Bonn 2000 – scientific programme

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P: Plasmaphysik

P 21: Dichte Plasmen (Poster)

P 21.2: Poster

Thursday, April 6, 2000, 17:00–19:30, Aula

Investigation of plasma plumes produced by a ruby laser impinging on boron-nitride slabs — •T. M. Atwee, L. Aschke und H.-J. Kunze — Institut für Experimentalphysik V, Ruhr-Universität Bochum

Spectra emitted from plasmas produced when a pulsed ruby laser is focused on boron-nitride and boron targets in the wavelength region 30−220 Å are investigated. A pinhole camera is used to study the expansion of the plasma plumes. Only the radiation below about 80 nm is essentially transmitted and detected by a gated MCP. In all investigations the laser is focused to a spot of 0.5 mm in diameter, the fluence thus is 1.5 kJ/cm², the irradiance about 7.6 · 10¹⁰ W/cm². The pinhole images illustrate the gross structure of the plasma plumes when the laser beam impinges perpendicularly onto a new target surface or at an angle of incidence of 60^∘. We study the drastic changes of plasma expansion when the depth of the hole increases by firing the laser several times on the target position. Inspection of the hole in the target reveals the hole is in the direction of the laser beam. This explains that the new direction of the plasma plume since now a large fraction of the plasma originates inside the hole and is ejected along the hole axis. With increasing depth of the hole the observed plasma plume outside the hole becomes shorter for all angle of incidence and the intensity of emission decreases. The plasma electron temperature is investigated using the relative line intensity ratio for heliumlike boron lines and the behaviour of the temperature due to the change of the depth of the hole in the target is studied.