Study on Dynamic Processes of Laser Desorption by Time-Resolved Luminescence Measurements

利用时间分辨发光测量系统研究了脉冲Nd: YAG激光辐照解吸物质的空间分布及其时间演化。测量包括三种构型；光谱-时间，时空和单色时空测量。最后一种是在本研究中发展起来的。得到了以下结果：红外激光（λ =1064nm, 100J/cm^2）在空气中的石墨靶和He气体上产生的羽流有三个组成部分；等离子体，由等离子体和碳自由基驱动的冲击波。这些成分产生的机制已被阐明。紫外激光（λ =266nm, 5J/cm^2）在Si （ll）表面上产生的羽流和高真空烧结的NiO球团分离成三个组分；速度分别为10^6,10^5和10^4m/s的电子、离子和中性原子。离子比中性原子运动得快得多，因为从等离子体中逸出的电子加速了离子的运动。得到了中性原子速度与极性角的关系。在低于阈值（lJ/cm^2）的紫外激光照射下，从Si （lll）表面解吸的物质呈缓慢移动（10^3m/s）的群体，速度分布较宽。上述结果表明，本研究开发的测量系统为我们提供了有关激光解吸抛射物质动力学过程的有用信息。具体地说，该系统的高灵敏度通过检测到不可观察的物种这一事实得到了验证。然而，作为本研究最终目标的吸附物质的检测尚未完成。

The spatial distribution of desorbed species to pulsed Nd : YAG laser-irradiation and its temporal evolution have been investigated with time-resolved luminescence measurement system. The measurements included three configurations ; spectrum-time, space-time, and monochromatic space-time measurements. The last one has been develped in this study. Following results have been obtained.1. The plumes which are produced by IR laser (lambda=1064nm, 100J/cm^2) above graphite targets in the air and He gas have three components ; plasma, shock wave driven by the plasma and carbon radicals. The mechanisms for the generation of these components have been clarified.2. The plumes which are produced by UV laser (lambda=266nm, 5J/cm^2) above Si (lll) surfaces and sintered NiO pellets in high vacuum are separated into three components ; electrons, ions and neutral atoms whose velocities are 10^6,10^5 and 10^4m/s, respectively. Ions move much faster than neutral atoms because of acceleration by electrons which escaped from the plasma. Polar angle-dependence of the velocity of neutral atoms has been obtained.3. Species desorbed from Si (lll) surfaces under the irradiation of UV laser of below threshold fluence (lJ/cm^2) were detected as a group moving slowly (10^3m/s) with wide velocity distribution.Above results show that the measurement system developed in this study provides us with useful information about dynamical processes of species ejected by laser desorption. Specifically, high sensitivity of this system is verified by the fact that the species which are not observable have been detected. However, detection of adsorbed species, which is the ultimate goal of this study, has not yet accomplished.