arXiv subjects

Titouan Gadeyne

Publications and source records attributed to Titouan Gadeyne.

6 recordsLinked to original sources

arXiv2026

Phase-locked beam splitting with continuously tunable intensity ratio using stochastic phase masks

We introduce a common-path beam splitter based on a randomly partitioned phase mask displayed on a spatial light modulator (SLM). The SLM aperture is divided into square patches, each randomly assigned to one of three phase ramps that steer light to three independent foci: two phase-locked beams and a dump that takes up the surplus power. We observe the beams in the focal plane of a lens. The fractions of patches assigned to each ramp set the focal intensities, with the focus positions controlled by the ramp slopes.We first demonstrate experimentally that the intensity ratio between the two foci can be tuned from 0 to 1 without distorting either of the spatial modes, and with their relative phase constant to within a few tens of mrad. We then derive a closed-form expression for the ensemble-averaged focal intensity, which decomposes into coherent foci of the desired pattern and a speckle background whose shape and amplitude are set by the patch size. The model is validated against experiment and against numerical Fraunhofer propagation, with quantitative agreement over about three orders of magnitude in intensity. We also identify the patch size as the central design parameter and characterize its experimental bounds.

physics.optics↗

arXiv2026

Near-focus intensity evolution of spatiotemporal optical vortex pulses and consequences for their nonlinear upconversion

Spatiotemporal optical vortex (STOV) laser pulses are attracting attention for their puzzling transverse orbital angular momentum (OAM) and propagation properties, which could determine their future applications. While the characteristic reshaping of their space-time envelope upon diffraction from the focal plane to the far-field is now well-established, the evolution of their intensity as they propagate has not been studied quantitatively, despite growing interest for their use in nonlinear optics and strong-field physics. Here, we explore experimentally and analytically the focusing dynamics of STOVs produced by a pulse shaper, and evidence a substantial longitudinal shift between the coordinate at which a circularly-symmetric STOV forms and that at which the pulse reaches its peak intensity. To illustrate some practical consequences for applications, we experimentally demonstrate how the yield of second-harmonic generation can consequently be maximized several Rayleigh lengths beyond the plane where the circular STOV really occurs. These results signal careful characterization of spatiotemporal pulses as a requisite for nonlinear optical experiments, and pave the way for finer control of complex laser drivers for light-matter interactions.

physics.optics↗

arXiv2026

Controlled generation of high-harmonic spatiotemporal optical vortices

Spatiotemporal optical vortex (STOV) pulses are puzzling states of light, which see their transverse orbital angular momentum being debated in spite of possessing a topological charge. Thus far studied at conventional optical wavelengths, we herein demonstrate their upconversion to extreme ultraviolet (XUV) frequencies via high-harmonic generation (HHG). Circularly-symmetric infrared STOV pulses of topological charges $\ell=\pm1$ and $\pm2$ from a bespoke pulse shaper are focused in argon to drive harmonics, each order $q$ forming a spatiospectral ring in the far-field. Dependence of their radii on $q$ and $\ell$ indicates XUV vortices of charge ${\ell}_{q} = q \times \ell$, and sensitivity of these modes to the focus position further establishes control over their production. The availability of XUV STOVs unlocks investigations and applications of their elusive angular momentum in the context of photoionization and other ultrafast spectroscopies.

physics.optics↗

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2025

Energy and photon centroids of spatiotemporal light pulses and consequences for their intrinsic orbital angular momentum

An ongoing debate surrounding the intrinsic transverse orbital angular momentum (OAM) attributed to spatiotemporal optical vortex (STOV) light pulses has raised the energy and photon-density centroids as two alternative frameworks to define the center of a free electromagnetic wavepacket. We herein derive, within a single formalism, lowest-order expressions for the positions and velocities of both centroids, directly applicable to an arbitrary scalar, near-paraxial and quasi-monochromatic pulse envelope formulated in space-time. Examining pulses with structures including temporal chirp, wavefront rotation, Gaussian-type STOVs and tilted lobulated profiles, we illustrate general principles underlying the shifts and propagation dynamics of the two centroids, and discuss how these properties underpin the value and conservation of intrinsic OAM referenced to either centroid. Finally, despite widespread use of the notion of intrinsic OAM "per photon", we argue that in neither framework could individual STOV photons be said to carry a well-defined quantum of intrinsic transverse OAM, as such quantities do not write as expectation values of a single operator for which STOV states could form a basis of orthogonal eigenmodes. This contrasts with the well-established quantization scheme for the total longitudinal OAM of light in spatial vortex beams, bearing implications for the interpretation of future experiments involving STOV pulses in quantum optics, nonlinear wave-mixing or light-matter interactions.

physics.optics↗

arXiv2024

Optical momentum distributions in monochromatic, isotropic random vector fields

We investigate the decomposition of the electromagnetic Poynting momentum density in three-dimensional random monochromatic fields into orbital and spin parts, using analytical and numerical methods. In sharp contrast with the paraxial case, the orbital and spin momenta in isotropic random fields are found to be identically distributed in magnitude, increasing the discrepancy between the Poynting and orbital pictures of energy flow. Spatial correlation functions reveal differences in the generic organization of different optical momenta in complex natural light fields, with the orbital current typically forming broad channels of unidirectional flow, and the spin current manifesting larger vorticity and changing direction over subwavelength distances. These results are extended to random fields with pure helicity, in relation to the inclusion of electric-magnetic democracy in the definition of optical momenta.

physics.optics↗