Dispersion calibration for the National Ignition Facility electron-positron-proton spectrometers for intense laser matter interactions.

Electron-positron pairs, produced in intense laser-solid interactions, are diagnosed using magnetic spectrometers with image plates, such as the National Ignition Facility Electron-Positron-Proton Spectrometers (EPPSs). Although modeling can help infer the quantitative value, the accuracy of the models needs to be verified to ensure measurement quality. The dispersion of low-energy electrons and positrons may be affected by fringe magnetic fields near the entrance of the EPPS.

Electron-Nanobunch-Width-Dominated Spectral Power Law for Relativistic Harmonic Generation from Ultrathin Foils.

Relativistic high-order harmonic generation from solid-density plasma offers a compact source of coherent ultraviolet and x-ray light. For solid targets much thinner than the laser wavelength, the plasma thickness can be tuned to increase conversion efficiency; a reduction in total charge allows for balancing the laser and plasma driving forces, producing the most effective interaction. Unlike for semi-infinite plasma surfaces, we find that for ultrathin foil targets the dominant factor in the emission spectral shape is the finite width of the electron nanobunches, leading to a power-law exponent of approximately 10/3.

The X-Ray Emission Effectiveness of Plasma Mirrors: Reexamining Power-Law Scaling for Relativistic High-Order Harmonic Generation.

Ultrashort pulsed lasers provide uniquely detailed access to the ultrafast dynamics of physical, chemical, and biological systems, but only a handful of wavelengths are directly produced by solid-state lasers, necessitating efficient high-power frequency conversion. Relativistic plasma mirrors generate broadband power-law spectra, that may span the gap between petawatt-class infrared laser facilities and x-ray free-electron lasers; despite substantial theoretical work the ultimate efficiency of this relativistic high-order-harmonic generation remains unclear. We show that the coherent radiation emitted by plasma mirrors follows a power-law distribution of energy over frequency with an exponent that, even in the ultrarelativistic limit, strongly depends on the ratio of laser intensity to plasma density and exceeds the frequently quoted value of  -8/3 over a wide range of parameters.

Laser Amplification in Strongly Magnetized Plasma.

We consider backscattering of laser pulses in strongly magnetized plasma mediated by kinetic magnetohydrodynamic waves. Magnetized low-frequency (MLF) scattering, which can occur when the external magnetic field is neither perpendicular nor parallel to the laser propagation direction, provides an instability growth rate higher than Raman scattering and a frequency downshift comparable to Brillouin scattering. In addition to the high growth rate, which allows smaller plasmas, and the 0.

Theory of electromagnetic wave frequency upconversion in dynamic media.

Frequency upconversion of an electromagnetic wave can occur in ionized plasma with decreasing electric permittivity and in split-ring resonator-structure metamaterials with decreasing magnetic permeability. We develop a general theory to describe the evolution of the wave frequency, amplitude, and energy density in homogeneous media with a temporally decreasing refractive index. We find that upconversion of the wave frequency is necessarily accompanied by partitioning of the wave energy into low-frequency modes, which sets an upper limit on the energy conversion efficiency.

X-ray amplification by stimulated Brillouin scattering.

Plasma-based parametric amplification using stimulated Brillouin scattering offers a route to coherent x-ray pulses orders of magnitude more intense than those of the brightest available sources. Brillouin amplification permits amplification of shorter wavelengths with lower pump intensities than Raman amplification, which Landau and collisional damping limit in the x-ray regime. Analytic predictions, numerical solutions of the three-wave-coupling equations, and particle-in-cell simulations suggest that Brillouin amplification in solid-density plasmas will allow compression of current x-ray free-electron laser pulses to subfemtosecond durations and unprecedented intensities.

Waveform-Controlled Relativistic High-Order-Harmonic Generation.

We consider the efficiency limit of relativistic high-order-harmonic emission from solid targets achievable with tailored light fields. Using one-dimensional particle-in-cell simulations, the maximum energy conversion efficiency is shown to reach as high as 10% for the harmonics in the range of 80-200 eV and is largely independent of laser intensity and plasma density. The waveforms most effective at driving harmonics have a broad spectrum with a lower-frequency limit set by the width of the incident pulse envelope and an upper limit set by the relativistic plasma frequency.

