Mohammad Hossein Mahdieh

Enhancing the conversion efficiency and maximum energy of laser-driven ion beams is a critical challenge for applications in hadron therapy and high-energy density physics. In this work, we present a comprehensive two-dimensional Particle-In-Cell (PIC) simulation study comparing Target Normal Sheath Acceleration (TNSA) from standard flat foils and novel annular sector (C-shaped) targets. Under identical ultra-intense laser irradiation (a0=10, tau=25 fs), the annular sector geometry demonstrates a substantial enhancement in acceleration performance driven by two synergistic mechanisms: electromagnetic cavity confinement and geometric plasma focusing. Our analysis reveals that the target void acts as an optical trap, sustaining oscillating electromagnetic fields for over 300fs via multiple internal reflections. This confinement results in a total laser energy absorption of 49% (compared to 16% for flat targets), which yields a peak electron temperature of 5.1 MeV more than double the 2.2MeV observed in flat targets. Furthermore, phase space diagnostics confirm that ion bunches accelerated from the converging cavity walls superimpose at the geometric center, creating a localized high-density focal spot. Consequently, the annular target increases the proton cut-off energy to 22MeV (vs. 12MeV for flat targets) and boosts Carbon ion energies beyond 60MeV. These findings establish that tailoring target curvature to exploit optical trapping and geometric focusing offers a robust pathway for developing compact, high-efficiency laser-ion sources.

In the present paper we have performed sets of experiments to study laser triggering high voltage switch. In this study, instead of electrical diagnostics, optical technique was utilized to characterize the discharge process. A Q-switched nanosecond Nd:YAG laser was used for triggering the switch. Dynamics of discharge, and the time delay of laser produced pre-plasma was monitored by fast photo diode signal which was connected to a fast oscilloscope. The spectrum of discharge emission was also recorded by photo spectrometer from which plasma parameters i.e. electron temperature, and density were estimated.

The nonlinear propagation of small amplitude dust acoustic solitary waves (DASWs) in a magnetized dusty plasma, containing Boltzmann distributed electrons of two distinct temperatures (low and high electron temperatures), negatively charged dust particles, and ions with two distinct temperatures (low and high ion temperatures) following Boltzmann distribution, is studied by deriving the Korteweg–de Vries (K–dV) equation. It is found that the characteristics of DASWs are significantly modified by two different temperature electrons (as well as ions), the external magnetic field, obliqueness of the system, and the number densities of two types of ions. It is shown that both compressive and rarefactive dust acoustic solitons occur in this case.

Nonplanar two-dimensional (2D) spherical dust acoustic solitary waves (DASWs) in unmagnetized, collisionless, Boltzmann distributed electrons, negatively c

Herein, Ag nanoparticle (NP) films are fabricated by pulsed laser deposition technique in the flowless atmospheric air. A Q‐switched Nd:YAG pulsed laser beam is used for the ablation process. The fabricated NP films are postirradiated by the pulsed laser beam. In addition, as‐deposited NP films are annealed in argon gas flow ambient for 45 min at different temperatures (250, 350, and 450 °C), and also annealed at 450 °C for 15, 30, and 45 min. The characteristics of fabricated NP films are investigated after postirradiating by pulsed laser beam, and thermal annealing in Ar gas flow. UV–vis absorption spectroscopy is utilized to provide surface plasmon resonance (SPR) characteristics of films. The results show that thermal annealing can lead to strong enhancement, and also narrowing of the SPR spectrum. The results of field emission scanning electron microscopy and atomic force microscopy show that the annealing and postirradiation processes can influence the NPs size and film structure. As an application, the fabricated film is utilized for surface‐enhanced Raman spectroscopy (SERS) using a 10⁻⁶ molar aqueous solution of Rhodamine 6G. The SERS results indicate that the annealed NP films become more sensitive than the as‐deposited films.

The dispersion relation and instability of dust acoustic waves (DAWs) in an unmagnetized dusty plasma with two different temperatures for ions, two different temperatures for electrons, and dust charge fluctuations are investigated. Ions and electrons are assumed to be Maxwellian distributed. The orbital limited motion theory (OLM) is used to derive dust charge fluctuations. The conditions for the instability are found to be significantly modified by the effects of two different temperatures of ions (electrons), dust charge fluctuations, density ratio of ions and density ratio of electrons. Furthermore, it is observed that there is only damping rate in such dusty plasma.

The propagation of dust acoustic solitary waves (DASWs) has been investigated in a magnetized dusty plasma consisting of negatively charged dust particles, nonthermal ions and nonthermal electrons. Using reductive perturbation method, the Korteweg-de-Vries (K-dV) equation is derived. It is found that the basic structures (such as polarity, amplitude, width) of DASWs are influenced by nonthermal ions and nonthermal electrons. The results show that both compressive and rarefactive DASWs exist in such dusty plasma. It is observed that by increasing the nonthermality parameter of ions and electrons, the nonlinear wave phase velocity increases. Furthermore, nonthermal distributed ions have more effect on the nonlinear wave phase velocity of the DASWs than nonthermal distributed electrons. The dependence of the angle that the external magnetic field makes with the propagation direction of wave on the amplitude and width of DASWs has been also investigated. It was concluded that this angle strongly affects the DASWs. Finally, the effect of the magnetic field appears only in the width and not in the amplitude of the DASWs. The findings of this study can be helpful in understanding the structures of DASWs in the dusty plasma in which both nonthermal ions and nonthermal electrons exist. Such structures can be found in different regions of space and astrophysics mediums such as the upper ionosphere and Saturn’s E-ring.

Nonlinear dust acoustic solitary waves (DASWs) in an unmagnetized dusty plasma with a negatively charged dust fluid are studied in bounded two-dimensional (2D) cylindrical geometry. The dusty plasma was assumed to have electrons with Boltzmann distribution and ions with vortex-like distribution. Transverse perturbation was observed in such dusty plasma. By using the reductive perturbation method along with new space-time stretched coordinates, modified Korteweg–de Vries (K–dV) equation was derived for cylindrical geometry. Particularly, exact solution for the modified K–dV equation in 2D cylindrical geometry was obtained. The solution was investigated for different physical parameters of the plasma. It has been found that the trapped ions have significant effect on the properties of nonlinear waves (small but finite amplitude and width) in cylindrical geometry. The results also show that only compressive solitary waves can be formed in this system. According to the results, the properties of the DASWs in 2D cylindrical geometry differ from 1D cylindrical geometry. Furthermore, unlike the planar modified K–dV equation, in cylindrical modified K–dV equation, solitary structures are slightly deformed in time. The results of present investigation may help to understand the nature of DA solitary structures where dust along with non-Maxwellian ions exists. Such structures can be found in different regions of space and astrophysics mediums.