Optically thin plasma

Here the emissivity term j o = luxic o) corresponds to the spontaneous emission. Radiation of the optically thin plasma is a result of the summation of independent emission from different intervals dx along the ray. Radiation generated within the plasma volume is able in this case to escape it. Assuming uniformity of the plasma parameters, the radiation intensity on the plasma surface can be expressed as... 

Thus, the radiation intensity of the optically thin plasma is much less (r, <[Pg.114]

In a flame, as the concentration of atoms increases, the possibility increases that photons emitted by excited atoms in the hot region in the centre will collide with atoms in the cooler outer region of the flame, and thus be absorbed. This self-absorption effect contributes to the characteristic curvature of atomic emission calibration curves towards the concentration axis, as illustrated in Fig. 4.4. The inductively coupled plasma (ICP) tends to be hotter in the outer regions compared with the centre—a property known as optical thinness—so very little self-absorption occurs, even at high atom concentrations. For this reason, curvature of the calibration curve does not occur until very high atom concentrations are reached, which results in a much greater linear dynamic range. 

Martin, P.J., Bendavid, A., Netterfield, R.P., Kinder, T.J., Jahan, F. and Smith, G. (1999), Plasma deposition of tribological and optical thin film materials with a filtered cathodic arc source , Surface and Coatings Technology, 112, 257-260. 

Because of the low spectral background intensities the limits of detection from the side of the source will be low and for metals will be down to the pg/g range in a classical Grimm lamp [479]. Also elements such as B, P, S, C, As,... can be determined. The plasma is optically thin, but for resonance lines of the matrix elements,... 

As viewed from the top, the plasma has a circular, doughnut shape. The sample is injected as an aerosol through the centre of the doughnut. This characteristic of the source confines the sample to a narrow region and provides an optically thin emission source and a chemically inert atmosphere. Normally, samples are introduced as a solution into the plasma and argon is used as a carrier gas for the sample introduction. The much higher temperatures of the plasma compared to flame make ICP-AES more effective in detecting lower concentrations of refractory elements such as Ta, W and Zr, and rare earth elements. 

Radiation Transfer in Plasma Optically Thin and Optically Thick Plasmas... 

CTE is not realized in laboratory plasmas wich are optically thin (Planck s law is not valid). But the mass action law, the Boltzmann distribution and Maxwell distribution may be obeyed by a unique local temperature such that T, = T e = T = T, then one introduces the (complete) local thermodynamic equilibrium (LTE). Boltzmann and Saha s law are often obeyed only for highly excited levels, the plasma is then said to be in Local Partial Thermodynamic Equilibrium (LPTE). 

Basically, the nitrogen plasmas in our low-pressure ( 1 Torr) steady-state discharge can be considered to be optically thin, at least for the 2PS band. This is because the order of electron density is IQis cm-3 at most, and the number density of the lower level is considered to be low enough for us to neglect reabsorption.i Under the optically thin condition, the intensity of the spectrum is proportional to the population density of the upper level Nc(p, / ) and the transition probability -... 

Popov, C., Zambov, L. M., Plass, M. R, and Kulisch, W., Optical, Electrical and Mechanical Properties of Nitrogen-rich Carbon Nitride Films Deposited by Inductively Coupled Plasma Chemical Vapor Deposition," Thin Solid Films, Vol. 377-378,2000, pp. 156-162. 

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