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Register a new userGeneration of spatiotemporal optical vortices with partial temporal coherence
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Recently, a spatiotemporal optical vortex (STOV) with a transverse orbital angular momentum (OAM) has been generated from coherent ultrafast pulses using mode-locked lasers. In contrast, we demonstrate theoretically and experimentally that a STOV can be generated from a light source with partial temporal coherence with fluctuating temporal phase. By eliminating the need of mode-locked laser sources, the partially coherent STOV will serve as a convenient and cost-effective transverse OAM source.
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Recently, photons have been observed to possess transverse orbital angular momentum (OAM); however, it is unclear as whether they can hold a transverse OAM higher than 1. Here, we theoretically and experimentally demonstrate that high-order spatiotemporal Bessel optical vortices (STBOVs) can stably carry transverse OAM even beyond $10^2$. Through the inverse design of the spiral phase, an STBOV of any order can be controllably generated using a 4f pulse shaper. In contrast to conventional longitudinal OAM, the vector direction of the transverse OAM can be distinguished by the unique time-symmetrical evolution of STBOVs. More interestingly, the stability of STBOVs improves with their increasing orders owing to enhanced space-time coupling, making these beams particularly suitable for the generation of ultra-high transverse OAM. Our work paves the way for further research and application of this unique OAM of photons.
We describe an experimental technique to generate a quasi-monochromatic field with any arbitrary spatial coherence properties that can be described by the cross-spectral density function, $W(mathbf{r_1,r_2})$. This is done by using a dynamic binary amplitude grating generated by a digital micromirror device (DMD) to rapidly alternate between a set of coherent fields, creating an incoherent mix of modes that represent the coherent mode decomposition of the desired $W(mathbf{r_1,r_2})$. This method was then demonstrated experimentally by interfering two plane waves and then spatially varying the coherent between these two modes such that the interference fringe visibility was shown to vary spatially between the two beams in an arbitrary and prescribed way.
As a new degree of freedom for optical manipulation, recently spatiotemporal optical vortices (STOVs) carrying transverse orbital angular momentums have been experimentally demonstrated with bulky optical systems. Here we propose a spatiotemporal differentiator to generate STOVs with pure transverse orbital angular momentum. In order to create phase singularity in the spatiotemporal domain, we design a spatiotemporal differentiator by breaking spatial mirror symmetry. In contrast to the complex bulky systems, the device we propose here is a simple one-dimensional periodic nanostructure and thus it is much more compact. We show that for a normal incident pulse, the differentiator generates a transmitted STOV pulse with transverse orbital angular momentum. Furthermore, we demonstrate that the interference of the generated STOVs can be used to detect the sharp changes of pulse envelopes, in both spatial and temporal dimensions.
We introduce a model for spatiotemporal modelocking in multimode fiber lasers, which is based on the (3+1)-dimensional cubic-quintic complex Ginzburg-Landau equation (cGLE) with conservative and dissipative nonlinearities and a 2-dimensional transverse trapping potential. Systematic numerical analysis reveals a variety of stable nonlinear modes, including stable fundamental solitons and breathers, as well as solitary vortices with winding number $n=1$, while vortices with $n=2$ are unstable, splitting into persistently rotating bound states of two unitary vortices. A characteristic feature of the system is bistability between the fundamental and vortex spatiotemporal solitons.
We experimentally generate cylindrically polarized wavepackets with transverse orbital angular momentum, demonstrating the coexistence of spatiotemporal optical vortex with spatial polarization singularity. The results in this paper extend the study of spatiotemporal wavepackets to a broader scope, paving the way for its applications in various areas such as light-matter interaction, optical tweezers, spatiotemporal spin-orbit angular momentum coupling, etc.
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