NLO crystal: BBO, BIBO, KDP-DKDP, KTP, LiNbO3 and MgO-LiNbO3, they are usually used to harmonic generation; Birefringent Crystal: a-BBO, Calcite and YVO4; Laser Crystal: ND-GdVO4, ND-YAG and ND-YV04; E-O Crystal: LiNbO3 SAW Wafer; Passive Crysta:Cr4+: YAG.