Abstract

By using an external cavity ring laser, the radial distribution of the Langmuir flow null shift in discharge tube capillaries has been investigated. The experimental results are not in agreement with the current picture which predicts that the gas flow is in one direction at the center of the capillary and in the other direction near the wall, with a well-known radial distribution of velocity. Now the measured Langmuir flow null shifts caused by gas flow effects are only in one direction with a new radial distribution of the gas flow velocity. We explain the experimental results by introducing a reasonable physical picture: because of electron–atom collisions in the glow discharge, the atoms at different states have different average velocities that cause Langmuir flow null shift effects quite different from the current picture.

© 1986 Optical Society of America