β-BBO, LBO, AND KTP Nonlinear Crystals as Sources of Millimeter-Wave Radiation

The refractive indices and the absorption coefficients of β-BBO, LBO, and KTP nonlinear optical crystals have been measured in the wavelength range of 0.5–3 mm at temperatures of 298 and 78 K. The absorption coefficients of all crystals at a wavelength of 1 mm do not exceed 3.5 cm–1 and fall with cooling. The anisotropy of the absorption coefficients of crystals increases significantly with decreasing wavelength ( 2 mm, it almost disappears. Upon cooling, the absolute values of the absorption coefficients fall below 0.2 cm–1. Based on the measured refractive indices, the collinear phase-matching curves are simulated numerically. The theoretical feasibility of IR (1.064 μm) laser radiation conversion into the millimeter-wave range is demonstrated.