Laser dynamics under frequency-shifted optical feedback with random phase

The rate-equation model for a semiconductor laser under optical feedback is a useful tool for studying complex laser dynamics. Optical feedback from scatterers suspended in fluid flow and rough bodies in motion consists of many, spectrally close, Doppler-shifted frequency components with random phase. How this type of feedback is included in the well-established Lang and Kobayashi model is clarified, resulting in simulated results that agree well with the experiment in both time and frequency domains. Equipped with this model, the dynamic effects of laser feedback systems measuring flow or rough targets in motion may be studied numerically.