Modulation method for reducing long-term drift of the emission frequency of an He–Ne laser (λ = 0.63 μm) generating two orthogonally polarized electromagnetic waves

Theoretical and experimental investigations were made of the principal physical factors responsible for a long-term drift of the frequency of the radiation generated in a stabilized two-frequency He–Ne laser with internal mirrors, emitting two orthogonally polarized electromagnetic waves. When zero difference between the intensities was controlled by a modulation method and the frequency was set before each measurement, a long-term (over a period of a year) frequency drift did not exceed 10 ^{– 8}, but in the absence of such control the drift could reach 5 X 10 ^{– 8}.