In the paper, we applied the paraxial region theory and Wentzel–-Kramers–-Brillouin approximation to study laser beam self-focusing in the interaction of laser and collisional plasma with periodical density ripple. The results have shown that, under the influence of collision nonlinear effect, laser presents stable self-focusing, self-defocusing, and oscillational self-focusing in the plasma. Besides, the parameters of plasma with periodical density ripple have a greater impact on the effect of self-defocusing and oscillational self-focusing than stable self-focusing. In certain conditions, beam self-defocusing and oscillational self-focusing would decline and even disappear, and stable self-focusing would further be strengthened. Hence, selecting a suitable periodic plasma system is advantageous for separating self-defocusing and oscillational self-focusing, and for the formation of a more stable collisional self-focusing.

The relativistic mirror (RM) is an interesting subject which introduced in the nonlinear regime of the laser–plasma interaction. Reflection of counter-propagating probe pulse from relativistic flying mirror has some excellent features, such as frequency up-shifting and compressing by a factor of 4γ2. In the high-intensity laser–plasma interaction, sometimes a sequence of RMs creates. For example, electron density cusps generate in the nonlinear laser wakefield generation or flying electron sheaths create in the blown-out regime of the laser foil interaction. Under these circumstances, the second counter-propagated seed (probe) pulse can be reflected back and forth between two or more successive RMs. This structure may be used as a relativistic cavity (RECA). Amplification and threshold conditions for the gain medium and pumping rate in the RECA are obtained, and it is shown that amplification can be started from background simultaneous emission (without seed pulse). A new feature of RECA is it's bidirectional (two frequencies) characteristic. Thereupon, the gain process can be implemented on the two different transitions in this bidirectional gain structure. In the RECA, driver pulse may be assembled as a pumping operation, and background plasma medium with high degree ionized substances is a good candidate for gain medium in the UV or X-ray regions. In this paper, we propose a new all-optical cavity for the generation of the ultrashort laser pulse in the UV or X-ray regions.

In a collisionless shock, there are no binary collisions to isotropize the flow. It is therefore reasonable to ask to which extent the magnetohydrodynamics (MHD) jump conditions apply. Following up on recent works which found a significant departure from MHD in the case of parallel collisionless shocks, we here present a model allowing to compute the density jump for collisionless shocks. Because the departure from MHD eventually stems from a sustained downstream anisotropy that the Vlasov equation alone cannot specify, we hypothesize a kinetic history for the plasma, as it crosses the shock front. For simplicity, we deal with non-relativistic pair plasmas. We treat the cases of parallel and perpendicular shocks. Non-MHD behavior is more pronounced for the parallel case where, according to MHD, the field should not affect the shock at all.

In this paper, self-focusing of finite Airy–Gaussian (AiG) laser beams in collisionless plasma has been investigated. The source of nonlinearity considered herein is relativistic. Based on the Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations, the nonlinear coupled differential equations for beam-width parameters in transverse dimensions of AiG beams have been established. The effect of beam's modulation parameter and linear absorption coefficient on the self-focusing/defocusing of the beams is specifically considered. It is found that self-focusing/defocusing of finite AiG beams depends on the range of modulation parameter. The extent of self-focusing is found to decrease with increase in absorption.

In this article, Si nanoparticle (NP) films were prepared by pulsed laser ablation (PLA) in the argon atmosphere of 10 Pa at room temperature under different pulse repetition rates from 1 to 40 Hz without the baffle. Different from the conventional PLA method, the substrates were placed below and parallel to the ablated plume axis. The obtained films containing NPs were characterized by scanning electron microscopy and Raman spectrometer. The experimental results under constant laser fluence demonstrate the strong dependence of the mean size and the area number density of NPs on the repetition rate. Specifically, with the increase of pulse repetition rate, the mean size of the NPs in the film first decreases and reaches its minimum at 20 Hz, and then increases after 20 Hz, and decreases again till 40 Hz. The area number density shows the contrary trend versus mean size. The in situ diagnostic results of Langmuir probe denote the ablated Si ion density increases monotonously with the increase of repetition rate, while the temperature is almost constant. Combining with the nucleation probability, the growth/aggregation duration of NPs in the “nucleation region” and the effect of the baffle, the influence of pulse repetition rate on the formation of NPs is addressed. It is found that the repetition rate impacts the growth modes of NPs (i.e., growth and aggregation). 1–20, 20–30, and 30–40 Hz, respectively, correspond to growth-, aggregation-, and growth-controlled rate ranges without the baffle; however, 1–10, 10–20, and 20–40 Hz, respectively, correspond to growth-controlled, aggregation/growth-coexisted, and aggregation-controlled rate ranges with the baffle.

