The ultrasonic characterization of the propagation of femtosecond laser pulses in pure transparent water and colored phenol-red dye solutions at variable concentrations indicates their thermoacoustic pressure generation due to intrinsic multi-photon absorption in the low-power sub-filamentation regime and sub-linear pressure response of sub-critical plasma via free-carrier absorption in the filamentation regime. Multi-photon absorption appears to be concentration dependent for water and dye solutions, while plasma absorption demonstrates a universal trend for all these liquids. In the filamentation regime, through the non-linear laser-matter interactions, not only new optical frequencies (intense white-light supercontinua) were generated, but supercontinuum-based ultrafast broadband spectroscopy in the filaments also revealed many additional transient absorption bands of the dye molecules, induced via power-dependent and concentration-independent stimulated Raman scattering.

中文翻译：

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飞秒激光亚丝化和细丝化过程中吸收液体的电子和振动过程：超声和光学表征

飞秒激光脉冲在纯透明水和有色酚红色染料溶液中以可变浓度传播时的超声表征表明，由于低功率亚丝化过程中固有的多光子吸收和亚线性压力，它们产生了热声压亚临界等离子体在细丝化过程中通过自由载流子吸收的反应。多光子吸收似乎与水和染料溶液的浓度有关，而等离子体吸收则表明所有这些液体都有普遍的趋势。在灯丝化过程中，通过非线性的激光物质相互作用，不仅产生了新的光频率（强烈的白光超连续谱），