Coherence analysis of laser pulses based on an external cavity circulation

By constructing an external circulating cavity to provide sufficient delay that equals a multiple of pulse repetition time, a method with a fixed experimental configuration is proposed to measure the coherence length of both single-frequency and microwave-modulated optical pulses. This method can accurately determine the number of coherent pulses as well as distinguish the coherence states: complete coherence, partial coherence and complete incoherence. In addition, all desired coherence phenomena are obtained by one-time measurement, avoiding other operations like frequent fiber-cutting or devices-reconnection in previous methods. Simulation results show that the coherence length of the dual-frequency laser is periodically extended by the reciprocal of the frequency difference, and the random jitter of pulse propagation time would result in obvious measurement errors via perturbing coherence status.