Resolving the temporal dynamics of mode-locked laser with single-shot time-microscope

TL;DR

This paper introduces a high-resolution single-shot time-microscope using the time-lens technique with a Raman amplifier, enabling real-time observation of ultrafast laser pulse dynamics and revealing previously unobserved winding behavior.

Contribution

The study develops a novel ultrafast single-shot time-microscope with high temporal magnification, allowing detailed real-time analysis of mode-locked laser dynamics and uncovering new oscillation phenomena.

Findings

Revealed the winding behavior in mode-locked lasers.

Linked winding behavior to gain fluctuations and Q-switching.

Enabled observation of ~1.8×10^4 pulses in real-time.

Abstract

Mode-locked lasers, which produce ultrashort pulses in the picosecond and femtosecond range, have enabled some of the most precise measurements. However, despite significant recent progress, resolving the temporal behavior of their short pulses is still a challenge. State-of-the-art oscilloscopes with tens of picosecond resolution prevent time-resolved observations in mode-locked lasers and limit the real-time pulse evolution tracking of ultrafast lasers. Here, using the time-lens technique with a Raman amplifier, we implement an ultrafast single-shot time-microscope (TM) with a high temporal magnification factor of 355 and a time measurement window of 1 millisecond that contains ~1.8*10^4 consecutive pulses. We use this TM to characterize the temporal evolution of mode-locked lasers and reveal a temporal sideway oscillation (winding) behavior, a previously unobserved feature of lasers in both theory and experiment. Our experimental observations confirm that the winding behavior is an essential feature in the operation of mode-locked lasers. We theoretically and experimentally found that the winding characteristic evolution originates from gain-induced fluctuations for relatively high gain energies, while Q-switched modulations being the main cause for lower energies. Our findings based on advanced real-time measurements open up new insights into ultrafast and transient optics and may impact future laser designs, modern ultrafast diagnostics, and influence progress in nonlinear optics in general.