Random Lasing in ZnO Nanopowders Based on Multiphoton Absorption for Ultrafast Upconversion Application

This study reports ultraviolet picosecond random lasing (RL) based on multiphoton absorption in zinc oxide (ZnO) nanopowders with a mean size of ∼100 nm under femtosecond optical excitation. Upconversion random lasing is achieved with an excitation wavelength increasing from 600 to 1800 nm, corresponding to a five-photon excitation. The RL threshold has a slight positive relationship with excitation wavelength, except for a significant increase with four-photon excitation at 1200-1300 nm, demonstrating promising upconversion lasing properties of ZnO nanopowders. A remarkably lower RL threshold is observed at long excitation wavelengths ranging from 1500 to 1800 nm than that for four-photon pumping (1200-1300 nm) processes. Defect states in ZnO are suggested to be the reason that results in the excitation wavelength dependence of random lasing. Transient RL characteristics are investigated using time-resolved photoluminescence measurements, with the RL pulse delay time and pulse width observed to decrease with increasing excitation power, demonstrating typical gain-switching lasing characteristics. The 2.6 ps ultrashort pulse width indicates potential for ZnO in ultrafast upconversion random lasing devices.