Dynamic response and relaxation oscillations in random lasers

TLDR

We investigate the dynamic response of random lasers using picosecond optical pumping. The study employs picosecond optical pumping together with semiclassical laser theory and finite‑difference time‑domain simulations to probe random laser dynamics. The experiments reveal that random lasers turn on in under 100 ps, emit shortened pulses above threshold, and exhibit mode‑dependent dynamics—including staggered onset, varying lifetimes, frequency shifts, and relaxation oscillations.

Abstract

We experimentally investigate the dynamic response of random lasers using picosecond optical pumping. It is found that the turn-on time of a random laser is less than 100 ps. Above the lasing threshold, the emission pulse is shortened dramatically. The dynamics of each individual lasing mode is different. Lasing starts and gets to a maximum value at different times. In addition, lasing in different modes lasts for different periods of time, and the frequency of some lasing modes also shifts with time. Relaxation oscillations of lasing modes are observed for a random laser. The theoretical simulations based on the semiclassical laser theory and finite different time domain reproduce most of the experimental observations and provide an understanding of the dynamic response of a random laser.