Laser Thomson scattering studies of glow discharge plasmas

Abstract

This paper describes the developments of laser Thomson scattering (LTS) for measuring electron density and temperature, or more generally electron energy distribution function (eedf) in glow discharge plasmas with electron densities below 10 18 m −3 . A brief description of the method for overcoming the sparcity of scattered photons by data accumulation techniques is followed by examples of applications, conducted at the authors' laboratory, to the measurement of the shape of the eedf and temperature anisotropy in various discharges including reactive plasmas, and some as close as 100 µm from a material surface. Measurements of the latter sort should permit the elucidation of micro-discharges and electrode effects such as cathode fall phenomena in particular.

An Investigation of the Plasma Composition in Plasma-enhanced Hot Filament Catalytic Chemical Vapor Deposition of Carbon Nanotubes

“…For the electron density n e-, the values calculated are 1.8 9 10 11 and 5.6 9 10 11 cm -3 without and with filaments, respectively. These values correspond to a mole fraction of 3.3 9 10 -6 and 1.05 9 10 -5 , respectively, in good agreement with a theoretical estimation [30] and simulations performed in similar processes like microwave discharges [14,48,49] and DC discharges [50,51]. Even if it must be recalled that such comparisons may be handled with care because of different experimental conditions (gas, pressure, plasma power, experimental set up, ...), nevertheless the same order of magnitude is found.…”

Applicabilities of Laser Thomson Scattering to Various Kinds of Discharge Plasmas.

“…2, a useful means of checking the laser perturbation of plasmas was described so as to determine whether electron properties be changed by the change in laser photon energies, or by the change in laser pulse energies. For the former tests, we developed an infrared LTS system [7], in which LTS signals from the fundamental wavelength of the YAG laser (1,064 nm) are detected using a sensitive infrared photomultiplier, in addition to using the second harmonic generation (SHG) of a YAG laser, which operates at 532 nm [1][2][3][4].…”

“…After a decade of systematic development work, incoherent laser Thomson scattering (LTS) has become an established and indispensable method for studying electron properties [electron density and electron temperature, or, more generally, electron energy distribution function (eedf)] in glow discharge plasmas in inert gases having an electron density in the range of 10 15 -10 20 m -3 [1][2][3][4]. The key technique of this LTS is data accumulation over many laser shots, usually more than a few thousand shots, by using high repetition lasers such as a YAG laser and/or its second harmonic, to obtain good S/N ratios.…”

Impedance property of lightning impulse discharge in short composite gap consisting of air and water

“…Existing methods for determining plasma resistance include the triple probe (TP) method [1,2] and laser Thomson scattering (LTS) [3,4]. These methods usually require knowledge of the plasma electron temperature (T e ) and electron density (n e ) so that Spitzer's expression can be used for the resistivity [5].…”