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Amplitude and phase modulation of optical feedback in a-cut Nd:YVO4 laser with a birefringent external cavity

Considering only the self-mixing interference taking place, the modulation effect of optical feedback in a single polarization a-cut Nd:YVO4 laser is presented. The output intensity of the laser with anisotropic gain medium is modulated with a wave plate (WP) in the external cavity. The rotation orientation and phase retardation of the WP regularly determinate the amplitude and phase of laser intensity fringe, because the feedback light component at the same polarization direction as the output laser can interact with the light field in the cavity. The corresponding theoretical model is established and the windowed Fourier transform method is utilized to quantitatively explain this phenomenon. By introducing the amplitude and phase modulation coefficients, comparisons of experimental results with simulation analysis show good consistency.