“…1,2 Since the first SHG experiment, performed by Franken et al 3 in 1961, the conversion efficiency has been improved by utilizing higher power lasers, phasematching ͑PM͒ techniques and superior nonlinear crystals, such as KTiOPO 4 ͑KTP͒, 4 RbTiOPO 4 , 5 and their isomorphs from the titanyl arsenate family. 6 KTP-type crystals continue to be extremely popular for SHG as they are capable of both type-I and type-II PM over a wide range of temperatures.…”