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

我们对高效产生真空紫外光的新方案、光脉冲的传播动力学以及产生的真空紫外光的可能应用进行了理论研究。由于篇幅所限，我们在这里介绍了我们的项目最重要的成果，即对新提出的用于高效产生VUV光的光纤混频方案进行了理论分析：众所周知，通过频率转换产生的波的再吸收过程是阻碍转换效率提高的最关键的限制因素。为了解决这一根本问题，我们利用了自动电离状态。自电离共振总是伴随着位于附近的吸收极小值，这是由于自电离态的原子相干引起的量子力学干涉。因此，如果对入射激光频率进行调谐，使得所产生的波的频率与跃迁频率…一致从初始状态到最终(自动电离)状态的吸收最小的Cy越多，再吸收就可以被显著抑制。我们的详细分析表明，转换效率可以提高三个数量级。首先，利用激光诱导等离子体发射线中的自逆吸收，我们发展了一种新的方法来确定相应的上、下态的位置相关密度，并将其应用于Al等离子体。其次，我们研制了基于准分子泵浦染料激光器放大连续波环形染料激光器的窄带脉冲染料激光系统。这种窄带激光器使我们能够通过光学探测来研究激光烧蚀物种的平移速度的变化。我们发现，在缓冲气体中烧蚀后几微秒的时间尺度内，烧蚀物种的平移速度呈现脉动。较少

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