Reduction of lasing threshold by protecting gas and the structure dependent visual lasing mode of various CdS microstructures

The lasing behaviours of semiconductor micro/nanostructures were studied in different gaseous surroundings, and the lasing threshold of the nanowire was reduced from 10.5 MW/cm² in air to 9.82 MW/cm², 8.25 MW/cm² and 7.22 MW/cm² in Ar, N₂ and He environment, respectively. It is attributed to the transient polarization of molecular gas. Moreover, the narrow-bandwidth lasing from the junction of a comb-like microstructure is hard to realize compared to that in nanowire and nanobelt due to the absence of good resonance cavities, and the only amplified spontaneous emission was observed by the ICCD dynamic images of the photoluminescence. The PL spectra and ICCD dynamic images, as well as lifetime measurement, prove the occurrence of lasing in nanowires and nanobelts with the pumping power increase, which should originate from the exciton-electron scattering and the formation of EHP, respectively. The whispering-gallery-mode lasing in nanowire and Fabry-Perot-Mode lasing in nanobelt were intuitively demonstrated by the ICCD images. The results provide one route to reduce the lasing threshold by the gas protection.