Thesis (M.Sc.) - Cairo University - National Institute of Laser Enhanced Sciences - Department of Laser Sciences and Interaction

Recently, the fabrication of nonlinear crystals has developed to such extent that we can get high optical damage threshold, moderate optical nonlinearity, and favorable phase-matching properties of these crystals. This has led to important breakthroughs in optical parametric oscillation (OPO) devices, particularly in the pulsed high-intensity operating regime, enabling the development of a wide range of practical systems and their deployment in new applications. However, the limited IR-transparency of Beta Barium Borate (Ý-BaB₂O₄) crystal (BBO) and Lithium tri-borate (LiB₃O₅) crystal (LBO) confined the wavelength coverage of the majority of practical OPO devices to the visible and NIR at wavelengths typically below{u223C}2 {u1D707}{u1D45A}. In this work, 2-parametric processes of nonlinear crystals were investigated, most notably BBO and LBO non-linear crystals. A preset optical parametric generation (OPG) system based on BBO crystal (uniaxial, type I phase matching) with non-collinear waves was used. The system was pumped by diode pumped solid state (DPSS) laser (blue diode laser of 405 nm wavelength) having the nonlinear output in the form of a down converted photons at which one photon is splitted into two photons with lower frequencies (signal and idler). The degenerate case was carefully studied where both photons have 810 nm wavelength with the same polarizations. The cones formed by both types signal and idler were also studied. Furthermore, an experimental setup for an OPO system in degenerate case was designed and built based on a nonlinear crystal. An LBO crystal -(bi-axial, type I phase matching crystal) was used and pumped by a Q-switched Nd: YAG at the second harmonic 532 nm wavelength. The generation of 1064 nm wavelength was studied. Generally, tuning the OPO was done by changing the phase matching angle and consequently re-tuning the laser cavity. The margin between the crystal damage threshold and the OPO laser threshold was considerably narrow, which in turn implied a careful choice of the parameters. Cavity parameters of degenerate optical parametric oscillator xvii (DOPO) system (standing waves modes, beam shape and stability diagrams) were optimized using LASCAD program

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