Comparative Performance of Hollow-Cathode and Axial Plasma Helium-Neon Lasers
Final rept. 15 Dec 1971-15 Dec 1972
INFORMATION SYSTEMS MENLO PARK CA
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This report covers a 12 month, primarily experimental investigation of the comparative performance characteristics of slotted hollow-cathode and axial plasma positive column 6328A He-Ne lasers. The program included the evaluation of parameters that control power performance and culminated in the construction of a TEM mode power-optimized slotted hollow-cathode laser. The program was carried out in three main phases. First, a 15 mW TEM sub zero zero mode power-optimized axial plasma laser was constructed utilizing a 1-meter long folded confocal laser cavity. Second, a series of systematic parametric evaluations on the 6328A laser oscillation of He-Ne-slotted hollow-cathode discharges using various cathode diameters was carried out using the same type of laser cavity. Among the most important observations made in this phase were the inability, due to plasma expulsion from the cathode interior, to reach optimal operating pressure for maximum 6328A output, consequently the power output and efficiency were lower than that of the 6328A axial plasma laser and a comparatively high optimal HeNe mixture ratio. Third, on the basis of the parametric evaluations, a TEM sub zero zero mode power-optimized slotted hollow- cathode laser was constructed using a 1-meter long folded-confocal laser cavity. The performance characteristics of this laser, were maximum TEM sub zero zero mode output power of 2 mW, optimal total operating pressure of 4 Torr, a HeNe mixture ratio of 201 and nominal discharge current and tube voltage of 400 mA and 220 volts respectively.
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