Multiphoton absorption pumped ultraviolet stimulated emission from ZnO microtubes

We report observation of stimulated emission from ZnO microtubes pumped by multiphoton absorption using intense femtosecond pulses at wavelength around 800 nm. Band edge emission, together with second harmonic generation, was observed and several stimulated emission peaks with linewidths of 0.5-0.7 nm appeared at high excitation fluence. The stimulated emission from the microtubes were attributed to the excitonic effect at intermediate fluence (50-100 mJ/cm(2)) and electron-hole plasma at high fluence (>100 mJ/cm(2)), respectively. Possible Fabry-Perot cavity effects were also discussed. (C) 2007 American Institute of Physics.