High-Efficiency and Wide-Band Single-Harmonic-Generation Properties of the New Crystal β-BaB 2 O 4

β-BaB2O4 was the inorganic nonlinear optical crystal possessing planar ring structure found first in our institute.1 Its space group is R3 with unit cell dimensions a = b = 12.532 A, c = 12.717 A, and 6 formula units in a hexagonal cell.2