The electron drift velocity, the longitudinal diffusion coefficient, the effective ionization coefficient and the limiting field strength for mixtures of SF 6 with CHF 3 and CF 4 have been measured with a pulsed Townsend technique. The overall density-reduced electric field strength, E/N, could be varied between 60 and 520 Td (1 Td = 10 −17 V cm 2 ), while the SF 6 content in the gas mixtures was varied over the range 1-50%. We have found that the electron drift velocity and the density-normalized longitudinal diffusion coefficient vary weakly with the amount of SF 6 in the mixture. In contrast, the effective ionization coefficient shows a strong dependence with the SF 6 content, becoming more electronegative as the amount of SF 6 is increased. The measured limiting field strength for these two mixtures is lower than those for SF 6 -N 2 . To our knowledge, no previous ionization or electron transport data for these mixtures have been published.

It is found that a long conventional c\v CO1 laser cannot be tuned selectively because of the multidirectional modes formed through reflections at grazing angles from the inner walls of the discharge tubes. This problem has been overcome by inserting a number of properly designed mode-selecting apertures right into the discharge tubes and selective tuning over more than l50 rotational lines in both P and R branches of three vlbrational bands (9.6.10.6 and 11.2 pm) has been achieved. The rotational lines of higher/-values that have a low gain tend to lase in the TE\l,o mode. In the R branch two consecutive lines are observed to lase simultaneously when the angular width of the active medium subtended at the grating allow the existence of two physically tilted beams of different wavelengths dispersed by the grating used. The output poser distribution over various lines almost follows that of the gain. The optimum design parameters of a long c\v CO, laser for tuning are obtained.

No abstract