Sharif Digital Repository

Propagation of a Gaussian x-ray laser beam has been analyzed in collisionless thermal quantum plasma with considering a ramped density profile. In this density profile due to the increase in the plasma density, an earlier and stronger self-focusing effect is noticed where the beam width oscillates with higher frequency and less amplitude. Moreover, the effect of the density profile slope and the initial plasma density on the laser propagation has been studied. It is found that, by increasing the initial density and the ramp slope, the laser beam focuses faster with less oscillation amplitude, smaller laser spot size and more oscillations. Furthermore, a comparison is made among the laser... 

The interaction of the sub-picosecond UV laser in sub-relativistic intensities with deuterium is investigated. At high plasma temperatures, based on the quantum correction in the collision frequency, the electron heating and the ion block generation in plasma are studied. It is found that due to the quantum correction, the electron heating increases considerably and the electron temperature uniformly reaches up to the maximum value of 4.91-×-107-K. Considering the quantum correction, the electron temperature at the laser initial coupling stage is improved more than 66.55% of the amount achieved in the classical model. As a consequence, by the modified collision frequency, the ion block is... 

Propagation of Gaussian X-ray laser beam is presented in collisional quantum plasma and the beam width oscillation is studied along the propagation direction. It is noticed that due to energy absorption in collisional plasma, the laser energy drops to an amount less than the critical value of the self-focusing effect and consequently, the laser beam defocuses. It is found that the oscillation amplitude of the laser spot size enhances while passing through collisional plasma. For the greater values of collision frequency, the beam width oscillates with higher amplitude and defocuses in a shallower plasma depth. Also, it is realized that in a dense plasma environment, the laser self-focusing... 

Small high-quality Au/p-Si Schottky barrier diodes (SBDs) with extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from currentvoltage (IV) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By extrapolating the plots the built-in potential of the Au/p-Si contact was obtained as Vbi=0.5425 V and the barrier height value (ΦB(C-V)) was calculated to be ΦB(C-V)=0.7145 V for Au/p-Si for a typical 100 μm diode diameters. In the present work the... 

High order harmonic generation is investigated for N2 and CO molecules under ten-cycle sin-squared laser pulse at 800 nm wavelength and I = 2 × 1014 W cm−2 intensity. In order to study effects of the asymptotic behavior of the exchange-correlation (XC) potentials, the time-dependent Kohn-Sham equations are numerically solved in the non-linear non-perturbative regime with four different XC potentials. Time-dependent electron localization function is used to get imaging on the temporal dependence of the electron density. Time-profile analysis was also utilized for studying long and short electron trajectories. It is found that the ionization energy values both molecules calculated by using... 

In this study, a novel scheme for fiber optic strain sensor has been introduced. This scheme is indeed a Mach-Zehnder interferometer followed by a displacement sensor. The strain is applied to an optical fiber which is the main branch of the Mach-Zehnder interferometer and causes an alteration in the interferometer's output intensity. The output beam is then spread on a mirror located in front of the fiber head. The head of the fiber and the mirror form a displacement sensor configuration. The portion of the reflected beam, gathered by the fiber, is a function of the distance between the fiber head and the mirror. So, applying strain causes a new change in the gathered intensity due to the... 

The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution... 

The lasing mechanism and temporal output profile of distributed feedback dye lasers is investigated, using a model based on induced polarization in the dye solution, where a more accurate behavior of the laser output is predicted. It is found that the temporal output profile of the laser is mostly determined by the concentration of dye solution and the lifetime of the upper laser level of dye molecules. To a large extent, the results of this work agree with experimental studies, even at high-level pump intensities where the self Q-switched model fails to be applied. Especially, the experimentally observed irregular intensity profile of laser output is explained. It is also shown that, when... 

Three magneto-plasmonic nanohybrids were synthesized using Au- and Ag-coated Fe3O4 nanoparticles (NPs)-modified dual pH- and temperature-responsive triblock copolymer of poly (butyl methacrylate-co-acrylamide-co-methacrylic acid) to serve as drug carriers with potential of using in both photothermal and controlled/targeted chemotherapies. The internal superparamagnetic core gives the carriers targeted-delivery characteristics, and surface plasmon resonance–based noble metallic Au/Ag shells give them on-demand photothermal and photo-triggering release properties. To investigate the effect of coating method on the targeting property of synthesized carriers, Au NPs were attached to the magnetic... 

The influence of liquid bulk viscosity on the dynamics of a single cavitation bubble is numerically studied via Gilmore model with a new modified boundary condition at bubble interface. In order to more accurately describe the interior gas thermodynamics, a hydrochemical model is used. The numerical results for an argon bubble in water and aqueous H2SO4 show that including the liquid bulk viscosity slightly affects the bubble dynamics in collapse phase. This effect becomes significant only at high ultrasonic amplitudes and high viscosities. Moreover, the maximum pressure value inside the bubble is much more influenced than the maximum temperature. This finding lends support to results of... 

