arXiv subjects

Sida Cao

Publications and source records attributed to Sida Cao.

9 recordsLinked to original sources

arXiv2026

Gas Beam Dump and Power Meter for High Energy Lasers

Gaseous optics exhibit substantially higher laser-induced-damage thresholds than solid materials, enabling high-intensity operation without permanent degradation. In this Letter, we describe a gas-based beam dump and power meter that exploits the strong absorption of ozone in the Hartley band (200-320 nm). We develop and experimentally validate a model for ozone absorption that predicts the propagation length required for complete energy deposition and the resulting gas temperature rise. By calibrating the temperature rise against incident pulse energy, we demonstrate accurate millijoule-scale pulse energy measurements with an all-gas absorber. These results establish gas-phase absorbers as a scalable, debris-free platform for high-damage-threshold beam dumps and energy diagnostics for high-fluence lasers.

physics.optics↗

arXiv2026

Dispersive Properties of Plasma Diffraction Gratings: Towards Plasma-Based Laser Pulse Compression

The standard architecture for a high-peak-power femtosecond laser is chirped pulse amplification using diffraction gratings for compression; the damage threshold of the compression gratings limits current lasers to multi-petawatt peak power. Plasma gratings have orders-of-magnitude higher damage tolerance than conventional optics, so plasma gratings with sufficiently high optical quality could allow the construction of ultra-high-power femtosecond lasers. Here, we present experimental measurements of the angular dispersion, angular bandwidth, and diffraction angles of ionization-based plasma transmission gratings and show that both the dispersive and the diffractive properties of these gratings are in close agreement with optical theory and simulations. Gratings with a period of 10.2 microns are found to have an angular dispersion of approximately 0.005 degrees/nm. The dispersion and bandwidth of these gratings suggest plausible designs for a plasma-grating-based compressor and indicate a pathway to compact lasers with petawatt to exawatt peak power.

physics.plasm-ph↗

arXiv2026

Intense tunable terahertz radiation from phase-matched difference frequency generation in strongly magnetized plasmas

High-energy terahertz pulses are challenging to produce due to the low conversion efficiency and limited optical damage threshold of nonlinear crystals. Here, we describe the high-efficiency generation of terahertz radiation pulses with tunable frequency and field strengths exceeding 500 GV/m by propagating two-color laser pulses through a strongly magnetized plasma. The field strength is substantially enhanced by utilizing two extraordinary-mode branches to minimize the phase mismatch. We derive the phase-matching conditions and characterize the nonlinear coupling analytically, and validate these predictions with particle-in-cell simulations. These results establish a new pathway toward next-generation intense terahertz sources with performance well beyond the limits of existing plasma mechanisms and conventional crystal-based approaches.

physics.plasm-ph↗

arXiv2026

Near-Unity-Efficiency Gas Gratings for Ultraviolet, Visible, and Infrared High-Power Lasers

Interfering deep ultraviolet (DUV) lasers can induce substantial density modulations in an ozone-doped gas flow via photochemical reactions, creating volume diffraction gratings. These transient optics are immune to target debris and shrapnel and feature orders-of-magnitude higher damage thresholds than conventional solid optics, providing a promising method for efficiently manipulating high-energy lasers. In this work, we describe gas gratings that can efficiently diffract probe beams across a variety of wavelengths and pulse durations, ranging from deep ultraviolet to near-infrared and from nanosecond to femtosecond, achieving a full beam diffraction efficiency up to 99% while preserving the focusability and wavefront quality. In addition, we present a comprehensive characterization of the performance of the gas gratings under various experimental conditions, including imprint fluence, gas composition, and grating geometries, showing significant enhancement of this process with the addition of carbon dioxide. We also demonstrate stable performance over hours of operation. Our results validate a previously developed theoretical model and suggest optimal parameters to efficiently scale gas gratings to high-energy applications.

physics.optics↗

arXiv2025

Flying focus with arbitrary directionality for spatiotemporal control of laser pulses

Flying focus techniques produce laser pulses whose focal points travel at arbitrary, controllable velocities. While this flexibility can enhance a broad range of laser-based applications, existing techniques constrain the motion of the focal point to the propagation direction of the pulse. Here, we introduce a flying focus configuration that decouples the motion of the focus from the propagation direction. A chirped laser pulse focused and diffracted by a diffractive lens and grating creates a focal point that can move both along and transverse to the propagation direction. The focal length of the lens, grating period, and chirp can be tuned to control the direction and velocity of the focus. Simulations demonstrate this control for a holographic configuration suited to high-power pulses, in which two off-axis pump beams with different focal lengths encode the equivalent phase of a chromatic lens and grating in a gas or plasma. For low-power pulses, conventional solid-state or adaptive optics can be used instead. Multi-dimensional control over the focal trajectory enables new configurations for applications, including laser wakefield acceleration of ions, nonlinear Thomson scattering, and surface-plasmon emission of THz radiation.

