Nonlinear optical (NLO) crystals are the key materials for the development of laser science and technology because only these kinds of materials have functions to change frequency of laser beam and modulate it in amplitude and phase. It may be said that lasers could not be used so widely in modern science and technology as they have been today, without NLO crystals. Development of NLO crystals with better linear optical (LO) and NLO properties, wider spectral transmission, and phase-matching range in particular is obviously essential for further widening the application field of lasers,...