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

用时间分辨发光测量系统研究了脉冲激光辐照下的解吸物种的空间分布及其时间演化。测量包括三种配置：光谱-时间、空间-时间和单色时空测量。最后一个是在本研究中发展起来的。取得了以下成果：1.红外激光(波长1064 nm，100J/cm~2)在空气和氦气中的石墨靶上方产生的羽流有三种成分：等离子体、由等离子体驱动的冲击波和碳自由基。已经澄清了产生这些组成部分的机制。用波长为266 nm，5J/cm~2的紫外光激光在高真空条件下在Si(111)表面和NiO烧结球表面产生的羽流被分成电子、离子和中性原子三个组分，其速度分别为10^6、10^5和10^4m/S。由于从等离子体中逸出的电子的加速，离子的运动速度比中性原子快得多。得到了中性原子运动速度的极角依赖关系。在低于阈值注量(LJ/cm2)的紫外光照射下，从Si(111)表面解吸的物种以一群速度分布较宽的缓慢运动(10^3m/S)的形式被探测到。这一结果表明，本研究建立的测量系统为我们提供了激光脱附物种的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未观察到的物种的事实来验证。然而，这项研究的最终目标--吸附物种的检测还没有完成。

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.