Fig. 3: Origin of the ultrashort laser pulse doubling.

a Normalized transient absorption (TA) dynamics probed at the excitonic photobleaching peak (at 750 nm) of the high-dimensional (HD, n ≥ 5) perovskite QWs in the gain medium. Inset shows the fitted TA peak rising time as a function of pump fluence. The error bars represent the uncertainties of the fittings. b Simulated carrier recombination dynamics at different carrier funneling times and recombination rates in the perovskite MQWs gain medium. See Supplementary Note 1 and Supplementary Table 1 for detailed parameter values. c Normalized time-resolved photoluminescence (TRPL) decay curves for perovskite MQWs from low to high pump fluence following excitation at 400 nm (1 kHz, 50 fs). d Schematic illustration of the formation of double-pulsed stimulated emission (StE) by single fs laser pulse pumping via the fast and slow carrier funneling processes in MQWs.