Kaliumtitanylphosphat (KTiOPO4) is an excellent non-linear crystal known for its high NLO coefficient. It exhibits high optical quality, broad transparent range, relatively high effective SHG coefficient (about 3 times higher than that of KDP), very high optical damage threshold, wide acceptance angle, small walk-off and type I and type II non-critical phase-matching (NCPM) in a wide wavelength range. It is being used for frequency doubling of Nd:YAG lasers and other Nd-doped lasers, particularly at the low or medium power density. The most popular application is for Second Harmonic Generation (SHG) and Optical Parametric Oscillators (OPO). Temperature-noncritical phase matching is available for many Nd-doped active elements!