Nonlinear optics in the VUV region utilizing autoionizing resonance of metallic atoms

我们对一种有效产生紫外光的新方案、光脉冲的传播动力学以及产生的紫外光的可能应用进行了理论研究。由于空间所限，我们在此描述本项目最重要的成果，即对新提出的有效产生VUV光的光纤混频方案的理论分析：众所周知，通过频率转换产生的波的重吸收过程是提高转换效率的最关键限制因素。为了解决这个基本问题，我们利用了自电离态。自电离共振总是伴随着位于附近的吸收最小值，这是由于自电离态原子相干性的量子力学干涉。因此，如果调谐入射激光频率，使产生的波的频率与跃迁频率一致，从初始状态到最终（自电离）状态的吸收最小值，可以显著抑制重吸收。我们的详细分析表明，转换效率可以提高三个数量级。至于实验，有三个重要的发现。首先，利用激光诱导等离子体发射谱线中的自反向吸收，我们开发了一种新的方法来确定相应上下态的位置依赖密度，并将其应用于铝等离子体。其次，我们开发了一种窄带脉冲染料激光系统，该系统是基于连续波环形染料激光被准分子泵浦的放大。这种窄带激光器使我们能够通过光学检测来研究激光烧蚀物质的平移速度变化。我们发现，在缓冲气体中烧蚀后几微秒的时间尺度内，烧蚀物质的平移速度表现出脉动。少

We have carried out theoretical research on a new scheme for the efficient generation of VUV light, propagation dynamics of light pulses, and possible applications of the generated VUV light. Because of the space limitation, we describe here the most important achievement of our project, namely the theoretical analysis of the newly proposed fbrwave mixing scheme for the efficient generation of VUV light : it is well known that the re-absorption processes of the generated wave through frequency conversion is the most crucial limiting factor against increasing the conversion efficiency. In order to solve this essential problem, we have utilized an autoionizing state. An autoionizing resonance is always accompanied by an absorption minimum located nearby, which is due to the quantum mechanical interference via atomic coherence of an autoionizing state. Therefore, if the incident laser frequencies are tuned such that the frequency of the generated wave coincides with the transition frequen … More cy from the initial state to the absorption minimum of the final (autoionizing) state, re-absorption can be significantly suppressed. Our detailed analysis has shown that the conversion efficiency can be improved by three orders of magnitude.As for experiments, there are three important findings. First, by making use of a self-reversed absorption in an emission line of laser-induced plasma, we have developed a new method to determine the position-dependent densities of the corresponding upper and lower states, and applied it to the Al plasma. Second, we have developed a narrow-band pulsed dye-laser system, which is based on the amplification of a CW ring dye-laser by an excimer-pumped dye-laser. This narrow-band laser enables us to investigate the change of the translational velocity of laser-ablated species through optical detection. We have found that, in the time scale of a few microsecond after ablation in a buffer gas, the translational velocities of the ablated species exhibit pulsation. Less