Research progress on direct generation of ultrashort pulse OAM vortex beams (Invited)

Orbital angular momentum (OAM) vortex beam has a phase singularity with a twisted wave-front, whose complex amplitude comprises the helical term exp (ilθ). OAM vortex beam has been widely used in optical manipulation, imaging, optical communication, sensing and so on. Ultra-short pulse OAM vortex beams have the advantages of both vortex beams and ultra-short pulses, and can be applied to chiral material processing, long distance transmission, strong field physics and nonlinear frequency conversion. Direct generation of ultra-short OAM vortex beams has the advantages of compact and simple system and good beam quality. The research progress on direct generation of ultra-short OAM vortex beams was summarized. At present, the pulse width of the ultra-short OAM vortex beam generated by the active method is still limited to a few hundred femtoseconds. How to obtain the pulsed vortex beam output within 100 femtoseconds or even with a few cycles through the direct output method will be an important future development direction.