Frequency-upconverted whispering-gallery-mode lasing in ZnO hexagonal nanodisks

Low threshold, frequency-upconverted lasing in the two-photon absorption regime was observed in hexagonal ZnO nanodisks. Upon near-IR excitation, the ZnO nanodisk resonators produced UV laser emission with a remarkably low threshold (approximately 1 mJ/cm(2)) as well as a resolved lasing linewidth of approximately 0.1 nm. Modal analysis and far-field photoluminescence imaging of the nanolasers have suggested the dominance of whispering-gallery modes in the two-photon pumped microcavity lasing process.