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

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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