This paper presents numerical simulations to study the heating of a solid target under a proton beam pulse interaction. The target is heated by the proton beam pulse with particle energy Eb, intensity N and focal radius rb of transverse Gaussian distribution, with a fixed pulse time 10 ps. The dynamics of target and beam ions are described by a classical hydrodynamic model and the target electrons are described by the quantum hydrodynamic model. Numerical simulations are carried out by employing the two dimensional flux-corrected transport methods. The target is heated to 0.5−5 eV, therefore, warm dense matter is created in the heated target region on a picosecond time scale.

Generation and evolution of plasma during femtosecond laser ablation of silicon are studied by steady-state and time-resolved spectroscopy in air, N2, SF6, and under vacuum. The plasma is generated faster than 200 ps (time resolution of our experiment) after excitation and mainly contains atoms and monovalent ions of silicon. Time-resolved spectra prove that silicon ions are faster than the silicon atoms which may be attributed to Coulomb repulsion and a local electric field when they are ejected from the silicon surface. During plasma evolution, ambient gas causes a confinement effect that enhances the dissociation of ambient gas molecules and the re-deposition of the removed material and leads to higher intensity and longer lifetime of the emission spectra. In SF6, a chemical reaction increases the plasma density and weakens the re-deposition effect. The different processes during plasma evolution strongly influence microstructure formation.

Electron plasma waves excited and/or modified by finite objects such as laser and charged particle pulses are investigated nonperturbatively using a simple model where the driver is unaffected by the interaction. It is shown that smooth as well as sharply peaked electron plasma wake waves of large amplitude can exist. In particular, two charged pulses moving in tandem can excite a highly localized electron plasma wave without producing the expected long wake wave, a configuration that should be particularly useful for efficient trapping and acceleration of electrons to high energies.

The application of laser accelerated ion beams in Hadron therapy requires ion beam optics with unique features. It has been shown that due to the spectral and spatial distribution of laser accelerated protons a lens based focusing system has advantages over aperture collimated beam formation. We present a compact ion optical system with therapy applications, based on Gabor space charge lenses for collecting, focusing and energy filtering the laser produced proton beam. For a full therapy solution, a scenario based on three space charge lenses is presented. In this very compact beam line an aperture is foreseen for energy selection.

A flyer with high velocity and good integrity can be obtained by laser driven multi-layered film. In order to deeply study the action mechanism, a calculation model of laser driven multi-layered flyer has been established, taking into account the effect of multi-layered on flyer velocity increase. Multi-layered flyer velocity driven by laser pulse beam has been calculated to decide film configuration capable of forming a high velocity flyer. Taking this film configuration as object, an intense laser driven multi-layered flyer experiment has been conducted to obtain flyer velocity and verify calculation model. In order to analyze flyer motion details, a two-dimensional axisymmetric computation model of laser driven flyer has been established. In this study, laser energy spatial-temporal distribution, film ablation, and plasma absorption laser to drive flyer have been considered. Saha ionization equilibrium equation is adopted to calculate film ionization degree and give plasma state equation. Dynamic mesh algorithm is used to calculate flyer motion. Coupled numerical simulation of laser ablation, laser interaction with plasma and plasma driven flyer has been achieved. Results show that flyer velocity firstly increases and then decreases with the increase of ablation layer thickness. Ablation layer has an optical laser absorption depth for different layer materials. Plasma velocity distribution is linear in axial when flyer accelerates. Insulation layer can decrease flyer temperature effectively to keep flyer integrity.

Surface periodic structures are generated upon irradiation of a silicon carbide (SiC) thin film by the plasma produced by 40 fs pulses from a Ti:Sapphire laser focused onto a thick low density polyethylene (LDPE) foil facing the SiC film. Independently of the number of laser pulses applied, these structures, with average regular periodicity of 710 nm, are evident throughout all irradiated areas. We attribute their formation to the efficient coupling of the unfocused femtosecond laser pulse with the incoherent extreme ultraviolet component of the laser-generated LDPE plasma.

