Utilizing light focusing by gas discharge medium for stabilization of emission power of He-Ne laser at wavelength of 6401 angstroms

Emission from an He-Ne laser operating in the lowest transverse mode at a wavelength of 6,401 A passes through a gas discharge cell and a stop which are positioned in series along the laser beam axis. A portion of the radiation is routed to a photodiode in a feedback loop by a semitransparent mirror. The photodiode output is amplified and fed to a discharge circuit of the gas discharge cell. The focusing properties of the discharge and the size of the laser beam spot in the diaphragm stop plane change as a function of the discharge current in the cell. The phase of the signal in the feedback loop is chosen so that an increase in laser power is accompanied by an increase in the emission spot size and a power decrease reduces the diameter of the laser beam. A methane cell is placed in the laser to suppress the 3.39 micrometer lasing. This scheme effectively suppressed output power fluctuations up to frequencies of about 30 KHz.