Birefringence of β-BaB2O4 crystal in the terahertz region for parametric device design

beta-BaB(2)O(4) (BBO) was found to have huge birefringence in the 0.1-1.1 THz frequency region. Polarized terahertz transmission spectroscopy revealed a Delta n/n value of about 0.12 +/- 0.02. This result could be related to a polarization-dependent absorption that was observed at about 0.65 THz; in close agreement with first principles-calculations, showing this to be due to low-frequency phonon modes of the [B(3)O(6)](3)-rings. These findings suggest the utilization of the birefringent properties of BBO for optical parametric devices including amplifiers and oscillators, operating in the terahertz regime. (C) 2008 American Institute of Physics.