Properties of the generation and propagation of spatiotemporal optical vortices

Abstract

Spatiotemporal optical vortex (STOV) light is a new type of vortex light with transverse orbital angular momentum (OAM) which is different from conventional spatial vortex light. Understanding the properties of STOV are meaningful before STOV are applied. We present a theoretical study on the generation and propagation of spatiotemporal vortices step by step based on diffraction theory. The properties of the output pulses with different topological charges generated using 4 f pulse shaper in both the near-field and the far-field are analyzed. Using spiral phase mask, the intensity profiles of the output pulses immediately after the 4 f pulse shaper are of multi-lobe structures. With energies circulating around the phase singularity in the space-time plane, energy coupling occurs between the spatial and temporal domains in the wave packets during propagation, then the intensity profiles evolve into multi-hole shapes, and the holes tend to be merged for higher order STOV. The conservation of OAM in the space-time domain is shown clearly. The profiles of the output pulses in the near-field form donut rectangle shapes using π-step mask, and in the far-field, they split into a multi-lobe structure. The rules of the generation and evolution of STOV are revealed. The results demonstrate the physical properties of the STOV and the generation and propagation processes directly and clearly. It provides a guidance on the application of STOV.

Propagation of transverse photonic orbital angular momentum through few-mode fiber

“…[21][22][23][24][25] STOV pulse has a spatiotemporally coupled field distribution. Under an unbalanced dispersion and diffraction phase, the STOV pulse can be significantly distorted, 15,16 leading to a breakup of the STOV charge and splitting the STOV pulse into multiple lobes in the spatiotemporal domain. This limits the use of the STOV pulse in many applications where a long interaction length and a tight confinement of the pulse are needed.…”

“…The STOV pulse, therefore, can carry a transverse photonic OAM of lℏ per photon 12 – 14 Since its discovery, much research has been done in studying STOV pulse, including studying its propagation dynamics, 15 , 16 developing novel characterization approaches, 17 – 19 utilizing STOV pulse in spatiotemporal imaging, 20 and designing other types of wave packets that also carry transverse photonic OAM 21 – 25 …”

Transverse orbital angular momentum of spatiotemporal optical vortices

“…We believe that experimental achievements go ahead of theoretical descriptions and understanding of these wave objects, and in some way, some properties of STOVs have been extrapolated from those of the purely spatial vortices in light beams. Detailed descriptions of the propagation features of STOVs can be found in [8][9][10], including closed-form expressions for higher-order STOVs (l > 1) propagating in free space [11]. Circularly symmetric, or given the different nature of the x and t coordinates, elliptically symmetric STOVs, are theoretically considered as prototype STOVs, and they are assumed to carry transverse OAM, but different authors provide expressions attributing different amounts of total, intrinsic, and extrinsic transverse OAM per photon [8,12,13], which has sparked a subtle debate [14].…”

The behavior of spatiotemporal Bessel-Gauss beams in atmospheric turbulence

“…[13][14][15][16][17][18][19][20][21] STOV-carrying light beams are now routinely generated in the laboratory, and researchers have started to contemplate possible applications, including optical communications, optical tweezing, and atomic optics. 6,10,11,22,23 While the free-space propagation behaviors of STOV-carrying light fields (and STC beams more generally) are generally understood, 6,[24][25][26] their behaviors in random media, such as atmospheric turbulence, have yet to be studied in detail. Two recent papers study how STC light beams behave in atmospheric turbulence, 27,28 but none, known to the author, examine STOV beams in particular.…”