Pulsed Laser as a Continuous Particle Stream

Abstract: With the recently introduced particle interpretation of the double-slit experiment for light fields [Phys. Rev. Lett. 134, 13360 (2025)], all related interference phenomena can be reinterpreted in terms of light particle states that either couple (bright) or do not couple (dark) with detectors. Here, we apply this approach to multimode pulsed lasers, unifying the description of their generation inside optical cavities and propagation outside them, now relying solely on quantum mechanics, i.e., without invoking wave superposition to explain pulse shaping. Specifically, we demonstrate that multimode interference presents a dominance of particle dark states over the bright ones and mode-locked pulsed lasers consist of a continuous photon beam, with photons forming bright states during pulses and dark states in between. Additionally, we analyze mode-locked pulsed lasers, showing that the theoretical bright-to-dark state ratio matches the experimental pulse-to-interval duration ratio.