Abstract
Describes a method of electron density measurement which may be applied to those continuous submillimetre wave lasers for which the lasing-mode spacing is larger than the laser emission linewidth. This condition ensures laser action in a single mode only. The experimental principle is the measurement of the electronic contribution to the resonant length for a fundamental mode of the laser resonator. The result is a double average of the laser discharge electron density across the diameter of the laser resonator beam and along the length of the gas discharge. The method is applied to two 337 mu m HCN laser gas discharges under conditions corresponding to maximum power output.