Relaxation of Dense Electron Plasma Induced by Femtosecond Laser in Dielectric Materials

Electron plasma induced by a focused femtosecond pulse （130 fs, 800 nm） in dielectric materials （Soda Lime glass, K9 glass, and SiO2 crystal） is investigated by pump-probe shadow imaging technology. The relaxation of the electron plasma in the conduction band is discussed. In SiO2 crystals, a fast self-trapping process with a trapping time of 150fs is observed, which is similar to that in fused silica. However, in Soda Lime glass and K9 glass, no self-trapping occurs, and two decay processes are found： one is the energy relaxation process of conduction electrons within several picoseconds, another is an electron-hole recombination process with a timescale of lOOps. The electron collision time T in the conduction band is also measured to be in the order of 1 fs in all of these materials.     

用偏最小二乘法—荧光光谱法定量分析芳烃混合物

本文用偏最小二乘法方法来解析荧光的激发发射和左阵，直接定量分析荧光混合物试样。文中分析了ＥＥＭ的特点，介绍了用ＥＥＭ－ＰＬＳ定量分析试样的思路和方法，并对５个模拟混合物和４个实际混合物进行了测试和计算，获得了满意的结果。本文还用实例讨论了数据中的异常点，对结果的影响及晚年剔除的方法。     

Ultra-Fast Decay Process of Electrons in LiNbO3 Crystal Induced by Femtosecond Pulse

Temporal evolution of absorption induced by single femtosecond pulse （13Ors, 800nm） with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141 ps and it is attributed to the direct interband electron-hole recombination process.     

Lengthening the Lifetime of Long Plasma Channel in Air Generated by Femtosecond Laser Pulse

We theoretically investigate the lifetime of self-guided plasma channel in air by launching an auxiliary delayed long-pulsed laser beam following an ultrashort laser. A detailed model makes the electron-ion recombination, the attachment of electrons on neutral particles, and particularly the impact ionization and electron-detachment mechanism incorporate. The calculated results show that the temporal evolution of electron density is greatly flattened and broadened. When the auxiliary laser intensity exceeds the threshold 3.32 × 10^4 Wcm^-2, the channel lifetime is distinctly prolonged from nanosecond to microsecond, or even longer due to the electrical field enhancement. Furthermore, with the laser intensity up to 109 Wcm^-2, the impact ionization overwhelms the detachment in effect. Thus, it is an effective way to extend the channel lifetime and provides a real opportunity for applications.