A novel optical switch for second harmonic generation(SHG) is presented based on the electro-optical switching effect of polymer dispersed liquid crystal(PDLC) and nonlinear optical characteristics of KIO3 powder.YAG laser pulse enters the SHG optical switch,at the same time,an ac electric field is applied on PDLC for modulation.When the switch is in off-state,the second harmonic light is restrained.When the switch is in on-state,the second harmonic waves of YAG laser are generated and detected in the scatt...