Although the dielectric constant of plasma depends on electron collision time as well as wavelength and plasma density, experimental studies on the electron collision time and its effects on laser-matter interactions are lacking. Here, we report an anomalous regime of laser-matter interactions generated by wavelength dependence (1.2–2.3 µm) of the electron collision time in plasma for laser filamentation in solids. Our experiments using time-resolved interferometry reveal that electron collision times are small (<1 femtosecond) and decrease as the driver wavelength increases, which creates a previously-unobserved regime of light defocusing in plasma: longer wavelengths have less plasma defocusing. This anomalous plasma defocusing is counterbalanced by light diffraction which is greater at longer wavelengths, resulting in almost constant plasma densities with wavelength. Our wavelength-scaled study suggests that both the plasma density and electron collision time should be systematically investigated for a better understanding of strong field laser-matter interactions in solids.

尽管等离子体的介电常数取决于电子碰撞时间以及波长和等离子体密度，但仍缺乏对电子碰撞时间及其对激光与物质相互作用影响的实验研究。在这里，我们报告了固体中激光细丝化过程中等离子体碰撞电子的波长依赖性（1.2-2.3 µm）所产生的激光物质相互作用的异常机制。我们使用时间分辨干涉仪进行的实验表明，电子碰撞时间很小（<1飞秒），并且随着驱动器波长的增加而减少，这创建了以前无法观察到的等离子体中光散焦的机制：较长的波长具有较少的等离子体散焦。这种异常的等离子体散焦可以通过较长的波长处更大的光衍射来抵消，导致随波长几乎恒定的等离子体密度。我们的波长规模研究表明，应系统地研究等离子体密度和电子碰撞时间，以更好地了解固体中的强场激光物质相互作用。