physics.optics↗

arXiv2025

Focusing Terawatt-Scale Lasers Using Holographic Gaseous Lenses

The capabilities of the world's highest energy and peak-power pulsed lasers are limited by optical damage, and further advances in high-intensity laser science will require optics that are substantially more robust than existing components. We describe here the experimental demonstration of off-axis diffractive gaseous lenses capable of withstanding extreme laser fluence and immune to cumulative damage. We used less than 8 mJ of energy from interfering ultraviolet laser pulses to holographically write millimeter-scale diffractive gas lenses into an ozone, oxygen, and carbon-dioxide gas mixture. These lenses allowed us to focus, defocus, and collimate 532-nm, 210-mJ nanosecond laser pulses at fluences up to 35 J/cm$^2$ and 800-nm, 35-fs, 28-mJ femtosecond pulses at intensities up to 55 TW/cm$^2$, achieving greater than 80% diffraction efficiency. We also show that that beam pointing, divergence, and diffraction efficiency are stable while operating at 10 Hz. These diffractive lenses are simple holograms, and the principles demonstrated here extended to other types of optics suggests that gaseous optics could enable arbitrary, damage-resistant manipulation of intense light for next-generation ultra-high-power lasers.

physics.optics↗

arXiv2025

Electron penetration heating in turbulent magnetic loops driven by nonrelativistic laser-plasma interaction

Using particle-in-cell simulations to study nonrelativistic laser pulse propagation in a under-critical plasma, we identify a novel mechanism that occurs during the growth of turbulent magnetic loops: electron penetration heating. The loops have an electromagnetic left-hand chirality distinct from that of well-known quasistatic magnetic islands. The fast electrons penetrate through the loops and thus are accelerated to unexpected relativistic energies due to the symmetry breaking induced by the coupling between the loop field and the non-relativistic electromagnetic wave. The identified features of penetration heating and magnetic loops might provide an alternative perspective for understanding superponderomotive electron heating in under-critical plasmas irradiated by nonrelativistic laser pulses. This is a potential explanation for anomalous hot electron generation in scenarios of laser-driven inertial confinement fusion.

physics.plasm-ph↗

arXiv2024

High-energy transient gas pinholes via saturated absorption

This letter presents a spatial filter based on saturated absorption in gas as a replacement for the solid pinhole in a lens-pinhole-lens filtering system. We show that an ultraviolet laser pulse focused through ozone will have its spatial profile cleaned if its peak fluence rises above the ozone saturation fluence. Specifically, we demonstrate that a 5 ns 266 nm beam with 4.2 mJ of initial energy can be effectively cleaned by focusing through a 1.4% ozone-oxygen mixture, with about 76% of the main beam energy transmitted and 89% of the side lobe energy absorbed. This process can be adapted to other gases and laser wavelengths, providing alignment-insensitive and damage-resistant pinholes for high-repetition-rate high-energy lasers.

physics.optics↗

arXiv2024

Laser wakefield acceleration of ions with a transverse flying focus

The extreme electric fields created in high-intensity laser-plasma interactions could generate energetic ions far more compactly than traditional accelerators. Despite this promise, laser-plasma accelerators have remained stagnant at maximum ion energies of 100 MeV/nucleon for the last twenty years. The central challenge is the low charge-to-mass ratio of ions, which has precluded one of the most successful approaches used for electrons: laser wakefield acceleration. Here we show that a laser pulse with a focal spot that moves transverse to the laser propagation direction enables wakefield acceleration of ions to GeV energies in underdense plasma. Three-dimensional particle-in-cell simulations demonstrate that this relativistic-intensity "transverse flying focus" can trap ions in a comoving electrostatic pocket, producing a monoenergetic collimated ion beam. With a peak intensity of $10^{20}\,$W/cm$^2$ and an acceleration distance of $0.44\,$cm, we observe a proton beam with $23.1\,$pC charge, $1.6\,$GeV peak energy, and $3.7\,$% relative energy spread. This approach allows for compact high-repetition-rate production of high-energy ions, highlighting the capability of more generalized spatio-temporal pulse shaping to address open problems in plasma physics.

physics.plasm-ph↗