Optical feedback effects in orthogonally polarized dual frequency He–Ne laser

We introduce the multiple-beam interference into Lamb’s semi-classical gas-laser theory to analyze the optical feedback effects in orthogonally polarized dual frequency He–Ne laser. The feedback order N which determines optical feedback level and the beam order back into the cavity is defined. The intensities of o-light and e-light are leaning and alternate (N = 1). The whole intensity of the laser branches off (N = 2) with different reflectivity of the feedback mirror. Obvious humpback on the opposite side of the two orthogonally polarized frequencies’ curves is discovered (N = ∞). These results are used to advance the development of dual frequency self-mixing interferometer.