Powerful laser-produced quasi-half-cycle THz pulses.

The Maxwell equations-based 3D-analytical solution for the terahertz (THz) half-cycle electromagnetic wave transition radiation pulse has been found. This solution describes generation and propagation of transition radiation into free space from laser-produced relativistic electron bunch which crosses a target-vacuum interface as a result of ultrashort laser pulse interaction with a thin high-conductivity target. The analytical solution found complements the theory of laser initiated transition radiation.

Ultrafast target charging due to polarization triggered by laser-accelerated electrons.

A significant step has been made towards understanding the physics of the transient surface current triggered by ejected electrons during the interaction of a short intense laser pulse with a high-conductivity target. Unlike the commonly discussed hypothesis of neutralization current generation as a result of the fast loss of hot electrons to the vacuum, the proposed mechanism is associated with excitation of the fast current by electric polarization due to transition radiation triggered by ejected electrons. We present a corresponding theoretical model and compare it with two simulation models using the finite-difference time-domain and particle-in-cell methods.

Ion energy spectra directly measured in the interaction volume of intense laser pulses with clustered plasma.

The use of gas cluster media as a target for an intense femtosecond laser pulses is considered to be uniquely convenient approach for the development of a compact versatile pulsed source of ionizing radiation. Also, one may consider cluster media as a nanolab to investigate fundamental issues of intense optical fields interaction with sub-wavelength scale structures. However, conventional diagnostic methods fail to register highly charged ion states from a cluster plasma because of strong recombination in the ambient gas.

Electrostatic fluctuations in collisional plasmas.

We present a theory of electrostatic fluctuations in two-component plasmas where electrons and ions are described by Maxwellian distribution functions at unequal temperatures. Based on the exact solution of the Landau kinetic equation, that includes electron-electron, electron-ion, and ion-ion collision integrals, the dynamic form factor, S(k[over ⃗],ω), is derived for weakly coupled plasmas. The collective plasma responses at ion-acoustic, Langmuir, and entropy mode resonances are described for arbitrary wave numbers and frequencies in the entire range of plasma collisionality.

Synchronized Ion Acceleration by Ultraintense Slow Light.

An effective scheme of synchronized laser-triggered ion acceleration and the corresponding theoretical model are proposed for a slow light pulse of relativistic intensity, which penetrates into a near-critical-density plasma, strongly slows, and then increases its group velocity during propagation within a target. The 3D particle-in-cell simulations confirm this concept for proton acceleration by a femtosecond petawatt-class laser pulse experiencing relativistic self-focusing, quantify the characteristics of the generated protons, and demonstrate a significant increase of their energy compared with the proton energy generated from optimized ultrathin solid dense foils.

Electrostatic response of a two-component plasma with Coulomb collisions.

A rigorous procedure is proposed for finding a solution to kinetic equations with the Landau electron-electron, electron-ion, ion-electron, and ion-ion collision integrals in fully ionized plasma. The linear plasma response to the perturbation in the electrostatic field is described in terms of plasma dielectric permittivity. Solutions of the dispersion relation for electron plasma waves, ion-acoustic waves, and entropy modes are found in the entire range of frequencies, wave vectors, and particle collisionality.

Ion response to relativistic electron bunches in the blowout regime of laser-plasma accelerators.

The ion response to relativistic electron bunches in the so called bubble or blowout regime of a laser-plasma accelerator is discussed. In response to the strong fields of the accelerated electrons the ions form a central filament along the laser axis that can be compressed to densities 2 orders of magnitude higher than the initial particle density. A theory of the filament formation and a model of ion self-compression are proposed.

Accelerating monoenergetic protons from ultrathin foils by flat-top laser pulses in the directed-Coulomb-explosion regime.

We consider the effect of laser beam shaping on proton acceleration in the interaction of a tightly focused pulse with ultrathin double-layer solid targets in the regime of directed Coulomb explosion. In this regime, the heavy ions of the front layer are forced by the laser to expand predominantly in the direction of the pulse propagation, forming a moving longitudinal charge separation electric field, thus increasing the effectiveness of acceleration of second-layer protons. The utilization of beam shaping, namely, the use of flat-top beams, leads to more efficient proton acceleration due to the increase of the longitudinal field.

Accelerating protons to therapeutic energies with ultraintense, ultraclean, and ultrashort laser pulses.

Proton acceleration by high-intensity laser pulses from ultrathin foils for hadron therapy is discussed. With the improvement of the laser intensity contrast ratio to 10(-1) achieved on the Hercules laser at the University of Michigan, it became possible to attain laser-solid interactions at intensities up to 10(22) W/cm2 that allows an efficient regime of laser-driven ion acceleration from submicron foils. Particle-in-cell (PIC) computer simulations of proton acceleration in the directed Coulomb explosion regime from ultrathin double-layer (heavy ions/light ions) foils of different thicknesses were performed under the anticipated experimental conditions for the Hercules laser with pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half maximum (FWHM), focused to a spot size of 0.

Kinetic susceptibility and transport theory of collisional plasmas.

A system of nonlocal electron transport equations for electrostatic perturbations in (omega,k) space in a high-Z plasma is derived from the Fokker-Planck equation for arbitrary relations between the time, space, and collisionality scales. The closed scheme for obtaining the longitudinal plasma susceptibility epsilon(omega,k) in the entire (omega,k) plane is proposed. Regions in the (omega,k) plane have been mapped for problems such as the relaxation of the local temperature enhancement with a time-dependent heat conductivity.

Effect of nonlocal transport on heat-wave propagation.

We present the first direct measurements of spatially and temporally resolved temperature and density profiles produced by nonlocal transport in a laser plasma. Absolutely calibrated measurements have been performed by Rayleigh scattering and by resolving the ion-acoustic wave spectra across the plasma volume with Thomson scattering. We find that the electron temperature and density profiles disagree with flux-limited models, but are consistent with nonlocal transport modeling.

Anomalous absorption of high-energy green laser light in high- z plasmas.

We observe strong anomalous absorption of green laser light in mm-scale high-temperature gold plasmas. Both the laser light absorption and the resulting increase of the electron temperature, which was measured independently with Thomson scattering, have been successfully modeled by including enhanced collisions due to heat-flux driven ion acoustic fluctuations. Calculations that include only inverse bremsstrahlung significantly underestimate the experimental laser absorption and the electron temperature.