Fig. 3. ASE, VSL, and optical gain stability characterizations of the CQWs having four monolayers of shell.

a Pump-dependent ASE spectra at 〈N_o〉 = 0.63, 0.84, and 1.10. The position of spontaneous emission (SP), ASE and X-band are marked by solid black line. b Integrated PL intensity of ASE spectra as a function of the pump fluence and the corresponding average number of excitons per NPL (〈N_o〉). c Spectral analysis of ASE along with absorbance (dashed blue line) of the lowest excitonic energy state with respect to the 〈N_o〉. The position of 1_hh–1_e excitonic transition and ASE peak are marked by dark dashed lines. d Pump-dependent net peak modal gain coefficient (symbols) at the ASE peak position (λ_ASE = 647 nm). The solid line is the numerical fitting to the experimental data, indicating a saturation fluence at ~920 μJ cm⁻². The highest G reaches 1960 ± 100 cm⁻¹ at 746 μJ cm⁻² pump fluence. Error bars in this figure are a result of uncertainty of the fitting parameter in the variable stripe length measurement presented in Supplementary Fig. 7 as exemplary cases. e Pump-dependent ASE intensity as a function of the pump laser shot at 〈N_o〉 = 1.36. Error bars in this figure comes from the fluctuations in the ASE intensity between different measurements. The light amplification is highly stable in these engineered CQWs even for 9.5 h of continuous excitation.