Terahertz optical properties of LBO crystal upon cooling to liquid nitrogen temperature

The anisotropy of optical properties of nonlinear lithium borate (LBO) crystals in the range of 0.2 - 2 THz is investigated by time-domain THz spectroscopy at room temperature and at T = 81 K. It is shown that the birefringence dramatically decreases upon cooling, as a result of which phase-matching conditions cannot be implemented. At the same time, the absorption coefficients a(x) and a(y) are found to decrease significantly with decreasing temperature, due to which the LBO crystal becomes a promising material for generating THz radiation via optical rectification and fabricating periodic structures and optical elements.