Research on optical properties of warm dense matter using ultra-short-pulse lasers

本研究的目的是探索物质在新条件下的性质。利用超短脉冲激光，我们生产和研究高能量密度的物质，对应于1000 ~ 100,000开尔文的温度。尽管各种实验室技术可以产生非常高的能量密度，但产生的压力太高而无法限制，因此被加热的材料迅速膨胀。因此，开发高速（动态）诊断技术非常重要。短脉冲激光泵浦探测实验现在可以进行高重复率，并给出目标反射率变化的连续时间扫描期间和之后的热脉冲。探针脉冲持续时间提供了100秒的时间分辨率。一个单一的反射探针脉冲产生四个信号，这些信号表征了反射光的椭圆偏振，这种技术被称为“椭圆偏振”。我们还开发了新的计算机工具来分析或解释结果。在对低温金等离子体的实验分析中，我们发现了与电子局域化相一致的自由电子电导率的强烈降低的证据。Saha方程的解预测了异常等离子体组成，其中正离子Au+和负离子Au-与很少的自由电子平衡。低温等离子体异常低电导率的证据已经从其他实验技术中出现，包括直接测量脉冲加热系统（如线阵列、毛细血管等）的直流电导率。在某些情况下，量子分子动力学模拟也预测了低电导率。这项工作还没有准备好讨论热致密物质中的细节。相反，我们正在进行第一次定量探索，目的是确定主要的物理现象，特别是在金属-绝缘体跃迁、等离子体EOS基本思想的适用性、德鲁德电导率等方面。在不久的将来，我们将建立一个真实材料的许多原子极化率和介电函数的数据库，数据经过与实验的比较合格。少

The purpose of this research is to explore properties of matter at novel conditions. Using ultra-short pulse lasers, we produce and study matter at high energy density, corresponding to temperatures of 1,000〜100,000 Kelvin. Although very high energy densities can be created by various laboratory technologies, the resulting pressure is too high to confine and the heated material expands rapidly. For this reason it is important to develop high-speed (dynamic) diagnostic techniques.Short-pulse laser pump-probe experiments can now be performed with high repetition rate and give a continuous time scan of target reflectivity changes during and after the heat pulse. The probe pulse duration provides a time resolution 100fsec. A single reflected probe pulse yields four signals, which characterize the elliptic polarization of the reflected light, a technique called "ellipsometry". We also have developed new computer tools to analyze or interpret the results.In the analysis of experiments on low … More -temperature gold plasmas, we found evidence for a strong reduction of free-electron electrical conductivity consistent with localization of electrons. Solutions of the Saha equation predict an anomalous plasma composition in which positive ions Au+ and negative ions Au- are balanced with very few free electrons. Evidence for anomalous low conductivity in low-temperature plasmas has emerged from other experimental techniques including direct measurement of DC conductivities in pulse-heated systems such as wire arrays, capillaries, etc. Under certain circumstances, quantum molecular-dynamic simulations also predict low conductivity.This work is not yet ready to discuss the details in the warm dense matter. Rather we are making a first quantitative exploration with the goal of identifying the main physical phenomena, especially as regards metal-insulator transitions, applicability of basic ideas of plasma EOS, Drude conductivity, etc.In near future, we will have a database of many atomic polarizabilities and dielectric functions for real materials, data qualified by comparison to experiments. Less