ELECTRON-DENSITY MEASUREMENT IN A RF HELIUM PLASMA BY LASER-COLLISIONINDUCED FLUORESCENCE METHOD

Laser-collision induced fluorescence (LCIF) is the emission of light f rom states that have been populated by laser excitation and a subseque nt collision. By simultaneously measuring the LCIF from two different states, it is possible to determine both the electron density and temp erature of the low energy bulk electrons within a plasma. This method is described in detail and has been applied in the determination of th e total, temporally averaged, and spatially resolved electron density in a rf (13.56 MHz) helium discharge in the Gaseous Electronics Confer ence reference cell. The rf discharge was operated at pressures P=33.3 -133.3 Pa (0.25-1.0 Torr) and peak-to-peak voltages of V-pp=75-300 V w ere applied. We found the total electron density varied from 1.8X10(8) cm(-3) at P=33.3 Pa and V-pp=75 V to 4.0x10(10) cm(-3) at P=133.3 Pa and V-pp=300 V. A comparison of results from different experiments has been made. (C) 1996 American Institute of Physics.