Study of low temperature matrix crystals as non-linear optical elements

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Coherent light sources in the wide frequency region are developed by using of high power pulse laser and non-linear optical effects like harmonics-, sum-, difference-generation, four waves mixing and parametric oscillation. In the sohrt wave length region, for example, non-linear materials like BBO crystal generates the radiation down to 210 nm in good efficiency. However, solid state materials have an inevitable self-absorption in shorter wave lenght than 210 nm. Therefore, rare gas atoms or metal vapor in the gas phase are alternated to generate the shorter wave length radiation. However their conversion efficiencies are quite small (at most 10^<-6>) because of low density and lack of phase matching condition in the gas phase.In order to remove the problem of low density, a low temperature matrix of the rare gas atom was proposed to use as a non-linear optical device for generating the shorter wave length radiation and tried in this research. We have succeeded in making transparent crystal of some rare gas atoms and molecules at low temperature. Using the large non-linear optical property of Xe, its pure crystal were used itself as a non-linear optical device. Non-linearity of the crystal was directly investigated by detecting the third order harmonic generation of pulse laser of 532 and 355 nm from a single mode YAG laser. The harmonics in the vacuum ultra-violet region were detected by a monochromater and solar-blind photomultiplier. The second order harmonics of 355 nm and the third harmonics of 532 nm were strongly generated from the surfaces of the crystal. On the other hand, the third order of 355 nm was weakly generated homogeneously in the crystal. The former emission may be related to the Xe_2 exicimer molecule. Thus we could confirm the possibility of the rare gas crystal as non-linear materials in the VUV region.