arXiv subjects

Arvinder S. Sandhu

Publications and source records attributed to Arvinder S. Sandhu.

6 recordsLinked to original sources

arXiv2011

Real-time evolution of a laser-dressed Helium atom: Attosecond-resolved two-color photoionization study

Using extreme-ultraviolet attosecond-pulse-trains, we investigate the photoionization dynamics of a Helium atom in the presence of moderately-strong (~10^12 W/cm^2) femtosecond laser pulses. The electronic structure of a laser-dressed atom is traced in real-time through precision measurements of ion-yields and photo-electron angular distributions. Quantum interferences between photo-excitation paths are interpreted using the Floquet formalism. As the laser pulse intensity ramps on femtosecond timescales, we observe transitions between ionization channels mediated by different atomic resonances. The quantum phase of interfering paths is extracted for each channel and compared with simulations. Our results elucidate photoionization mechanisms in strong-fields and open the doors for photo-absorption/ionization control schemes.

physics.atom-ph↗

arXiv2011

Response of graphene to femtosecond high-intensity laser irradiation

We study the response of graphene to high-intensity 10^11-10^12 Wcm^-2, 50-femtosecond laser pulse excitation. We establish that graphene has a fairly high (~3\times10^12Wcm^-2) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation that leads to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of CVD graphene under femtosecond near-IR irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.

cond-mat.mtrl-sci↗

arXiv2003

Study of Coherent and Incoherent Plasma Emissions: Role of Plasma Wave Excitation and Breaking

Here we experimentally map the dynamics of electron plasma waves in laser solid interaction. We do time resolved measurements of second harmonic and hard X-ray generation from interaction of intense ($10^{16} W cm^{-2}$, 100 fs, 800nm) laser with a pre-plasma generated on a solid surface. The parameter space explored in this time resolved study includes variation of scale length, laser polarization and laser intensity in conjunction. These measurements done together brings novel features of strongly driven electron plasma wave behavior, which have not been explored experimentally so far. We model the results in terms of Resonance Absorption and Wave-Breaking mechanisms. The Harmonic and X-ray emission show contrasting behaviour, which indicates pitfalls in trying to increase harmonic efficiencies by brute force. However by simple adjustments, we observe that hard X-rays can be enhanced or controlled upto two orders of magnitude and second harmonic upto one order of magnitude under optimum conditions. These results should help us understand the governing mechanisms for short wavelength generation and fast particle generation to develop more efficient sources for application purposes.

physics.plasm-ph↗

arXiv2002

Evolution of Electrical Resistivity, Thermal Conductivity, and Temperature of a solid under the action of Intense Ultrashort Laser pulse

The dynamical properties of Cu in a regime relevant to femtosecond micro machining are obtained on picosecond time scales using pump-probe reflectivity study for 100fs, 1015 W cm-2 laser pulses. The electrical resistivity is obtained by solving Helmoltz equations. The dissipation mechanisms and scaling laws are obtained in high and low temperature limits. The 'resistivity saturation' effect in an unexplored regime intermediate to hot plasma and cold solid is studied in detail. The temperature evolution and thermal conductivity is obtained in the temporal range 0 to 30ps after the interaction of laser pulse with solid Cu.

physics.plasm-ph↗

arXiv2001

Roughness enhanced K x-ray emission from femtosecond laser produced copper plasmas

K x-ray emission from copper plasmas produced by 100 fs, 806 nm laser pulses at intensities in the range of 10^15-10^16 W cm^-2 is studied with respect to input laser polarization and target surface conditions. We demonstrate that even moderate surface roughness enhances the characteristic x-ray yield by as much as 70 %. We further show that surface roughness of the targets overrides the effect of polarization state in light coupling to the plasma.

physics.plasm-ph↗

arXiv2000

Suppression of Supercontinuum Generation with Circularly Polarized Light

Controlling a nonlinear process like supercontinuum generation (SG) with the polarization-state of laser is an important demonstration of laser selectivity. We show that the threshold for SG and the total amount of supercontinuum generated depends on incident laser polarization for isotropic samples. Irrespective of the nature of the samples chosen, SG efficiency decreases as the incident laser polarization changes from linear to circular and thus, provides the first experimental demonstration of the suppression of SG with circularly polarized light. The ratio of the overall SG between the linear and circular polarization (i.e., measure of suppression) undergoes an intensity dependent decrease from large initial values to asymptotic limits, irrespective of samples.

physics.optics↗