Mapping neutral, ion, and electron number densities within laser-ablated plasma plumes

I. Weaver; Liam A. Doyle; G. W. Martin; Dave Riley; M. J. Lamb; William G. Graham; Tom Morrow; Ciaran L. S. Lewis

doi:10.1117/12.308637

26 May 1998 Mapping neutral, ion, and electron number densities within laser-ablated plasma plumes

I. Weaver, Liam A. Doyle, G. W. Martin, Dave Riley, M. J. Lamb, William G. Graham, Tom Morrow, Ciaran L. S. Lewis

Author Affiliations +

Proceedings Volume 3404, ALT'97 International Conference on Laser Surface Processing; (1998) https://doi.org/10.1117/12.308637
Event: ALT '97 International Conference on Laser Surface Processing, 1997, Limoges, France

Abstract

Spatially and temporally varying neutral, ion and electron number densities have been mapped out within laser ablated plasma plumes expanding into vacuum. Ablation of a magnesium target was performed using a KrF laser, 30 ns pulse duration and 248 nm wavelength. During the initial stage of plasma expansion (t <EQ 100 ns) interferometry has been used to obtain line averaged electron number densities, for laser power densities on target in the range 1.3 - 3.0 X 10⁸ W/cm². Later in the plasma expansion (t equals 1 microsecond(s) ) simultaneous absorption and laser induced fluorescence spectroscopy has been used to determine 3D neutral and ion number densities, for a power density equal to 6.7 X 10⁷ W/cm². Two distinct regions within the plume were identified. One is a fast component (approximately 10⁶ cm^-1) consisting of ions and neutrals with maximum number densities observed to be approximately 30 and 4 X 10¹² cm^-3 respectively, and the second consists of slow moving neutral material at a number density of up to 10¹⁵ cm^-3. Additionally a Langmuir probe has been used to obtain ion and electron number densities at very late times in the plasma expansion (1 microsecond(s) <EQ t <EQ 15 microsecond(s) ). A copper target was ablated using a Nd:YAG laser, 7.5 ns duration and 532 nm (2 (omega) ) wavelength, with a power density on target equal to 6 X 10⁸ W/cm². Two regions within the plume with different velocities were observed. Within a fast component (approximately 3 X 10⁶ cms^-1) electron and ion number densities of the order 5 X 10¹² cm^-3 were observed and within the second slower component (approximately 10⁶ cms^-1) electron and ion number densities of the order 1 - 2 X 10¹³ cm^-3 were determined.

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I. Weaver, Liam A. Doyle, G. W. Martin, Dave Riley, M. J. Lamb, William G. Graham, Tom Morrow, and Ciaran L. S. Lewis "Mapping neutral, ion, and electron number densities within laser-ablated plasma plumes", Proc. SPIE 3404, ALT'97 International Conference on Laser Surface Processing, (26 May 1998); https://doi.org/10.1117/12.308637

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