Fig. 4: Optical gain in type-(I + II) QDs.
From: Colloidal quantum dots enable tunable liquid-state lasers
a, TA spectra of type-(I + II) QDs (same sample as that in Figs. 2 and 3) presented as the excited-state absorption coefficient (α) for a pump–probe delay of 10 ps and for excitation levels 〈N〉 = 1.4–34.3 (190 fs, 2.4 eV pump pulses). α = α0 + Δα, where α0 is the ground-state absorption coefficient (unexcited sample) and Δα is the pump-induced absorption change. The optical gain appears as α < 0. b, TA dynamics yield optical gain lifetimes (τg) up to 3.0 ns. The gain dynamics of compact cg-QDs (τg,ccg) from another work17 are included for comparison (grey line).
