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Study of 5%MgO:PPLN and CdSiP2 for infrared parametric generation

This work is devoted to the study of the nonlinear optical properties of 5%MgO:PPLN and CdSiP2, the motivation being the development of parametric optical sources in the second and third atmospheric transparency bands. These two crystals were cut as spheres in order to perform second harmonic generation and difference frequency generation in any direction of propagation by keeping normal incidence. Sphere experiments in 5%MgO:PPLN allowed us to validate at first the theory of angular quasi-phase-matching (AQPM), a general configuration corresponding to a waves propagation at any angle with respect to the grating vector. We experimentally confirmed that AQPM enables to provide wider spectral range and acceptance than birefringence phase-matching. Thanks to these measurements, it was also possible to refine the Sellmeier equations of 5%MgO:PPLN. The exhaustive nonlinear properties of CdSiP2 , a new nonlinear crystal, were measured over its whole transparency range. The possibility to generate wavelengths above 8 μm by difference frequency generation involving a pump wavelength at 1.064 μm was confirmed. The measurements of phase-matching directions of second harmonic generation and difference frequency generation allowed the Sellmeier equations to be refined. Finally, the optical damage threshold of CdSiP2 was measured and compared with AgGaS2, which is the main competitor for infrared generation above 8 μm. All the results that were obtained constitute a reliable basis for further studies devoted to the design of new infrared optical parametric devices.