Non-linear crystals find applications where frequency conversion, sum or difference frequency generation, optical parametric generation or amplification is required. Typical nonlinear crystals are Lithium Triborate (LBO), Beta Barium Borate (BBO), Potassium Titanyl Phosphate (KTP), Potassium Dihydrogen Phosphate & Potassium Dideuterium Phosphate (KDP & DKDP), Lithium Iodate (LiIO3), Lithium Niobate (LiNbO3) and infrared nonlinear optical crystals such as AgGaS2, AgGaSe2, GaSe, ZnGeP2. Some nonlinear crystals for instance DKDP, BBO and KTP also possess electro-optical properties which make them useful for electro-optical applications, i.e., Q-switching or electro-optical amplitude modulation. In the selection of Nonlinear material, the most important thing while looking for non-linear crystals is conversion efficiency which in turn depends on effective nonlinear coefficient, crystal length, input power density and phase matching.