Optical characterisation of a low temperature plasma jet

They therefore have the potential to be used for various applications, in plasma medicine and surface modification in particular. The characterisation of these plasma jets is important in order to be able to control them for the desired application.<br><br>Various optical diagnostics have been implemented to establish the formation and propagation of the plasma, as well as to estimate the important parameters such as electron density, <i>n_e</i> , and electron temperature, <i>T_e</i>.

Initially imaging on nanosecond timescale established that the plasma, although continuous to the naked eye, consisted of plasma bullets travelling at velocities of up to 10⁵ m s⁻¹. 2D quasi monchromatic images of the plasma, obtained by isolating the light produced by individual spectral transitions, allowed an estimation of the density of excited helium states within the plasma, in the region of 1 × 10⁹ − 2 × 10¹⁰ cm⁻³.<br><br>Optical emission spectroscopy was used to identify the species present, to estimate the electron temperature of the plasma using helium line ratios, and to estimate the gas temperature using nitrogen emission.