The third harmonic generation of a self organized nonlinear laser Eigen mode of a two-dimensional plasma channel with complete electron evacuation from the inner region is investigated. The nonlinearities arise through the ponderomotive force and relativistic mass variations, while the ions are taken to be immobile. The second harmonic ponderomotive force produces electron density oscillations that beat with the oscillatory velocity due to the laser Eigen mode to create a nonlinear current, driving the third harmonic. As a0 increases up to the threshold value amin, at which complete electron evacuation begins in the inner region, the third harmonic amplitude rises rapidly. Above the threshold, as a0 increases, the width of the inner region where there is no third harmonic current, increases and third harmonic amplitude rises less rapidly. The conversion efficiency is found to be in reasonable agreement with the experimental results.

In this work, experiments were performed to study the effect of cathode materials on the amplitude of the super-short avalanche electron beam (SAEB) current and X-ray density during discharges in atmospheric-pressure air. In the experiments, discharges were generated by three nanosecond-pulse generators in air gaps between a plane anode and a tubular cathode made of different metals. The output pulse of the three generators had a rise time of 0.3, 1, 15 ns, and a full width at half maximum of 1, 2, 30–40 ns, respectively. For the generators with pulse rise-time of 0.3 and 1 ns, the cathodes used in these experiments were made of stainless steel, permalloy, titanium, niobium, copper, brass, and aluminum. For the generator with pulse rise-time of 15 ns, the cathodes were made of stainless steel, titanium, copper, and aluminum. When the rise time of the applied pulse is 0.3 ns, our experimental results show that the amplitude of the voltage across the gap depends on the cathode material and reaches its maximum value when a stainless steel cathode is used. It is also observed that, under such situation, the maximum amplitudes of the SAEB current occur at maximum voltages across the gap when all other factors are equal. Furthermore, the amplitude of the SAEB current hereof is found to depend not only on the material of the sharp edge of the tubular cathode, but also on the material of the side surface of the tubular cathode. When the rise time of the applied pulse is 1 ns, the experimental results show that the average number of electrons in SAEB is also affected by the cathode materials. In addition, in the case that the rise time of the voltage pulse is 15 ns and the gap spacing is 8 cm, the experimental results show that the cathode material has no effect on the voltage amplitude across the gap and the X-ray density. The increase of the pulse repetition frequency from 250 to 500 Hz under such condition can lead to a three-fold increase in X-ray density in a repetitive pulsed mode.

Lower hybrid wave excitation in magnetized plasma by an ion beam via Cerenkov interaction is studied. The lower hybrid modes showed maximum growth rate of the instability when phase velocity of the lower hybrid mode along the magnetic field is comparable to the electron thermal velocity. We have derived the expression for the maximum growth rate and found that the growth rate of the instability increases with beam density. Moreover, the maximum growth rate of the instability scales as the one-third power of the beam density. The real part of the frequency of the unstable wave increases as almost the square root of the beam energy.

The effect of smoothing by spectral dispersion (SSD) on stimulated rotational Raman scattering (SRRS) in air has been investigated both numerically and theoretically. The suppression effect of SSD on SRRS process is verified and it is demonstrated and proposed that the suppression effect is attributed to two aspects: the decreasing of the laser fluence modulation degree and the reducing of Stokes gain coefficient caused by the temporal and spatial variation of the phase of the incident laser pulse. The simulation results show that the SRRS threshold distance can be lengthened by choosing appropriate SSD parameters.

In the present paper, spatial amplitude modulation instability arising due to relativistic self-phase modulation and relativistic cross phase modulation of two co-propagating, linearly polarized laser beams (with arbitrary relative polarization) interacting with homogeneous plasma, has been studied. Wave equations including finite perturbation length effects, group velocity dispersion, and coupled nonlinear source term have been set up. Coupled dispersion relation for the two laser beams has been derived and solved numerically. The growth rate of modulation instability has been obtained and compared with the growth rate of a single beam propagating in homogeneous plasma. It has been shown that modulation instability of a single beam may either be enhanced or suppressed by co-propagation of another laser beam having appropriate polarization.

In this paper, a method of two-dimensional fine-scanning with charge coupled device has been conducted to precisely measure spatial position and intensity distribution of small-scale focal spot (diameter in microns). The measurement accuracy of the small-scale focal spot position is better than 1 µm when the fluctuations of the light energy and background noise are relatively small. The theoretical analysis is consistent with the experimental results.