Characterization of birefringent material using polarization-controlled terahertz spectroscopy.

We present a polarization-controlled terahertz (THz) spectroscopy method to characterize the birefringent materials. The polarization of THz wave was controlled by changing the relative phase of the fundamental and second-harmonic waves in the two-color laser-induced air plasma THz generation configuration. The optical axis orientation was investigated through detecting one component of the transmitted THz electric field by continuously changing the electric field direction of the linearly polarized incident THz wave. This work demonstrates that the polarization-controlled THz spectroscopy can be used to study the anisotropy of the inner structure for birefringent materials.