A new method of electron density measurement applied to a cw 337 μm HCN gas laser

This paper 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. The foregoing condition, which is sufficient to ensure laser action in a single mode only, is satisfied by most submillimetre lasers. 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 use of a relatively narrow resonator beam reduces this double average to the longitudinal average of the central electron density to a good approximation. The method is applied to two 337 μm HCN laser gas discharges in 5 cm and 10 cm diameter tubes, for conditions corresponding to maximum power output. The variation of electron density with gas pressure and discharge current is measured for both lasers. (author)