The French aerospace agency is involved in the realization of compact solid-state coherent sources, such as optical parametric oscillators (OPO), using new materials, such as highly non-linearly efficient semiconductors (ZnSe, GaAs or InP). However, since these materials are optically isotropic, they require new phase-matching techniques. We report the quasi-phase matched difference frequency generation in isotropic semiconductors using total internal reflection. We made use of large Fresnel birefringence at reflection between the signal and idler wave outputs of an OPO. Large tunability (between 8 and 13 μm) is demonstrated. Agreement between theoretical expectation and experimental results is excellent.
Among the mainly interesting parameters of an atomic vapor laser isotope separation process is the ionization yield. This parameter can be controlled as long as the laser beam spatial intensity distribution and temporal shape are well defined and not subjected to unexpected disturbing effects such as coherent propagation phenomena, leading to spatial and temporal reshaping with hot spots and pulse lengthening and delays. On the other hand, economical considerations require optically thick atomic columns which can favor such effects. In this work, we study the photoionization yield in atomic thulium vapor when propagation effects occur. We compare our experimental results with those of a coherent propagation code describing a four level system and including inhomogeneous broadening as well as degeneracies. We choose a three step photoionization scheme.
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