Development of the third stage incoherent laser thomson scattering diagnostics of plasmas

We classify the incoherent laser Thomson scattering (LTS) diagnostics of plasmas for measurements of electron density ne and temperature Te (or more generally electron energy distribution functions; EEDFs) as having evolved from the first stage, in which a whole Thomson spectrum is obtained during a single laser pulse from plasmas having ne above 1018 m-3, through the second stage, in which data accumulation is prerequisite for ne below 1018 m-3, and to the third stage, in which measurements from a material surface as close as a few tens of μm is required. In this last case, a strong suppression of stray light in addition to the data accumulation is necessary, and this was first demonstrated for a PDP (plasma display panel)-like discharge in 2000. In order to further expand its applicable range, we have been pursuing a more systematic approach, taking into account factors such as laser propagation/profile control, further stray light suppression, and other aspects. In this review article, we describe these developments and discuss future plans. (author)