Frequency stabilization of ambience-isolated internal-mirror He–Ne lasers by thermoelectric-cooling thermal compensation

An approach for frequency stabilization of anambience-isolated internal-mirror He–Ne laser (632.8 nm)utilizing temperature control of the laser tube with Peltierthermoelectric coolers is demonstrated. Measurementsindicate that there are an optimal temperature (23 ̊ C) andan optimal discharge current (5.5 mA) of laser tube forwhich the laser light power is separately maximized. Toprevent the effect of fluctuation of discharge current on thelaser stability, an adjustable current source is designed andfabricated so that the current is set to be optimal(5.50 ± 0.01 mA). To isolate the laser tube from theenvironment, the laser metallic box connected to two Peltierthermoelectric coolers is surrounded by two thermaland acoustic insulator shells. The laser has two longitudinalmodes very often. Any change in the frequency of longitudinalmodes at the optimal temperature is monitored bysampling the difference of longitudinal modes’ intensities.Therefore, using a feedback mechanism, the current ofthermoelectric coolers is so controlled that the frequency ofmodes stays constant on the gain profile of the laser. Thefrequency stability is measured equal to 1.17 x 10(-9)(~2700x) for less than 1 min and 2.57 x 10(-9)(~1200x) for more than 1 h.