Spectrum Broadening in Optical Frequency-Shifted Feedback of Microchip Laser

The influence of feedback level and shifted frequency on laser spectrum and power spectrum is investigated experimentally and theoretically. Due to optical frequency-shifted feedback, the spectrum of Nd:YVO
₄
microchip laser is expanded into one with multi equal-spaced sidebands around its initial central frequency. The detail of expanded spectrum depends on both the shifted frequency and relaxation oscillation frequency. Optical feedback level decides the possible maximum spectrum range. Nevertheless, the actual spectrum range depends on both the frequency shift and the feedback level. The power spectrum turns from simple to complex with the increase of feedback level when the shifted frequency is a constant. A rate-equation model with optical frequency-shifted feedback is built to interpret the experimental phenomena. The theoretical results accord with the experiments very well. This letter can help choose appropriate parameters for feedback interferometry systems and promote the accomplishment of optical frequency-shifted feedback diagram, which could be a guide for feedback interferometry applications.