Liang Xiao-Xuan, Zhang Zhenxi, Vogel Alfred
Opt Express. 2019 Feb 18;27(4):4672-4693. doi: 10.1364/OE.27.004672.
We study the energy spectrum of laser-induced conduction band (CB) electrons in water by multi-rate equations (MRE) with different impact ionization schemes. Rethfeld's MRE model [Phys. Rev. Lett.92, 187401(2004)Phys. Rev.B 79, 155424(2009)], but the corresponding rate equations are computationally very expensive. We introduce a simplified splitting scheme and corresponding rate equations that still agree with energy conservation but enable the derivation of an asymptotic SRE. This approach is well suited for the calculation of energy spectra at long pulse durations and high irradiance, and for combination with spatiotemporal beam propagation/plasma formation models. Using the energy-conserving MREs, we present the time-evolution of CB electron density and energy spectrum during femtosecond breakdown as well as the irradiance dependence of free-electron density, energy spectrum, volumetric energy density, and plasma temperature. These data are relevant for understanding photodamage pathways in nonlinear microscopy, free-electron-mediated modifications of biomolecules in laser surgery, and laser processing of transparent dielectrics in general.
我们通过采用不同碰撞电离方案的多速率方程（MRE）来研究水中激光诱导导带（CB）电子的能谱。采用了雷思费尔德的MRE模型[《物理评论快报》92, 187401(2004)；《物理评论B》79, 155424(2009)]，但其相应的速率方程计算成本非常高。我们引入了一种简化的分裂方案和相应的速率方程，该方案仍符合能量守恒，且能推导出渐近单速率方程（SRE）。这种方法非常适合计算长脉冲持续时间和高辐照度下的能谱，以及与时空光束传播/等离子体形成模型相结合。使用能量守恒的MREs，我们展示了飞秒击穿过程中CB电子密度和能谱的时间演化，以及自由电子密度、能谱、体积能量密度和等离子体温度的辐照度依赖性。这些数据对于理解非线性显微镜中的光损伤途径、激光手术中生物分子的自由电子介导修饰以及一般透明电介质的激光加工具有重要意义。