New dual light/temperature-responsive nanocarriers were synthesized using bimetallic plasmonic Au-Ag and Ag-Au nanoparticles (NPs) as cores of vehicles which subsequently functionalized with an upper critical solubility temperature–based poly acrylamide-co-acrylonitrile using reversible addition-fragmentation chain transfer for spatiotemporally controlled chemo-photothermal synergistic cancer therapy. The bimetallic cores were assigned to sense wavelengths close to the localized surface plasmon resonance of monometallic NP shell to produce heat which not only can increase the surrounding temperature over the upper critical solubility temperature of polymer to open its valves and promote drug... 

The temporal and spatial evolution of the two counter-propagating laser waves inside the active medium of a gain coupled distributed feedback dye laser is studied via a dynamic model. More specifically, the feedback mechanism, the temporal and spatial evolution of laser waves, the interaction between them, and the effect of pump pulse characteristics on the feedback strength are explained. It is shown that a pumping configuration with a spatial Gaussian pattern strongly decreases the laser pulse energy. This has never proposed or described by other models in the literature. For a narrow Gaussian pump pulse, the distributed feedback lasing on both sides of the active medium vanishes and... 

The main effects of liquid compressibility on the dynamics of single bubble sonoluminescence are investigated via three different radial dynamics models. In order to precise description of the interior gas thermodynamics, a hydrochemical model is used. In the case of an argon gas bubble in water, the results obtained with the Gilmore model and the Lezzi and Prosperetti model are compared with those resulting from the Keller and Miksis model. It is shown that the variation of liquid density at bubble surface in a very short time interval around the end of the bubble collapse, which has been incorporated into the first two models, strongly influences the bubble cavitation dynamics at higher... 

We present a method for high-order harmonics generation of N2 and CO molecules under two-color circularly polarized counter-rotating laser pulses at frequencies of and 2. Pulse envelope in this investigation is sin-squared and the intensity of each laser beam is with ten-optical cycle (o.c.). We show that an isolated pulse with a pulse duration shorter than 20 attosecond from the superposition of several harmonics can be generated. Both two-color linearly- and bicircularly-polarized laser pulses are considered. Our results have also been compared with the outcomes of the previous theoretical works as well as experiment observations. It is found that for CO molecule, the... 

Laser ablation of titanium target in distilled water for synthesis of colloidal nanoparticles is studied both experimentally and theoretically. The effects of laser parameters such as wavelength, pulse energy, fluence and shot numbers on the ablation rate and size properties of colloidal nanoparticles are investigated. The experimental approach addresses the interesting issue for finding the optimal main experimental parameters of laser ablation. The theoretical thermal model of nanosecond pulsed laser ablation is developed to visualize the evolution of temperature distributions and ablation depth. The simulation result of ablation depth has been compared with the experimental result... 

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a... 

Measurement of extremely new phenomena during the interaction of laser pulses with terawatt and higher power and picoseconds with plasmas arrived at drastically different anomalies in contrast to the usual observations if the laser pulses were very clean with a contrast ratio higher than 108. This was guaranteed by the suppression of prepulses during less than dozens of ps before the arrival of the main pulse resulting in the suppression of relativistic self-focusing. This anomaly was confirmed in many experimental details, and explained and numerically reproduced as a nonlinear force acceleration of skin layers generating quasi-neutral plasma blocks with ion current densities above 1011... 

Material characteristics and input-field specifics limit controllability of nonlinear electromagnetic-field interactions. As these nonlinear interactions could be exploited to create strongly localized bright and dark waves, such as nonlinear surface polaritons, ameliorating this limitation is important. We present our approach to amelioration, which is based on a surface-polaritonic waveguide reconfiguration that enables excitation, propagation and coherent control of coupled dark rogue waves having orthogonal polarizations. Our control mechanism is achieved by finely tuning laser-field intensities and their respective detuning at the interface between the atomic medium and the metamaterial... 

The effects of liquid density variation at the bubble surface on the dynamics of a single acoustic cavitation bubble are numerically studied. The Gilmore model together with a comprehensive hydrochemical model is used. The evaporation and condensation of water vapor are included in the hydrochemical model. The simulation results are compared to those resulting from the widely known Keller-Miksis model, which assumes a constant liquid density at the bubble surface. The numerical results for a single argon bubble in water reveal that the pressure and the temperature inside the bubble in collapse phase significantly increase, when the non-constant liquid density is used. These differences... 

In this work we evaluate the interaction of high intense laser beam with a steepened density profile. During laser interaction with underdense plasma by freely expanding plasma regime, modification of density profile is possible. In this paper we have investigated the ultra short laser pulse interaction with nonisothermal and collisionless plasma. We consider self-focusing as an effective nonlinear phenomenon that tends to increase when the laser power is more than critical rate. By leading the expanded plasma to a preferred location near to critical density, laser reflection is obtained, so the density profile will be locally steepened. The electromagnetic fields are evaluated in this new...