Godwin R P
Appl Opt. 1995 Jan 20;34(3):572-80. doi: 10.1364/AO.34.000572.
The Herpin theorem permits the reflectance of an arbitrary medium to be reproduced with a substrate of one complex refractive index overlaid with a coating film of a second complex refractive index and an appropriate thickness. The reflectances of a variety of laser-plasma-coupling experiments can be matched with a simple and physically meaningful procedure for choosing the fitting parameters. For short-pulse experiments, s-light coupling is dominated by substrate interactions at electron densities above critical and p-light coupling is dominated by resonance at the critical density. The weak dependence of resonance absorption on damping is the result of the harmonic-oscillator resonance form. As the plasma scale length becomes vanishingly small, the reflectance is that of the Fresnel equations, but surprisingly small plasma scale lengths have dramatic effects on the p-light reflectance. Film-substrate and WKB models predict similar resonance absorption, where both models are valid approximations and both should agree with multilayer and Helmholtz wave-optics calculations. For plasma scale lengths well below a wavelength, the film-substrate and the vacuum-heating models are closely related.
赫平定理允许用具有一个复折射率的基底覆盖一层具有第二个复折射率和适当厚度的涂膜来再现任意介质的反射率。各种激光 - 等离子体耦合实验的反射率可以通过一种简单且具有物理意义的程序来匹配，该程序用于选择拟合参数。对于短脉冲实验，在电子密度高于临界值时，s光耦合主要由基底相互作用主导，而p光耦合在临界密度时主要由共振主导。共振吸收对阻尼的弱依赖性是谐振子共振形式的结果。当等离子体尺度长度变得非常小时，反射率由菲涅耳方程给出，但令人惊讶的是，非常小的等离子体尺度长度对p光反射率有显著影响。薄膜 - 基底模型和WKB模型预测了相似的共振吸收，其中这两个模型都是有效的近似，并且都应与多层和亥姆霍兹波动光学计算结果一致。对于远低于一个波长的等离子体尺度长度，薄膜 - 基底模型和真空加热模型密切相关。
