A Thomson scattering diagnostic, using an intensified gated charged coupled device detector and a high-repetition rate yttrium aluminum garnet laser, was utilized to measure electron parameters in a radio-frequency discharge. Both inductively and capacitively coupled plasmas in argon and argon–oxygen mixtures were studied, with electron densities as low as ∼5×109 cm−3. Different modes of detection (direct accumulation and photon counting) have been compared. The photon counting technique has been used to provide better accuracy at low light level (i.e., low electron densities). The results are compared with Langmuir probe measurements performed under the same plasma conditions, and good agreement is found between the two diagnostics.

A crystalline hydrogenated carbon film obtained by plasma enhanced chemical vapor deposition

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Incoherent Thomson scattering (ITS) provides a nonintrusive diagnostic for the determination of one-dimensional (1D) electron velocity distribution in plasmas. When the ITS spectrum is Gaussian its interpretation as a three-dimensional (3D) Maxwellian velocity distribution is straightforward. For more complex ITS line shapes derivation of the corresponding 3D velocity distribution and electron energy probability distribution function is more difficult. This article reviews current techniques and proposes an approach to making the transformation between a 1D velocity distribution and the corresponding 3D energy distribution. Previous approaches have either transformed the ITS spectra directly from a 1D distribution to a 3D or fitted two Gaussians assuming a Maxwellian or bi-Maxwellian distribution. Here, the measured ITS spectrum transformed into a 1D velocity distribution and the probability of finding a particle with speed within 0 and given value v is calculated. The differentiation of this probability function is shown to be the normalized electron velocity distribution function.