Non-spreading Bessel spatiotemporal optical vortices

Time diffraction-free transverse orbital angular momentum beams

“…However, due to the similar issue of modulation method, these beams lack experimental observation so far. We note that a strategy to synthesize STB vortices via superimposing a spiral phase with a conical phase has been proposed very recently 19 . Still, due to its reliance on time-delayed modulation, obvious separation of topological charges even for l = 2 has been observed.…”

“…Particularly, such degradation leads to instability of integral OAM value 16 , limiting greatly the scientific research for and the real-world application of transverse OAM. Till now, most experimental efforts attributed this mode degradation to ST astigmatism effect, i.e., the mismatch between spatial diffraction and medium dispersion 14 , 16 , 19 . In contrast, a few theoretical studies introduced a novel effect—termed time diffraction—via a plane-wave expansion method, providing a new perspective to investigate ST vortices and their degradation 11 , 17 .…”

Quadrics for Structuring Invariant Space–Time Wavepackets

“…11 Besides the intense research activities on optical vortex beams carrying longitudinal OAM (i.e., the spiral phase twists in the spatial domain), the recent studies on spatiotemporal optical vortices (STOVs) carrying transverse or tilted OAM (here the phase rotates in the spatiotemporal domain) have opened up new opportunities for structuring light. [12][13][14][15][16][17] More generally, structured light, particle beams, and invariant wavepackets are nowadays indispensable tools in numerous fields of science and technology, [18][19][20][21][22][23][24] and a new step forward in the advanced control of wave propagation would facilitate the emergence of new functionalities. While most of the above examples have been deeply studied in the monochromatic regime, strong interest is currently shown for space-time (ST) invariant wavepackets.…”

“…[27][28][29] Invariant STOVs have also been observed in the anomalous dispersion regime. 16 Structuring the space-time characteristics of a field turns out to be a very versatile way to engineer the pulse propagation dynamics, allowing, for instance, to control the group velocity 25,30 or group velocity dispersion, [31][32] as well as OAM features 16,33 of the structured wavepackets. Not only used for sculpting "at will" the propagation dynamics, the framework of invariant ST wavepackets has provided a deeper understanding of the mechanisms responsible for supercontinua generation during the nonlinear propagation of ultrashort pulses.…”

“…Every invariant ST wavepackets studied so far could be investigated within a similar framework. Note that the same analysis could be performed in spherical coordinates 37 or space-time cylindrical coordinates, 16 the quest for invariant wavepackets being intertwined with symmetries of the considered medium of propagation.…”