Enhancing multi-photon induced excitonic emission of ZnO single crystals by shaping fs laser pulses

We report on the control of multi-photon excited emission of the ZnO exciton band via spectral phase modulation of the femtosecond excitation pulses. It was observed that the optimum spectral phase that enhances the exciton emission results in a pulse-train temporal profile, whose separation corresponds to an energy of 82 meV, which is close to the energy of LO phonon sidebands in ZnO emission. Such a result suggests that exciton–LO phonon coupling can be explored to coherently enhance the exciton emission in ZnO single crystals with respect to the defect luminescence band. (letter)