Laser excitation in silicon from femto- to pico-second time scales is studied. We assume the Three-Temperature Model (3TM) which describes the dynamics of the distinct quasi-temperatures for electrons, holes, and lattice. Numerical results for damage threshold reproduce the experimental results not only quantitatively, but qualitatively as well, showing dependence on laser pulse duration. Comparison with experimental data suggests that electron emission and thermal melting are both responsible for damage in silicon. We found that electron-phonon relaxation time has a significant effect on pulse duration dependence of electron emission.

In this work, we have studied the interaction dynamics of the intense sub-cycle laser with the Xe2600 (Xenon) cluster by using a molecular dynamic code. The code is benchmarked against a couple of experimental works on Xe clusters. In the sub-cycle regime, the plane wave prescription of the laser pulse is not adequate, giving unrealistic field profiles, and hence in this study, we have relied on complex-source based sub-cycle pulsed beam model, which is an exact solution of Maxwell's equations. In order to see the effect of the sub-cycle pulses, the laser pulse duration is varied from 0.2 to 1 laser cycle while keeping the pulse energy conserved (by varying the peak amplitude with pulse duration). It has been observed that for the same laser energy the more energetic ions are obtained for sub-cycle pulses. Although the cluster explosion is symmetric, higher charge states are observed along the direction of laser polarization. The conversion efficiency of the energy absorbed per atom to average kinetic energy is found to be maximum for the shortest pulse duration of 0.2 laser cycle. The scaling law for maximum ion energy, total energy absorbed, and average kinetic energy of the ions with laser pulse duration is also deduced.

The generation of higher harmonics of intense lasers and associated attosecond pulses is a field of contemporary interest which promises a variety of applications ranging from the fundamental to applied sciences. In this work, we have probed the interaction of the intense (≳10 19 W=cm 2 ) 248 nm laser with Deuterium clusters using classical molecular dynamics simulation. The Thomson scattered radiation emitted by the electrons is considered by using standard Liénard-Wiechert potentials. We have studied the angular distribution of the radiation emitted by electrons and observed that the ponderomotive force exerted by these highly intense laser pulses leaves a very distinct signature of the radiated energy along a particular direction, which in principle has its own diagnostic potential to directly measure the intensities of incident laser pulses. Furthermore, the interaction of lasers with intensities ∼10 19 -10 21 W=cm 2 with atomic clusters results in the attosecond burst of energy in form of electromagnetic radiations, which fall under the XUV to soft x-rays regime of electromagnetic spectrum. The parameters of the atomic clusters, e.g., size (number of atoms), atomic species, etc. can be easily controlled experimentally and these in turn, change the number of electrons participating in the interaction process and hence, the properties of Thomson scattered radiation can be tuned accordingly.

We study the interaction of intense, sub-cycle, and few-cycle laser pulses with xenon clusters for the generation of mono-energetic electron bunches. For this purpose, we used three dimensional, relativistic, molecular dynamics simulations. In this work, we used two mutually perpendicularly polarized (MPP) pulses separated by a finite temporal phase delay. The first pulse is responsible for the generation of electrons by field ionization of atomic clusters. However, the second pulse tends to accelerate the electrons (created by the first pulse) as a bunch. The effect of phase delay, pulse duration, and peak laser intensity on the generation of energetic electron bunches is studied. Under optimum conditions, the electrons are found to be accelerated to energies as high as 2.5 MeV. The feasibility of further acceleration of these electron bunches utilizing laser wakefield acceleration is also explored in this work by treating the accelerated electron bunch by MPP pulses as an initial condition to the nonlinear one-dimensional laser wakefield equations. The rough estimate of the final accelerated electron energies after laser wakefield acceleration has also been made.

Effect of laser wavelength on the carrier-phonon dynamics and damage threshold of silicon is studied numerically. Laser excitation dynamics in silicon is studied using Three-Temperature Model (3TM). We consider the evolution of electron, hole, and lattice temperatures separately and including band-gap re-normalization effect on optical properties of silicon. Finite Difference Time Domain method is used to model the laser field. Damage threshold calculated using the 3TM is in reasonable agreement with the experiments. Our results indicate that the competition of inter-band excitation, plasma heating, and electron–phonon relaxation process defines the damage threshold for various wavelengths and pulse durations.