AMBIENT AIR USED AS THE NONLINEAR MEDIA FOR THZ WAVE GENERATION

We report the first systematic study of broadband THz wave generation with ambient air as the nonlinear media. Generation of pulsed THz waves with mixing the fundamental and the second harmonic beams in air has been previously demonstrated by Cook et al. and Hartmut et al. while different groups obtained different results. To verify the proposed mechanism of strong THz wave generation, we measured dependence of generated THz field on the polarization, amplitude and phase of the individually controlled two beams. Our results confirm that four-wave-mixing rectification is the major mechanism this phenomenon, and the amplitude and polarity of generated THz wave can be controlled by the relative phase of the beams. This work is significant by providing the feasibility of THz wave generation and detection with a standoff distance greater than 50 meters.