We present an accurate approach of the basic ultra-relativistic effects which occur at the interactions between laser beams and electrons and correspond to laser beam intensities greater than 1020 W/cm2. These effects are the generation of extremely bright pulses and the existence of a very large frequency spectrum of the radiation generated by this interaction, containing relative intense harmonics of orders higher than 800. Our results are in good agreement with the experimental results published in the literature.

We present a theory for describing the inner structure of the electron bunch in the bubble regime starting from a random distribution of electrons inside the bubble and subsequently minimizing the system's energy. Consequently, we find a filament-like structure in the direction of propagation that is surrounded by various shells consisting of further electrons. If we specify a two-dimensional (2D) initial structure, we observe a hexagonal structure for a high number of particles, corresponding to the close packing of spheres in two dimensions. The 2D structures are in agreement with the equilibrium slice model.

A recently published scheme for inertial fusion based on instantaneous heating of an uncompressed fuel is criticized. It is shown that efficient fusion and “time-like” fusion burn propagation cannot be realized due to the low nuclear reaction cross-sections. The suggested use of nanospheres inside the volume of the target to support the fast heating of the fuel is also questioned.

In this study, we have spectroscopically investigated the plasma generated by a Q-switched Nd:YAG laser operating at its fundamental wavelength of 1064 nm focused on magnesium (Mg) and titanium (Ti) target samples in the air under atmospheric pressure. We employed circular cavities of radii (2.5, 3.0, and 3.5 mm) and a square cavity to investigate the cavity confinement effect on the spectral emission intensities of the plasmas. We observed that the circular cavity of radius 2.5 mm had the maximum signal enhancement, and this can be attributed to the compression of the plasma and reheating by the reflected shock waves. The maximum enhancement factor of the Mg I-518.4 nm line was reached at approximately 3.8, 3.4, and 2.8 with a circular cavity of radius 2.5, 3.0, and 3.5 mm, respectively, at a delay time of 350 ns and a laser energy of 350 mJ. By applying varying external magnetic fields (0.47, 0.62, 0.91, and 1.23 T) across the generated plasma, the plasma parameters such as electron temperature and number density have been investigated. From our results, we observed that the radius of the cavity had a tremendous effect on the enhancement of the emission signal intensities. We also found that the increase in the electron temperature and the number density can be attributed to the increase in the applied magnetic field and the laser energy. From our calculations, the value of β, which was less than 1 for all the cases, confirms that there was a plasma confinement at the presence of the magnetic field.

In the present work, Titanium dioxide (TiO2) micro–nanostructured thin films are deposited by a cold atmospheric plasma jet on carbon fiber substrates. The surface morphology, grain size, and structure phase of TiO2 thin films are investigated by scanning electron microscopic (SEM), X-ray diffraction (XRD), and Raman spectrum. As the discharge voltage increased from 5 to 15 kV, the size of these TiO2 particles decreased from 2 to 3 μm to less than 1 μm. The XRD and Raman spectroscopic results show TiO2 on the carbon fiber surface prepared by atmospheric plasma jet is at the mixture phase of anatase and rutile. We also investigated the adhesion and proliferation assays of MC3T3-E1 preosteoblasts on the samples. The surface with smaller TiO2 particles deposited on carbon fiber is more appropriate for attachment of preosteoblasts. Furthermore, the highest proliferation of MC3T3-E1 was found on a sample with smaller TiO2 particles after incubation. Our data suggest that the increased roughness fosters cell attachment and proliferation on the surface of TiO2/carbon fibers.

