arXiv subjects

M. S. Le

Publications and source records attributed to M. S. Le.

4 recordsLinked to original sources

arXiv2025

Spatiotemporal optical vortex (STOV) polariton

We confirm the existence of a new bulk medium quasiparticle with transverse orbital angular momentum (tOAM) and elucidate its physical origin. The tOAM structure is driven by torques induced by the ponderomotive force of the light in the medium, originating from the magnetic Lorentz force, even for weak light fields. There are two contributions to the material tOAM: one part depends on the pulse spatial shape change as it passes through an interface, and the other part depends on dispersion. The results, from first principles particle-in-cell simulations of a simple plasma, are in excellent agreement with our theory for general dielectric media [S. W. Hancock et al., Phys. Rev. Lett. 127, 193901 (2021)]. For plasma, there is agreement up to near-critical densities and near-relativistic field strengths.

physics.plasm-ph↗

arXiv2025

Transverse orbital angular momentum of amplitude-perturbed fields

We measure the change in transverse orbital angular momentum (tOAM) per photon, delta L_y, applied to an optical pulse by a pure amplitude perturbation. The results are in excellent agreement with calculations and simulations of the spatiotemporal torque based on our tOAM theory [Phys. Rev. Lett. 127, 193901 (2021)]. The crucial factor in determining delta L_y is the spatiotemporal distribution of tOAM density in the pulse. We show that even Gaussian pulses with zero total tOAM can have net tOAM induced by an amplitude perturbation stationary in the lab frame. As a prelude to the paper, we review and clarify several recent theoretical approaches to tOAM and reemphasize several fundamental principles needed for the correct analysis of experiments and simulations.

physics.optics↗

arXiv2024

Self-focused pulse propagation is mediated by spatiotemporal optical vortices

We show that the dynamics of high-intensity laser pulses undergoing self-focused propagation in a nonlinear medium can be understood in terms of the topological constraints imposed by the formation and evolution of spatiotemporal optical vortices (STOVs). STOVs are born from point phase defects on the sides of the pulse nucleated by spatiotemporal phase shear. These defects grow into closed loops of spatiotemporal vorticity that initially exclude the pulse propagation axis, but then reconnect to form a pair of toroidal vortex rings that wrap around it. STOVs constrain the intrapulse flow of electromagnetic energy, controlling the focusing-defocusing cycles and pulse splitting inherent to nonlinear pulse propagation. We illustrate this in two widely studied but very different regimes, relativistic self-focusing in plasma and non-relativistic self-focusing in gas, demonstrating that STOVs mediate nonlinear propagation irrespective of the detailed physics.

physics.optics↗

arXiv2023

Loss free shaping of few-cycle terawatt laser pulses

We demonstrate loss-free generation of 3 mJ, 1 kHz, few-cycle (5 fs at 750 nm central wavelength) double pulses with separation from 10 fs to 100 fs, using a helium filled hollow core fiber (HCF) and chirped mirror compressor. Crucial to our scheme are simulation-based modifications to the spectral phase and amplitude of the oscillator seed pulse to eliminate the deleterious effects of self-focusing and nonlinear phase pickup in the chirped pulse amplifier. The shortest pulse separations are enabled by spectral reshaping and pulse splitting in the HCF compressor.

physics.optics↗