Resonance states of axion-like particles were searched for via four-wave mixing by focusing two-color pulsed lasers into a quasi-vacuum. A quasi-parallel collision system that allows probing of the sub-eV mass range was realized by focusing the combined laser fields with an off-axis parabolic mirror. A 0.10 mJ/34 fs Ti:Sapphire laser pulse and a 0.14 mJ/9 ns Nd:YAG laser pulse were spatiotemporally synchronized by sharing a common optical axis and focused into the vacuum system. No significant four-wave mixing signal was observed at the vacuum pressure of $3.7 \times 10^{-5}$ Pa , thereby providing upper bounds on the coupling-mass relation by assuming exchanges of scalar and pseudoscalar fields at a 95 % confidence level in the mass range below 0.21 eV. For this search, the experimental setup was substantially upgraded so that optical components are compatible with the requirements of the high-quality vacuum system, hence enabling the pulse power to be increased. With the increased pulse power, a new kind of pressure-dependent background photons emerged in addition to the known atomic four-wave mixing process. This paper shows the pressure dependence of these background photons and how to handle them in the search.

中文翻译：

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在高质量真空系统中通过四波混合与准平行激光对撞机扩展搜索亚 eV 轴子共振

通过将两色脉冲激光聚焦到准真空中，通过四波混合搜索轴子状粒子的共振态。通过使用离轴抛物面镜聚焦组合激光场，实现了允许探测亚 eV 质量范围的准平行碰撞系统。0.10 mJ/34 fs Ti:Sapphire 激光脉冲和 0.14 mJ/9 ns Nd:YAG 激光脉冲通过共享公共光轴在时空上同步并聚焦到真空系统中。在 $3.7 \times 10^{-5}$ Pa 的真空压力下没有观察到显着的四波混合信号，从而通过假设标量和伪标量场在 95% 置信水平的交换提供了耦合质量关系的上限在低于 0.21 eV 的质量范围内。对于这次搜索，实验装置大幅升级，使光学元件符合高质量真空系统的要求，从而提高脉冲功率。随着脉冲功率的增加，除了已知的原子四波混合过程之外，还出现了一种新的压力相关背景光子。本文展示了这些背景光子的压力依赖性以及如何在搜索中处理它们。