In this paper, we characterize a high repetition-rate regenerating plasma mirror produced by the thin film of liquid formed when two laminar streams collide. The use of a flowing liquid film is inexpensive and the interaction surface refreshes automatically, avoiding buildup of on-target debris. The composition of the liquid material and the relative angle of the film-generating nozzles was optimized for this application. Spectra measured in reflection from a water-based plasma mirror showed a blue shift but an optical reflectivity of up to 30%. The thickness of the film was found to be of the order of 2 ${\rm \mu}$m, and the stability of the reflected spot was ${\approx }1$ mrad. The reflected beam profile was highly distorted but stable. Further optimization of the nozzles to affect the fluid flow should enable significant improvements in control of the fluid films and increase in the reflectivity of these mirrors.

The ab initio molecular dynamics (MD) simulations using an atom-centered density matrix propagation method are carried out in the first time to investigate the dissociative electron attachment (DEA) processes of adenine and its tautomer in the gas phase. Since the incoming electron are captured on the lowest π∗ anti-bond orbital, which is led to the different N–H bond, the C–H bond and the C–N bond are broken. The dominant anion observed in DEA dissociation process is the closed-shell dehydrogenated anion (Ade − H)−. The additional anions (Ade − NH2)− and (Ade − 2H)− are also obtained in ADMP simulation. The results are well consistent with the previous DEA experimental results. Thus, the ADMP method is used to gain a more intuitive and better understanding of the necessary dissociation process in the DEA experiment.

For the guarantee of the long-distance transport of the bunches of China Initiative Accelerator Driven System (CIADS), a new scheme is proposed that extra magnetic field is used in the accelerator-target coupling section before the windowless target to minimize the self-modulation (SM) mechanism. Particle-in-cell simulations are carried out to study the influence of the solenoidal magnetic field on the self-modulation mechanism when long proton bunches move in the background plasmas. The long proton bunches used in the simulations are similar to these in the linear accelerator of CIADS. It is found that the presence of the solenoidal magnetic field will significantly inhibit the self-modulation process. For the strong magnetic field, the longitudinal separation and transverse focusing of the long bunches disappear. We attribute these phenomena to the reason that the strong solenoidal magnetic field restricts the transverse movement of plasma electrons. Thus, there are not enough electrons around the bunch to compensate the space charge effect. Moreover, without transverse current, the longitudinal pinched effect disappears, and the long bunch can not be separated into small pulses anymore.

Increasing the output power of a long-wavelength free-electron laser (FEL), despite the destroying effects of beam energy spread, is studied using the optimal pre-bunching of the thermal electron beam along with the optimal tapering of the planar wiggler magnetic field. A set of self-consistent coupled nonlinear differential equations in three dimensional that describe the evolution of radiation and electron beam in the interaction zone are solved numerically by the Runge–Kutta method. The axial energy spread is considered and it degrades the FEL performance by reducing the saturation power and increasing the saturation length. To compensate these destroying effects, the optimum function or degree of electron beam pre-bunching and optimum parameters of wiggler tapering are found by the successive runs of the simulation code.

Földes and Pokol in their letter “Inertial fusion without compression does not work either with or without nanoplasmonics” criticized our works. Here, we refute their argumentation. Our proposed improvement is the combination of two basic research discoveries: (i) the possibility of detonations on space-time hypersurfaces with time-like normal (i.e., simultaneous detonation in a whole volume) and (ii) to increase the ignition volume to the whole target, by regulating the laser light absorption using nanoantennas. These principles can be realized in an in-line, one-dimensional configuration, in the simplest way with two opposing laser beams as in particle colliders.

The X-ray emissions in the interaction of 3–6 MeV Xe23+ ions into thick solid In target are measured. The projectile-to-target and target Lα/Lβ X-ray production intensity ratios are observed to strongly depend on the projectile energy. The dependence deviates from Coulomb ionization predictions, which implies the important roles of coupling between subshells and the activation of 4fσ rotational couplings for projectile energy larger than 5 MeV.