonstrate a concept for a compact intense XUV source based on HHG that is focused to an intensity of $2 \times {10^{14}} \,\,{{\rm W/cm}^2}$, with a potential increase up to ${10^{17}} \,\,{{\rm W/cm}^2}$ in the future. Our approach uses tight focusing of the near-infrared (NIR) driving laser and minimizes the XUV virtual source size by generating harmonics several Rayleigh lengths away from the NIR focus. Accordingly, the XUV pulses can be refocused to a small beam waist radius of 600 nm, enabling the absorption of up to four XUV photons by a single Ar atom in a setup that fits on a modest (2 m) laser table. Our concept represents a straightforward approach for the generation of intense XUV pulses in many laboratories, providing exciting opportunities for XUV strong-field and nonlinear optics experiments, for XUV-pump XUV-probe spectroscopy and for the coherent diffractive imaging of nanoscale structures.

中文翻译：

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紧凑型强极紫外光源

覆盖紫外到太赫兹光谱区域的高强度激光脉冲现在通常在大量实验室中产生。相比之下，强烈的极紫外 (XUV) 脉冲仅使用少量源进行了演示，包括自由电子激光设备和长高次谐波发生 (HHG) 光束线。在这里，我们展示了一个基于 HHG 的紧凑型强 XUV 源的概念，其聚焦强度为$2 \times {10^{14}} \,\,{{\rm W/cm}^2}$，其中可能增加到${10^{17}} \,\,{{\rm W/cm}^2}$将来。我们的方法使用近红外 (NIR) 驱动激光器的紧密聚焦，并通过在远离 NIR 焦点几个瑞利长度的地方生成谐波来最小化 XUV 虚拟源尺寸。因此，XUV 脉冲可以重新聚焦到 600 nm 的小束腰半径，使单个 Ar 原子能够在适合中等 (2 m) 激光台的设置中吸收多达四个 XUV 光子。我们的概念代表了在许多实验室中产生强 XUV 脉冲的直接方法，为 XUV 强场和非线性光学实验、XUV 泵 XUV 探针光谱和纳米级结构的相干衍射成像提供了令人兴奋的机会。