Optimization of the geometrical dimensions of the cold cathode of a helium–neon laser

An investigation was made of the depth of penetration of a gas discharge into the cavity of a cylindrical cold cathode. This depth was determined as a function of the discharge current (from 5 to 100 mA), the pressure (from 0.62 to 5 mm Hg), and the ratio of the partial pressures of helium and neon (4:1, 6:1, 8:1, 10:1, 12:1). A mixture with the 6:1 ratio was used as an example to demonstrate the method for deriving the empirical dependence of the depth of penetration of the discharge on the factors listed above. The results of life tests indicated that a correct selection of the cathode geometry increased considerably the service life.