Fig. 2: Emission dynamics of random laser action for the HMM structure.

a–c The emission spectra of the PNCs on top of the HMM1, HMM2, and glass substrate, respectively. The emission spectra were measured at four kinds of pumping power density, high power density (0.31 kW cm⁻²), medium power density (0.23–0.29 kW cm⁻²), and low power density (0.13–0.20 kW cm⁻²) to realize the power-dependent emission spectra as a critical realization of the laser action. All the measured emission spectra were excited using a 374 nm pulsed diode laser. The insets are the corresponding lifetime measurements. d The maximum lasing peak emission intensity as a function of pumping energy density. The slow rising slope is the amplified spontaneous emission, the drastic slope is the stimulated emission, and the intersection represents the lasing threshold (hollow circle). For the HMM1 (HMM2 and glass substrate), the lasing threshold is 0.27 (0.22 and 0.30) kW cm⁻². Error bars are the standard deviation of spectra fluctuation of random laser action from 15 datasets. e The corresponding full width at half maximum (FWHM) and f the averaged lifetime as a function of pumping energy density.