arXiv subjects

H. M. Milchberg

Publications and source records attributed to H. M. Milchberg.

At least 19 recordsLinked to original sources

arXiv2026

Optical air waveguides in strong turbulence

Filament-generated air waveguides offer a route to low loss long-distance optical transport, but their viability in atmospheric turbulence has remained uncertain. Here, we demonstrate with experiments and simulations that guided beams in air waveguides can overcome prior estimated turbulence limits by orders of magnitude in the refractive index structure parameter C_n^2; turbulent index fluctuations much larger than the waveguide index contrast average out along the propagation path. Instead, turbulence imposes two distinct limits: scattering of the guided field beyond the waveguide acceptance aperture and, more importantly at atmospheric strengths, scintillation of the waveguide-forming beam. Scaling of experimentally validated models indicates that filament-generated air waveguides remain viable over kilometer-scale paths under strong near-ground turbulence. Our results establish turbulence limits for long-range optical guiding in the atmosphere.

physics.optics↗

arXiv2026

RPC Telescope Tests for Muon Detection at Laser-Plasma Accelerators

We report on a feasibility study conducted at the ELBA facility at ELI Beamlines in 2025 to investigate the possible production of muons from high-energy electron beams generated by extended laser-plasma interactions in optically generated plasma waveguides. Our team operated a portable, autonomous, and compact telescope based on Resistive Plate Chamber (RPC) detectors, positioned to detect high-penetration charged particles originating from the beam dump. The campaign demonstrated that RPC detectors can operate reliably and safely in the ELBA environment, even under intense radiation and electromagnetic conditions. The collected datasets, though statistically limited and affected by lack of beam control, allow detailed characterization of the background and validated the detectors' stability and tracking performance. These results confirm the feasibility of the approach and provide the foundation for a dedicated future run under optimized beam conditions, where muon detection sensitivity will be substantially improved.

physics.ins-det↗

arXiv2026

Topologically constrained high intensity light propagation in air

We experimentally demonstrate how spatiotemporal optical vortices (STOVs) control long-range atmospheric filamentation of intense laser pulses. High-power pulses long enough to overlap with the delayed rotational nonlinearity of air molecules undergo periodic collapse arrest events, each of which generates toroidal STOV pairs with +/- topological charge that separate and accumulate into increasingly squeezed arrays of +1 charges at the front of the pulse and -1 charges at the back. These dynamics manifest as periodic energy deposition peaks along the propagation path and a pulse envelope modulated into a temporal intensity comb. Filamentation in this regime can be understood in terms of self-organized, topologically constrained defect dynamics embedded within nonlinear wave propagation.

physics.optics↗

arXiv2025

Plasma waveguides for high-intensity laser pulses

Fundamental to many applications of laser pulses in science and technology is an extended interaction length with matter that significantly exceeds the distance over which the pulse would normally diffract and transversely spread. At low intensity, the interaction could simply be the linear refraction provided by a glass optical fiber to keep the pulse from spreading. At increased pulse intensity, more than diffraction-free pulse transport is of interest: an extended interaction length of high intensity light can give rise to bright secondary sources of photons, and at relativistic intensities, beams of high energy charged particles. As generation of these secondary sources requires laser intensities well above the threshold for ionization of atoms, new methods for defeating pulse diffraction in a plasma have been developed. Chief among them are plasma waveguides: optical fibers composed of plasma that have characteristic mode structure. This article reviews the methods and theory of plasma waveguides, highlighting the recent development of meter-scale plasma waveguides that have been instrumental to the laser acceleration of high charge electron beams to ~10 GeV.

physics.plasm-ph↗

arXiv2025

Transverse orbital angular momentum: setting the record straight

The nature of the transverse orbital angular momentum (tOAM) associated with spatiotemporal optical vortex (STOV) pulses has been the subject of recent debate. We demonstrate that the approaches to tOAM presented in several recent papers are incorrect and lead to unphysical results, including erroneous claims of zero total tOAM. We emphasize the importance of calculating the OAM of any extended physical object at a common instant of time, and reemphasize the special status of the centre of energy as a reference point for all OAM calculations. The theory presented in [Phys. Rev. Lett. 127, 193901 (2021)] is the only correct classical field-based framework that both agrees with experiments and provides a self consistent understanding of transverse OAM in spatiotemporal light fields.

