We report, for the first time to our knowledge, suppression of backward stimulated Raman scattering (BSRS) of picosecond pulses (57 ps, 532 nm) due to the development of optical breakdown in the surface (0 – 3 mm) water layer with a shift of the beam waist (lens focal length of 83 mm) to the water – air interface without changing the pump pulse energy (∼1.3 – 1.5 mJ). In this case, SRS generation in forward direction is observed even in the presence of breakdown. When the focal plane coincides with the surface, the BSRS generation is restored without optical breakdown, despite an increase in the pump radiation intensity due to a decrease in the beam diameter. It is significant that the optical breakdown threshold in the water volume was unattainable even with an increase in the pump pulse energy by more than an order of magnitude – up to 16 mJ. The mechanism of self-consistent summation of nonlinear optical processes, such as electrostriction, beam self-focusing, beam phase conjugation, and BSRS pulse compression is discussed.

中文翻译：

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将泵浦束腰从水体中移动通过表面时，水中皮秒脉冲的反向 SRS 抑制

据我们所知，我们首次报告了由于表面（0 – 3 毫米）水层发生光学击穿而导致的皮秒脉冲（57 ps，532 nm）的后向受激拉曼散射（BSRS）的抑制在不改变泵浦脉冲能量 (∼1.3 – 1.5 mJ) 的情况下，束腰（透镜焦距 83 mm）向水-空气界面的移动。在这种情况下，即使存在故障，也可以观察到正向 SRS 生成。当焦平面与表面重合时，尽管由于光束直径的减小泵浦辐射强度增加，但 BSRS 的产生在没有光学击穿的情况下得以恢复。重要的是，即使泵浦脉冲能量增加超过一个数量级（高达 16 mJ），水体积中的光击穿阈值也无法达到。