Electron collection radius of an electrostatic probe immersed in a low-pressure plasma

A technique is described for determining the electron collection distance by an electrostatic probe. A pulsed laser beam coaxial with the probe creates, by the photodetachment of plasma negative ions, a burst of electrons. The measurement of the amplitude of the probe electron current pulse as a function of the laser beam diameter indicates that the electron collection distance by the probe is twice the sheath thickness given by Kiel.