A double longitudinal mode He-Ne laser with frequency stabilization is proposed. Compared with general methods, such
as Lamb dip, Zeeman splitting and molecule saturation absorption method, this design has some advantages, such as no
piezocrystal or magnetic field, a short frequency-stabilized time, lower cost, and higher frequency stability and
reproducibility. The metal wire is uniformly wrapped on the discharge tube of the laser. When the metal wire is heated
up, the resonant cavity changes with the temperature field around the discharge tube to make the frequency of the laser
to be tuned. The polarizations of the two longitudinal modes from the laser must be orthogonal. The parallelly polarized
light and the vertically polarized light compete with each other, i. e., the parallelly polarized light generates a larger
output power, while, the vertically polarized light correspondingly generates a smaller one, but an equal value is found at
the reference frequencies by automatically adjusting the length of the resonant cavity, due to change of the temperature
in the discharge tube. Consequently the frequencies of the laser are stabilized. In my experiment, an intracavity He-Ne
laser whose length of the resonant cavity is larger than 50mm and smaller than 300mm is selected for the double
longitudinal-mode laser. Influence factors of frequency stability of this laser is only change of the length of the resonant
cavity. The laser includes three stages: mode hopping, transition stage, and modes stability from startup to laser stability.
When this laser is in modes stability, the waveform of heating metal wire is observed to a pulse whose duty is almost
50%, and thermal balances of the resonant cavity mainly rely on discharge tube.