Transverse dynamical response of laser frequency-shifted feedback with mode mismatch

Abstract

The transverse mode mismatch between the echo wave and optical fields in the laser cavity substantially impacts the responses of the laser frequency-shifted feedback (LFSF) system. This mismatch widely exists in experiments, which limits the detection sensitivity and degrades the signal-to-noise ratio. However, current research on the dynamic response of LFSF has predominantly concentrated on longitudinal modes and intensity modulation, with a lack of quantitative analysis regarding the dynamic response of the transverse modes. In this paper, we establish a transverse dynamical response model of LFSF considering the mode-mismatch. A calculation method of the effective reflectivity (ER) and mode-matching factor (MMF) is presented by decomposing the echo wave to the eigenmodes of the laser. The theoretical model is highly consistent with the experimental data. Finally, with this transverse dynamical response model, we develop a simple scheme to calibrate the effective reflectivity of scattering surfaces by employing a cat's eye retroreflector. Overall, this paper provides a detailed demonstration of the mismatch, which promises an effective theoretical basis to make full use of the high sensitivity of LFSF and apply it over a long distance.