Ultralong ZnO microrods with a perfect hexagonal cross section were synthesized on a large scale by the vapour phase transport method and were employed as a whispering-gallery mode (WGM) cavity to realize optical resonance and lasing. An individual ZnO microrod was selected to investigate the multiphoton absorption-induced optical behaviours based on the enhancement of the nonlinear optical interaction in the WGM cavity. Three-photon absorption-induced UV lasing, second-harmonic generation and defect-related visible emission simultaneously present distinct WGMs under the excitation of femtosecond laser pulses at 1200 nm. When the pump laser was changed to 1240 nm, four-photon absorption-induced WGM lasing was observed. The characteristics and generation process of the above resonant signals were investigated in detail.
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