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Laser-plasma interaction

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Saved by Ayush Gupta
on July 29, 2008 at 10:43:10 am

Summary of Doctoral Research


Dissertation working title: "Interaction of Intense Short Laser Pulses with Gases of Atomic Clusters"

Advisor: Prof. Thomas M. Antonsen, Jr.


     Clusters are nanometer-sized solid density atomic aggregates bound by Van der Waals forces ranging in size from 10_u2 – 106 atoms. When a gas, under controlled temperature and pressure, is ejected into a vacuum chamber, it rapidly expands and cools down resulting in an aggregation of gas molecules in the form of clusters. When irradiated by an intense laser pulse (peak intensity ~1014-1017 W/cm2), clusters absorb laser energy very efficiently, expand and explode. The volume average density of clustered gases is low but the clusters themselves are at solid density. This enables strong interaction of individual clusters with an irradiating laser pulse while still allowing propagation of the pulse through the clustered gas. The efficient coupling of laser energy into clustered gases makes them a unique media for studying non-linear laser-matter interaction and leads to many exciting applications such as generation of x-rays for tomography/lithography, production of fusion neutrons for a potential table-top neutron source, generation of energetic particles for use in laser-based accelerators, and higher harmonics generation for non-linear optics applications.


     I have performed 2D electrostatic particle-in-cell (PIC) simulations of explosion dynamics of a laser-irradiated cluster. A key result of our study was that there is a well-defined intensity threshold above which energetic electrons are created by a non-linear resonant absorption process. We generalized the conditions for strong absorption to a range of system parameters such as the laser peak intensity and pulse width for Argon and Deuterium clusters. Subsequently, we used the PIC results to compute the fusion yield from exploding Deuterium clusters for a range of laser pulse intensities.


     For studying the optical properties of cluster ensembles, we coupled a fluid plasma model of clusters to a Gaussian description of laser pulse. The key feature of this model was the combination of experimental consistency with computational simplicity leading to the first simulations of laser pulse propagation through clustered gases. We have predicted parameter ranges for optimizing laser pulse guiding through clustered gases and explained observed phenomenon such as plasma wave guide formation, and spectral red shifts in the transmitted pulse. Self-guiding of laser pulses in a plasma channel is of particular consequence to laser-based acceleration.


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