Quasi-Phase Matching and Crystal Segmentation for Robust Optical Parametric Amplification

Nonlinear optical frequency conversion processes are very useful to generate new wavelengths or for amplifying a given signal wave at the expense of a stronger pump wave at a shorter wavelength. For such processes to occur efficiently the involved waves should be phase matched. However in general the related phase matching condition can be fulfilled exactly only for a single set of the waves’ wavelengths and for a unique propagation angle and temperature in the nonlinear medium. This is the main limitation for the using of such processes in connection with tunable sources or very short optical pulses with broadband spectrum. Fortunately some methods have been developed to overcome or limit this problem. The most notable one is represented by the chirped quasi-phase matching technique [1] , for which the period of quasi-phase matching (QPM) domain reversal evolves slowly along the crystal. The main drawback of this adiabatic approach is the requirement of very high pump intensities (possibly close to the damage threshold) and/or very long nonlinear crystals.