稠密流体氦中的瑞利散射
Rayleigh scattering in dense fluid helium
摘要：
Iglesias等人（2002）指出，在冷的白矮星的大气中，氦原子的瑞利散射会因集体效应而减弱。他们的研究在这里扩展到考虑一个准确的评估原子的极化率和密度的影响，在瑞利截面在一个广泛的密度-温度区域。本文用散射强度分布方法计算了氦原子基态的动态偶极极化率。所考虑的振子强度的谱密度包括最重要的单和双激发跃迁到离散和连续能量。静态和动态极化率的结果与实验和其他理论评估显示出很好的一致性。此外，用Lorentz-Lorenz方程计算了氦的折射率，并与最近的实验结果进行了比较，结果令人满意。用蒙特卡罗模拟和代表粒子相互作用的有效能量势计算了原子的空间相关性对瑞利散射的影响，覆盖了密度在0.005和几g/cm $^3$之间，温度在$1000$ K和$15000$ K之间的流体。我们提供的解析拟合，流体氦的瑞利截面可以很容易地计算在波长$λ>505.35$ λ。碰撞诱导的光散射被估计为在密度大于1-2 g/cm $^3$（取决于温度）时的主要散射过程。
英文摘要：
Iglesias et al. (2002) showed that the Rayleigh scattering from helium atoms decreases by collective effects in the atmospheres of cool white dwarf stars. Their study is here extended to consider an accurate evaluation of the atomic polarizability and the density effects involved in the Rayleigh cross section over a wide density-temperature region. The dynamic dipole polarizability of helium atoms in the ground state is determinated with the oscillator-strength distribution approach. The spectral density of oscillator strength considered includes most significant single and doubly excited transitions to discrete and continuum energies. Static and dynamic polarizability results are confronted with experiments and other theoretical evaluations shown a very good agreement. In addition, the refractive index of helium is evaluated with the Lorentz-Lorenz equation and shows a satisfactory agreement with the most recent experiments. The effect of spatial correlation of atoms on the Rayleigh scattering is calculated with Monte Carlo simulations and effective energy potentials that represent the particle interactions, covering fluid densities between 0.005 and a few g/cm$^3$ and temperatures between $1000$ K and $15000$ K. We provide analytical fits from which the Rayleigh cross section of fluid helium can be easily calculated at wavelength $λ>505.35$ Å. Collision-induced light scattering was estimated to be the dominant scattering process at densities greater than 1-2 g/cm$^3$ depending on the temperature.
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