A Basic Complete Numerical Toolbox for Picosecond Ultrasonics

A complete numerical complete toolbox is proposed concerning the simulation of photo-induced propagative mechanical wave, and concerning the optical reflectometric measured response of the material, which is initially exposed to a first pump laser beam that photo-induces the acoustic wavefronts. The deformation field and its propagation into a bulk material are simulated. Based on this field expression, the complex transient reflectivity is given for a medium considered as homogeneous. The real part of this quantity permits afterwards to propose a numerical simulation of the transient reflectivity, which corresponds to the optical signal measured during experimental works. The frequency acoustic spectrum is simulated and successfully compared to the measured frequency spectrum. For the first time, numerical complete developments are explicitly proposed and fully-developed under the SciLab ® environment, related to the simulation of laser-induced picosecond acoustic wavefront photogenerated through an opto-acoustic transduction process (ultrasonics and pretersonics).

Frequency measurement using Rayleigh scattering from a BEC

We propose to use superradiant Rayleigh scattering from degenerate Bose gas to detect unknown frequencies coupled to the pump laser beam. Theoretically we show a measurement of the time evolution of population at the initial momentum state could determine the unknown frequency with respect to a known one at which the pump laser's frequency modulates. We show a range of frequencies from kHz to MHz could be determined with this method at the currently available state-of-the-art technology.

Two Temperature Model Numerical Simulation and Analysis of Thermal Transport Process in Copper Film

Thermal transport process in copper film was numerically simulated with Two-Temperature Model, in which finite difference method was used, and the result shown the temperature change process in electron-lattice system. Some parameters were changed to carry on further simulation. The affect of film thickness on the electronic relaxation time was analyzed. The affect of pump laser beam power on the electron temperature rise was discussed. The influence of electron-lattice coupling factor G on non-equilibrium thermal process was shown in simulations.

Cross Focusing of two Coaxial Gaussian Beams with Relativistic and Ponderomotive Nonlinearity

This paper presents the cross focusing of two high power lasers by taking off-axial contributions of the laser beams in a collisionless plasma. Due to relativistic and ponderomotive nonlinearities the two laser beams affect the dynamics of each other and cross focusing takes place. The expressions for the laser beam intensities by using the eikonal method are derived. The contributions of the r2 and r4 terms are incorporated. By expanding the eikonal and the other relevant quantities up to the fourth power of r, the solution of the pump laser beam is obtained within the extended paraxial ray approximation. Filamentary structures of the laser beams are observed due to the relativistic and the ponderomotive nonlinearity. The focusing of the laser beams is shown to become fast in the extended paraxial region. Using the laser beam and the plasma parameters, appropriate for beat wave processes, the filaments of the laser beams are studied and the relevance of these results to beat wave processes is pointed out.

Generation of plasma wave and third harmonic generation at ultra relativistic laser power

This paper investigates the generation of plasma wave and third harmonic generation in hot collision less plasma by a Gaussian ultra intense laser beam, when relativistic and ponderomotive nonlinearities are operative. First, we derive the dynamical equation for the pump laser beam when these two nonlinearities are operative. The solution of pump laser beam has been obtained within the paraxial ray approximation. Filamentary structures of the laser beam are observed. On account of V→ × B→ force, the generation of plasma wave at second harmonic frequency has been studied in these filamentary structures. Interaction of the plasma wave with the incident laser beam generates the third harmonic. For the typical laser plasma parameters: Nd: YAG laser beam (λ = 1064 nm), ro = 15 µm, laser power flux equals 6 × 1017 W/cm2, electron density equals no = 1.9 × 1019 per cm3, the third harmonic yield comes out to be equals to 2 × 10−6.