Thomson scattering measurement of electron density and temperature of a microwave plasma produced in a hydrogen gas at a moderate pressure

Laser Thomson scattering was applied successfully for the first time to a m icrowave discharge plasma suitable for deposition of diamond thin film. The plasma was produced in purl hydrogen gas, but the conditions were otherwis e identical to those used for diamond deposition. The local electron densit y and temperature at the plasma center were (3.0 +/- 0.2) x 10(17) m(-3) an d (1.7 +/- 0.2) eV. Although the degree of ionization of the plasma was ver y low (<10(-6)), Thomson scattering signals could be detected clearly by us ing a double-monochromator which has a stray light rejection of 10(-6) at t he differential wavelength of <Delta>lambda = 1 nm from the laser wavelengt h. Various checks were made to exclude the possibility of the probing laser from affecting the measured values, confirming the reliability of the meas urement.