Particle modeling of microplasma generated by resonance enhanced multiphoton ionization

Siva Sashank Tholeti, Purdue University

Abstract

Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms. The REMPI technique typically involves a resonant single or multiple photon absorption to an electronically excited intermediate state followed by another photon which ionizes the atom. Rayleigh scattering of REMPI plasma has given rise to a non-intrusive, time accurate measurement of electron formation and loss, which lead to many applications viz. trace species detection and micro-plasma diagnostics. It is very important to quantify the expansion process and the evolution of energy of electrons and ions. The operation scale of this process is in microns and non continuum nature of the process lead to the use of PIC/MCC scheme to compu- tationally model REMPI technique. This work attempts to understand and analyze the processes taking place during the expansion of REMPI plasma computationally using the PIC/MCC scheme. One dimensional and two dimensional approximations are considered to analyze the REMPI plasma expansion in Argon gas generated by a laser with a focal shape of a prolate ellipsoid. The expansion of the plasma is found to be very sensitive to the initial velocity distribution of the electrons. REMPI plasma expansion is shown to be ambipolar in nature, with the radial expansion more predominant than axial expansion, hence requiring the 2D model. Electron energy distribution functions(EEDFs) are found at various radial locations along with the corresponding mean energies. The deviation of the EEDFs from that of equilibrium Maxwell-Boltzmann energy distribution is presented both qualitatively and quanti- tatively, indicating the predominant processes at various instances in time.

Degree

M.S.E.

Advisors

Alexeenko, Purdue University.

Subject Area

Aerospace engineering|Physics

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