Revision of the criterion to avoid electron heating during laser aided plasma diagnostics (LAPD)

A criterion is given for the laser fluency (in J/m super(2)) such that, when satisfied, disturbance of the plasma by the laser is avoided. This criterion accounts for laser heating of the electron gas intermediated by electron-ion (ei) and electron-atom (ea) interactions. The first heating mechanism is well known and was extensively dealt with in the past. The second is often overlooked but of importance for plasmas of low degree of ionization. It is especially important for cold atmospheric plasmas, plasmas that nowadays stand in the focus of attention. The new criterion, based on the concerted action of both ei and ea interactions is validated by Thomson scattering experiments performed on four different plasmas.