Characteristics of a Low-Voltage Helium–Neon Laser

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Abstract
Laser oscillations of wavelength 3.39 μ are reported for a low‐voltage discharge in He–Ne (7:1 pressure ratio). This discharge, characterized by high current (1–2 A), low voltage (24–30 V anode bias), and negative resistance, used a triode laser tube design with plane‐parallel electrodes, a heated oxide‐coated cathode, a plasma stabilizing grid, and a movable anode. Laser outputs for a pressure range of 2.5–4.0 Torr, grid‐anode separations of 4.0–0.8 mm, and a cathode temperature of ≈600°C are reported. A maximum laser output of about 0.3 mW was found at spacings of 5.0–6.0 mm and about 3.0 Torr. A visible shift in the discharge color from pink to orange as the voltage is reduced is tentatively explained in terms of an increasing importance of direct neon excitation at lower voltages. The effect of this on the laser signal and threshold is discussed.