Measurements of exciton–polariton dynamics in ZnO by using nonlinear spectroscopic techniques

We have studied the exciton–polariton dynamics in a c-face bulk ZnO crystal grown by the seeded vapor transport method. We have performed two-pulse spectrally resolved four-wave mixing (SR-FWM) and three-pulse SR-FWM at image K. In two-pulse FWM experiment, obtained FWM signals showed the fast dephasing which has been attributed to the strong polariton dispersion of the upper polariton of image exciton. On the other hand, in three-pulse FWM experiment, the signal decay shows the free exciton population relaxation. Observed FWM signal has decayed with time constant image12 ps which may represent exciton–polariton lifetime.