physics.optics↗

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

Excitation of Giant Surface Waves During Laser Wake Field Acceleration

We have detected the presence of very high intensity surface waves that are excited during plasma waveguided laser wakefield acceleration. Wakefield acceleration can be enchanced by the introduction of an ``all optical" plasma waveguide that confines and guides a laser pulse at the optimal intensity over long distances, producing quasimonoenergetic multi-GeV electron bunches. However strong pulses of radio frequency radiation (RF) are also produced, and particle in cell simulations show why: a continuous stream of multi-MeV electrons are also ejected radially from the plasma due to nonlinear wave breaking, and these excite and copropagate coherently with a giant cylindrical Sommerfeld surface wave. Laboratory measurements, simulations, and analytic approximations all converge on a 20 J laser pulse exciting a 1 Joule, 400 GW broadband THz surface wave, with a peak electric field strength of 35 GV/m.

physics.plasm-ph↗

arXiv2025

Longitudinal shaping of plasma waveguides using diffractive axicons for laser wakefield acceleration

New techniques for the optical generation of plasma waveguides -- optical fibres for ultra-intense light pulses -- have become vital to the advancement of multi-GeV laser wakefield acceleration. Here, we demonstrate the fabrication and characterization of a transmissive eight-level logarithmic diffractive axicon (LDA) for the generation of meter-scale plasma waveguides. These LDAs enable the formation of a Bessel-like beam with controllable start and end locations of the focal line and near-constant intensity on axis. We present measurements of the Bessel-like focal profile produced by the LDA, and of the leading end of the plasma column generated by it. One important feature is the formation of a funnel-mouthed plasma channel entrance that can act as waveguide coupler. We also compare the diffraction efficiency of our 8-level LDA to 4-level and binary versions, with measurements comparing well to theory.

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

Meter-scale supersonic gas jets for multi-GeV laser-plasma accelerators

Pushing the high energy frontier of laser wakefield electron acceleration (LWFA) to 10 GeV and beyond requires extending the propagation of relativistic intensity pulses to ~1 m in a low density ($N_e\sim 10^{17} cm^{-3}$) plasma waveguide. We present the development and characterization of two types of supersonic gas jet for meter-scale multi-GeV laser wakefield accelerators. The first type is a 30-cm long single-module gas jet, which demonstrates good axial uniformity using hydrogen, the preferred working gas for LWFA. The second type is a modular jet composed of multiple 11-cm-long modules. Longitudinal density profile control is demonstrated with a 2-module (22 cm long) hydrogen jet using gas valve trigger timing. A 1.0-m-long jet is then assembled from 9 modules, and generation of 1.0-m long hydrogen plasma is demonstrated using a femtosecond Bessel beam. To our knowledge, this is the longest gas jet laser plasma yet generated.

physics.acc-ph↗

arXiv2024

Remote detection of radioactive material using a short pulse CO2 laser

Detection of radioactive material at distances greater than the radiated particle range is an important goal with applications in areas such as national defense and disaster response. Here we demonstrate avalanche-breakdown-based remote detection of a 3.6 mCi alpha-particle source at a stand-off distance of 10 m, using 70 ps, long wave infrared (lambda=9.2 micron) CO2 laser pulses. This is ~10X longer than our previous results using a mid-IR laser. The primary detection method is direct backscatter from microplasmas generated in the laser focal volume. The backscatter signal is amplified as it propagates back through the CO2 laser chain, enhancing sensitivity by >100X. We also characterize breakdown plasmas with fluorescence imaging, and present a simple model to estimate backscattered signal as a function of the seed density profile in the laser focal volume. All of this was achieved with a relatively long drive laser focal geometry (f/200) that is readily scalable to >100 m.

