arXiv subjects

A. S. Sandhu

Publications and source records attributed to A. S. Sandhu.

5 recordsLinked to original sources

arXiv2005

Enhanced hard X-ray emission from femtosecond laser irradiated microdroplets

We make a comparative study of hard x-ray emission from 15 $μ$m methanol microdroplets and a plain slab target of similar atomic composition at similar laser intensities. The hard X-ray yield from droplet plasmas is $\simeq$ 35 times more than that obtained from solid plasmas. A prepulse that is about 10ns and about 5% of the main pulse is essential for hard x-ray generation from the droplets. A hot electron temperature of 36 keV is measured from the droplets at 8$\times10^{14}$ W cm$^{-2}$; three times higher intensity is needed to obtain similar hot electron temperature from solid plasmas with similar composition. We use 1D PIC simulation to obtain qualitative correlation to the experimental observations.

physics.plasm-ph↗

arXiv2004

Laser Generated Magnetic Pulses: Hot Electron Propagation in Conducting and Dielectric Material

We report experimental evidence of electrostatic inhibition of fast electrons, generated in a highly resistive material upon irradiation with an intense ultra-short ($10^{16} W/cm^{2}$, $100 fmsec$) laser pulse. The experiment involves measurement of temporal evolution of self-generated magnetic pulses using pump-probe polarimetry. A comparison is made between the temporal behaviour of magnetic pulses generated with Aluminum and Glass targets. It is found that in contrast to Aluminium, self-generated magnetic pulse decays much faster in glass. This is attributed to the absence of return shielding currents in glass, which results in build up of electrostatic field, which in turn inhibits the movement of fast electrons. Fitting of experimental measurements using a one dimensional model, yields estimate of conductivity of Aluminium and glass, and penetration depth of hot electrons in these materials.

physics.plasm-ph↗

arXiv2002

Metal nanoplasmas as bright sources of hard x-ray pulses

We demonstrate a 13-fold increase in hard x-ray bremsstrahlung (10 - 200 keV) emitted by a copper plasma created by 100 fs, 806 nm pulses at $10^{14}-10^{15}$ Wcm$^{-2}$. This enhancement is achieved by roughening the target surface with copper nanoparticles of ~15 nm size. A simple model that invokes local field modifications by surface plasmon excitation and `lightning rod' effects explains the observed enhancement quantitatively and provides pointers to the design of structured surfaces for maximizing the emission.

physics.plasm-ph↗

arXiv2002

Laser-Generated Ultrashort Multi-Megagauss Magnetic Pulses in Plasmas

We demonstrate ultrashort (6 ps), multi-Megagauss (27 MG) magnetic pulses generated upon interaction of an intense laser pulse (10^{16} Wcm^-2, 100 fs) with a solid target. The temporal evolution of these giant fields generated near the high density critical layer is obtained with the highest resolution reported so far. Particle-in-cell simulations and phenomenological modeling is used to explain the results. The first direct observations of anomalously rapid damping of plasma shielding currents produced in response to the hot electron currents penetrating the bulk plasma are presented.

physics.plasm-ph↗

arXiv2002

Role of surface roughness in hard x-ray emission from femtosecond laser produced copper plasmas

The hard x-ray emission in the energy range of 30-300 keV 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 investigated. We demonstrate that surface roughness of the targets overrides the role of polarization state in the coupling of light to the plasma. We further show that surface roughness has a significant role in enhancing the x-ray emission in the above mentioned energy range.

physics.plasm-ph↗