Circularly polarized narrowband terahertz radiation from a eulytite oxide by a pair of femtosecond laser pulses

We report on terahertz radiation induced by an optical rectification process in a noncentrosymmetric and insulating oxide, eulytite Bi₄Ge₃O₁₂, at room temperature. The radiated terahertz pulse consists mainly of a temporal oscillation component with a frequency of 2.01 THz. The generation of this oscillation is ascribed to an increase in the effective generation length for the terahertz radiation up to about 2 mm at 2.01 THz. By using a pair of femtosecond laser pulses with an appropriate interval, polarization, and power, we succeeded in controlling the trajectory of the radiated terahertz wave. This method also enabled us to generate circularly polarized narrowband terahertz radiation with 2.01 THz.