Chen Xinxin, Zhou Qing, Wang Zhongyang
Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Molecules. 2025 Apr 29;30(9):1969. doi: 10.3390/molecules30091969.
Two components of X-waves, near-axis and off-axis, were observed in the generation of second-order Stokes around 550 nm, excited by intense 400 nm, 100 fs pump pulses in a 50 cm water cuvette. The emission angles of these two X-waves exhibited different evolutions; when the pump energy increased, the emission angle of the near-axis X-wave increased, while that of the off-axis X-wave decreased. These abnormal features of second-order X-waves came from the four-wave mixing process, accompanied by induced intense hydrated electrons via cascade ionization. The induced wave vector from high-density hydrated electrons led to angle-dependent phase-matching for the generation of the off-axis X-wave. However, for the generation of the near-axis X-wave, the induced wave vector from hydrated electrons initially compensated for the phase mismatch at a low pump energy, but as the energy increased, the phase mismatch also increased. Moreover, anomalous Raman shifts at second-order Stokes wavelengths (3262 cm and 3350 cm) exhibited a similar evolutionary process to the anomalous Raman peaks at the Stokes wavelengths. The shifts arose from excess electrons being injected into the hydrogen bond network of water clusters.
在一个50厘米长的水槽中，用强400纳米、100飞秒的泵浦脉冲激发时，在550纳米附近的二阶斯托克斯光产生过程中观察到了X波的两个分量，即近轴分量和离轴分量。这两个X波的发射角呈现出不同的演化；当泵浦能量增加时，近轴X波的发射角增大，而离轴X波的发射角减小。二阶X波的这些异常特征源于四波混频过程，伴随着通过级联电离产生的强水化电子。来自高密度水化电子的感应波矢导致了离轴X波产生的角度相关相位匹配。然而，对于近轴X波的产生，水化电子的感应波矢最初在低泵浦能量下补偿了相位失配，但随着能量增加，相位失配也增加。此外，二阶斯托克斯波长（3262厘米和3350厘米）处的异常拉曼位移与斯托克斯波长处的异常拉曼峰呈现出相似的演化过程。这些位移源于过量电子注入到水团簇的氢键网络中。
