Sharif Digital Repository

Effect of thermal conduction on radiation from a single cavitating bubble has been studied in a hydrochemical framework including variation of heat conductivity of noble gases up to 2500 K. Results of numerical simulation show that thermal conductivity plays an important role in determining ultimate cavitation temperature. Higher thermal conductivity of lighter noble gases causes to more thermal dissipation during the bubble collapse, leading to a lower peak temperature. Moreover, at the same driving conditions, radius of light emitting region is greater for heavier noble bubbles. Therefore, sonoluminescence radiation is more intensive from heavier noble gases. Phase diagrams of... 

An effective semi-classical method is introduced for controlling the high-order harmonic generation process and extending the cutoff frequency. This method is capable of defining the proper specification of the driving laser for maximizing the cutoff frequency. This method is evaluated by examining the high harmonic spectrum from the hydrogen atom and the fluorine (F2) molecule irradiated by single-, two-, and three-color laser fields. This study is done using the time-dependent density functional theory in a three-dimensional space. The results show that the single-, two-, and three-color laser pulses tuned by proper specifications could extend the cutoff frequency by up to 85%, 176%, and... 

In this work, the optical properties of asymmetric nanoshells with different geometries are comprehensively investigated in the quasi-static regime by applying the dipolar model and effective medium theory. The plasmonic behaviors of these nanostructures are explained by the plasmon hybridization model. Asymmetric hybrid nanoshells, composed of off-center core or nanorod core surrounded by a spherical metallic shell layer possess highly geometrically tunable optical resonances in the near-infrared regime. The plasmon modes of this nanostructures arise from the hybridization of the cavity and solid plasmon modes at the inner and outer surfaces of the shell. The results reveal that the... 

A pair of copper vapor lasers in an oscillator-amplifier configuration were used to investigate the temperature dependence of the small-signal gain and saturation intensity and output power of the laser at the 510.6 and 578.2 nm transitions individually. An optimum working temperature of 1520°C was determined, and a maximum output power equivalent to 33 W/l was extracted  

The well-known Rayleigh-Plesset (RP) equation is the base of nearly all hydrodynamical descriptions of the sonoluminescence phenomenon. A major deficiency of this equation is that it accounts for viscosity of an incompressible liquid and compressibility, separately. By removing this approximation, we have modified the RP equation, considering effects of liquid second viscosity. This modification exhibits its importance at the end of an intense collapse, so that the new model predicts the appearance of a new picosecond bouncing during high-amplitude sonoluminescence radiation. This new bouncing produces very sharp (sub-picosecond) peaks on the top of the sonoluminescence pulse. These new... 

The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability  

The interaction of laser pulses of picosecond duration and terawatt to petawatt power accelerated for the very fast undistorted plasma blocks for deuterium DD or deuterium tritium fast ignition is investigated. Based on the direct and instant conversion of laser energy into mechanical motion by nonlinear (ponderomotive) forces, any thermal pressure generation is delayed by the collision process. Following the studying of the classical collision frequency, it is found that the quantum modified collision at higher energies results in a correction by about 15% reduction of the delay  

In this work, the optical responses of Fe3O4@Au and Fe3O4@Ag are comprehensively investigated using the discrete dipole approximation. It is found that the resonance wavelength and absorption efficiency strongly depend on the composition of the core and shell, geometry of the nanoparticles, core to particle volume ratio, core radius and shell thickness. The strongest impact is due to the shell material, the shape of the nanoparticles and their combination. When the composition of the shell is changed from gold to silver, instead of one fundamental resonance peak the absorption spectrum shows two, corresponding to the bonding plasmon mode at the nanoparticle-environment interface and...