In recent years, significant advancements in high-repetition-rate, high-average-power mid-infrared laser pulses have enabled the generation of tabletop high-flux coherent soft x-ray harmonics for photon-hungry experiments. However, for practical applications, it is crucial to effectively filter out the driving beam from the high harmonics. In this study, we leverage the distinctive properties of a Bessel–Gauss (BG) beam to introduce a novel approach for spatial filtering, specifically targeting soft x-ray harmonics, releasing with a high-photon flux simultaneously. Our simulations reveal that by finely adjusting the focus geometry and gas pressure, the BG beam naturally adopts an annular shape, emitting high harmonics with minimal divergence in the far field. To achieve complete spatial separation of the driving beam and harmonic emissions, we pinpoint the optimal gas pressure and focusing geometry, particularly under overdriven laser intensities, for achieving good phase matching of harmonic emissions from short-trajectory electrons within the gas medium when the exact ionization level is higher than the “critical” value. Additionally, we establish scaling relations for sustaining optimal phase-matching conditions crucial for spatially separating the driving laser and the high-harmonic field, especially as the wavelength of the driving laser increases. Furthermore, our analysis demonstrates a substantial enhancement of harmonic yields by at least one order of magnitude compared to a truncated Gaussian annular beam. We also show that under accessible experimental conditions, soft x-ray photon flux up to 1010 photons/s at 250 eV can be achieved. The utilization of the BG beam opens up a promising pathway for the development of high-flux attosecond soft x-ray light sources, poised to serve a wide range of applications.

中文翻译：

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使用贝塞尔-高斯光束进行空间滤波和最优生成高通量软 X 射线高谐波


近年来，高重复率、高平均功率中红外激光脉冲的重大进展使用于高光子实验的台式高通量相干软 X 射线谐波成为可能。然而，对于实际应用，从高次谐波中有效滤除驱动光束至关重要。在这项研究中，我们利用贝塞尔-高斯 （BG） 光束的独特特性，引入了一种新的空间滤波方法，专门针对软 X 射线谐波，同时以高光子通量释放。我们的仿真表明，通过微调聚焦几何形状和气体压力，BG 光束自然地采用环形形状，发射高谐波，在远场中的发散最小。为了实现驱动光束和谐波发射的完全空间分离，我们确定了最佳气体压力和聚焦几何形状，特别是在过驱动激光强度下，以便在精确电离水平高于“临界”值时实现气体介质内短轨迹电子的谐波发射的良好相位匹配。此外，我们建立了缩放关系以维持最佳相位匹配条件，这对于在空间上分离驱动激光器和高谐波场至关重要，尤其是在驱动激光器的波长增加时。此外，我们的分析表明，与截断的高斯环形光束相比，谐波产率至少提高了一个数量级。我们还表明，在可接近的实验条件下，在 250 eV 时可以实现高达 1010 光子/秒的软 X 射线光子通量。 BG 光束的利用为高通量阿秒软 X 射线光源的开发开辟了一条有前途的途径，有望为广泛的应用提供服务。