Strongly Enhanced Stimulated Brillouin Backscattering in an Electron-Positron Plasma.

Stimulated Brillouin backscattering of light is shown to be drastically enhanced in electron-positron plasmas, in contrast to the suppression of stimulated Raman scattering. A generalized theory of three-wave coupling between electromagnetic and plasma waves in two-species plasmas with arbitrary mass ratios, confirmed with a comprehensive set of particle-in-cell simulations, reveals violations of commonly held assumptions about the behavior of electron-positron plasmas. Specifically, in the electron-positron limit three-wave parametric interaction between light and the plasma acoustic wave can occur, and the acoustic wave phase velocity differs from its usually assumed value.

New diagnostic methods for laser plasma- and microwave-enhanced combustion.

The study of pulsed laser- and microwave-induced plasma interactions with atmospheric and higher pressure combusting gases requires rapid diagnostic methods that are capable of determining the mechanisms by which these interactions are taking place. New rapid diagnostics are presented here extending the capabilities of Rayleigh and Thomson scattering and resonance-enhanced multi-photon ionization (REMPI) detection and introducing femtosecond laser-induced velocity and temperature profile imaging. Spectrally filtered Rayleigh scattering provides a method for the planar imaging of temperature fields for constant pressure interactions and line imaging of velocity, temperature and density profiles.

Enhanced attosecond bursts of relativistic high-order harmonics driven by two-color fields.

We study the generation of attosecond x-ray and ultraviolet pulses from relativistically driven overdense plasma targets with two-color incident light. Particle-in-cell simulations show that significant improvement in pulse intensity and isolation is achievable with appropriate laser and plasma parameters. Conversion of 5% of incident laser energy to its second harmonic can enhance the intensity of generated attosecond pulses by an order of magnitude.

Analytical modeling and experimental characterization of chemotaxis in Serratia marcescens.

This paper presents a modeling and experimental framework to characterize the chemotaxis of Serratia marcescens (S. marcescens) relying on two-dimensional and three-dimensional tracking of individual bacteria. Previous studies mainly characterized bacterial chemotaxis based on population density analysis.

Magnetic steering control of multi-cellular bio-hybrid microswimmers.

Bio-hybrid devices, which integrate biological cells with synthetic components, have opened a new path in miniaturized systems with the potential to provide actuation and control for systems down to a few microns in size. Here, we address the challenge of remotely controlling bio-hybrid microswimmers propelled by multiple bacterial cells. These devices have been proposed as a viable method for targeted drug delivery but have also been shown to exhibit stochastic motion.

Influence of magnetic fields on magneto-aerotaxis.

The response of cells to changes in their physico-chemical micro-environment is essential to their survival. For example, bacterial magnetotaxis uses the Earth's magnetic field together with chemical sensing to help microorganisms move towards favoured habitats. The studies of such complex responses are lacking a method that permits the simultaneous mapping of the chemical environment and the response of the organisms, and the ability to generate a controlled physiological magnetic field.

Femtosecond laser electronic excitation tagging for quantitative velocity imaging in air.

Time-accurate velocity measurements in unseeded air are made by tagging nitrogen with a femtosecond-duration laser pulse and monitoring the displacement of the molecules with a time-delayed, fast-gated camera. Centimeter-long lines are written through the focal region of a ∼1 mJ, 810 nm laser and are produced by nonlinear excitation and dissociation of nitrogen. Negligible heating is associated with this interaction.

HMGB1 mediates endogenous TLR2 activation and brain tumor regression.

Background: Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor that carries a 5-y survival rate of 5%. Attempts at eliciting a clinically relevant anti-GBM immune response in brain tumor patients have met with limited success, which is due to brain immune privilege, tumor immune evasion, and a paucity of dendritic cells (DCs) within the central nervous system. Herein we uncovered a novel pathway for the activation of an effective anti-GBM immune response mediated by high-mobility-group box 1 (HMGB1), an alarmin protein released from dying tumor cells, which acts as an endogenous ligand for Toll-like receptor 2 (TLR2) signaling on bone marrow-derived GBM-infiltrating DCs.