Vortex terahertz wave generation in air by femtosecond optical vortex pulses

摘要

This proceeding details the experimental investigation and scheme used to generate vortex beams at THz andfar-infrared frequencies. Main experimental and numrical results are presented by M. Ivanov et al. Weinvestigate the generation of broadband terahertz (THz) pulses between 10 and 40 THz with a phase singularityfrom two-color femtosecond laser-induced gas-plasmas. Experimental scheme allows for independent controlof the amplitude, phase, polarization, and longitudinal and transverse positions of fundamental and secondharmonics. When the second harmonic beam has a vortex charge the THz beam acquires an azimuthal phasemodulation as well. Moreover, it turns out that also the THz intensity becomes modulated along the azimuthalangle. The phase structure of the singular THz beam is indirectly revealed by astigmatic transformation of thebeam by a cylindrical mirror and additionally con rmed by the vortex THz beam behaviour upon change ofrelative phase between the fundamental and the second harmonic.