Abstract: Relativistic oscillations are realized in Laboratory using intense ultrashort laser interacting with solid and nanostructure targets. Their study reveals various interesting aspects of laser plasma coupling at extremely high intensities. Conventional understanding shows that light goes beyond the critical density (nc) due to relativistic mass effect the plasma transparency is enhanced and light goes up to γ(t)nc. We find the transparency may be quite different and light may go up to γ3(t)nc due to nonlinear resonance. It is further shown that non linear resonance in intense laser cluster and nanoparticle interaction is dynamically met due to time varying mass. This results in anomalous resonance densities which is different than the conventional value of resonance density of 3 nc and 2nc of spherical and cylindrical nanoparticles. Resonance are related to the time dependent Lorentz factor γ(t) which must be evaluated numerically in realistic situations. However we obtain its approximate variation in different ways to see its effect in modifying the resonance density. For this the analogy of variable mass oscillators is borrowed which are not just for pedagogical interest but their study is relevant to understanding the complex phenomenon of relativistic oscillations. Based on the understanding of variable mass oscillators it is noted that time varying mass acts as an effective damping which increases the resonance density. This analytical study will give meaningful insight to help in choosing the nanostructure oscillators /targets and intense laser parameters to achieve resonance at high density and consequently efficient hot electron, ion and x-ray generation.
Keywords: Ultrashort Lasers, Laser Plasma Interaction, Relativistic Oscillator, Driven Oscillators, Nanostructures, Gas Clusters, Non linear interaction, Damping in light matter interaction, Linear and non linear resonance.
Title: Anomalous Resonances and Relativistic Transparency for Ultra-high Intensity Laser Plasmas
Author: Uday Chakravarty
International Journal of Interdisciplinary Research and Innovations
ISSN 2348-1218 (print), ISSN 2348-1226 (online)
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