Birefringence and absorption coefficients of alpha barium borate in terahertz range

In this paper we experimentally investigated the birefringence and absorption coefficients of alpha barium borate (alpha-BBO) crystal in the range of 0.3-10 THz by using a broadband air photonic terahertz time-domain spectrometer in both transmission and reflection modes. Several phonon modes were observed for o and e beams. The highest phonon mode at 6.8 THz has absorption coefficient of 1000 cm(-1). The comparison between the optical properties of the alpha-BBO and beta barium borate crystals showed that their phonon frequencies are different and alpha-BBO crystal has smaller refractive index, birefringence, and absorption coefficients in low frequency region. The blueshift behavior of the lowest phonon of the alpha-BBO crystal over the temperature range of 10-293 K has also been characterized. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3176965]