13:30 〜 13:45
▼ [19p-H116-2] Generation of third-harmonic vortex beams by near-infrared femtosecond laser pulse filamentation in air
キーワード：optical vortex,filamentation,third-harmonic generation
To the best of our knowledge, we present the first observation on third-harmonic (TH) generation of vortex beams in air during the filamentation of intense femtosecond pulses generated by a lab-built Ti:sapphire chirped pulse amplifier. The TH beam profile shows a vortex ring at lower pump energy and is then surrounded by another vortex ring due to the TH conical emission at higher pump energy. We validate that each TH vortex ring follows the conservation of the orbital angular momentum (OAM). It is shown that each TH vortex ring possesses the OAM three times larger than the fundamental one. We further investigate the evolution of spatially resolved spectra for the TH waves and find that the vortex rings in the TH wave reveal distinct phenomena. At lower pump energy, the phase-matching between the fundamental and TH waves dominates the nonlinear optical effect of both the vortex rings, whereas at higher pump energy, the dispersion properties of air begin to affect the spectrum of the inner vortex ring, leading to the formation of spectrum broadening.