physics.optics↗

arXiv2024

Matched Guiding and Controlled Injection in Dark-Current-Free, 10-GeV-Class, Channel-Guided Laser Plasma Accelerators

We measure the high intensity laser propagation throughout meter-scale, channel-guided LPAs by adjusting the length of the plasma channel on a shot-by-shot basis, showing high quality guiding of 500 TW laser pulses over 30 cm in a hydrogen plasma of density $n_0 \approx 1 \times 10^{17} \, \mathrm{cm^{-3}}$. We observed transverse energy transport of higher-order modes in the first $\approx 12 \, \mathrm{cm}$ of the plasma channel, followed by quasi-matched propagation, and the gradual, dark-current-free depletion of laser energy to the wakefield. We quantify the laser-to-wake transfer efficiency limitations of currently available PW-class laser systems, and demonstrate via simulation how control over the laser mode can significantly improve accelerated beam parameters. Using just 21.3 J of laser energy, and triggering localized electron injection into the accelerator, we observed electron bunches with single, quasimonoenergetic peaks, relative energy spreads as low as 3 % and energy up to 9.2 GeV with charge extending beyond 10 GeV.

physics.plasm-ph↗

arXiv2024

Benchmarking of hydrodynamic plasma waveguides for multi-GeV laser-driven electron acceleration

Hydrodynamic plasma waveguides initiated by optical field ionization (OFI) have recently become a key component of multi-GeV laser wakefield accelerators. Here, we present the most complete and accurate experimental and simulation-based characterization to date, applicable both to current multi-GeV experiments and future 100 GeV-scale laser plasma accelerators. Crucial to the simulations is the correct modeling of intense Bessel beam interaction with meter-scale gas targets, the results of which are used as initial conditions for hydrodynamic simulations. The simulations are in good agreement with our experiments measuring evolving plasma and neutral hydrogen density profiles using two-color short pulse interferometry, enabling realistic determination of the guided mode structure for application to laser-driven plasma accelerator design.

physics.plasm-ph↗

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↗

arXiv2023

Guided mode evolution and ionization injection in meter-scale multi-GeV laser wakefield accelerators

We show that laser wakefield electron accelerators in meter-scale, low density hydrodynamic plasma waveguides operate in a new nonlinear propagation regime where sustained beating of lowest order modes of the ponderomotively modified channel plays a significant role, whether or not the injected pulse is linearly matched to the guide. For a continuously doped gas jet, this mode beating effect leads to ionization injection and a striated multi-GeV energy spectrum of multiple quasi-monoenergetic peaks; the same process in a locally doped jet produces single multi-GeV peaks with <10% energy spread. A 3-stage model of drive laser pulse evolution and ionization injection characterizes the beating effect and explains our experimental results.

physics.plasm-ph↗

arXiv2023

Spatiotemporal torquing of light

We demonstrate the controlled spatiotemporal transfer of transverse orbital angular momentum (OAM) to electromagnetic waves: the spatiotemporal torquing of light. This is a radically different situation than OAM transfer to longitudinal, spatially-defined OAM light by stationary or slowly varying refractive index structures such as phase plates or air turbulence. We show that transverse OAM can be imparted to a short light pulse only for (1) sufficiently fast transient phase perturbations overlapped with the pulse in spacetime, or (2) energy removal from a pulse that already has transverse OAM. Our OAM theory for spatiotemporal optical vortex (STOV) pulses [Phys. Rev. Lett. 127, 193901 (2021)] correctly quantifies the light-matter interaction of this experiment, and provides a torque-based explanation for the first measurement of STOVs [Phys. Rev. X 6, 031037 (2016)].

physics.optics↗

arXiv2023

Quasi-steady-state air waveguide

We report the first generation of quasi-steady-state air waveguides capable of guiding high average power laser beams. The guides are produced by high-repetition rate patterned filamentation of femtosecond laser pulses. We demonstrate near-continuous guiding of a CW probe beam with significantly higher efficiency than transient guides at lower repetition rates.

physics.optics↗