Toward exploring noncontinuous-state dynamics based on pulse-modulated frequency-shifted laser feedback interferometry

An exhaustive study of the noncontinuous-state laser dynamics associated with the transient optical process is significant because it reveals the complex physical mechanisms and characteristics in nonlinear laser systems. In this study, in-depth theoretical interpretation and experimental verification of the noncontinuous-state dynamics in laser system are presented, based on developed pulse-modulated frequency-shifted laser feedback interferometry (LFI). By introducing external pulse modulation, we investigate the nonlinear time-of-flight dynamics and related photon behaviors evolution of the pulsed LFI system by observing the changes in effective interference time sequences for interference realization and attainable minimum feedback photon number of the signal under various modulated noncontinuous states. Implementation of the pulse-modulated LFI scheme should exceed the pulse overlapping time window limit of 1.93 μs to effectively extract and preserve the extracavity feedback photon information. Experiments reveal that the minimum feedback photon number of signals successfully measured by the pulsed LFI sensor is 0.067 feedback photons per Doppler cycle, exhibiting high sensitivity for extremely weak signal detection. Further, simultaneous measurement for velocity and distance of the moving object is performed to validate the feasibility and applicability of the pulsed LFI. The system can successfully achieve large-range simultaneous measurements within the velocity range of 73.5−612.6 mm /s, over a distance of 25.5 km. This work opens the way to unexplored frontiers of pulsed LFI to fill the research gap in noncontinuous laser dynamics in this field, showcasing diverse and wide-ranging applications in the realm of integrated sensing, remote monitoring, and positioning and navigation.