Résumé
We demonstrate that the spin coherence relaxation of excitons can be measured in a three-beam four-wave mixing experiment in the chi((3)) regime, using a sequence of contracircularly polarized pulses. In contrast to other techniques like Faraday rotation measurement, our method allows one to access spin coherence without applying an external magnetic field. The superposition of opposite spin states (exciton-polariton spin coherence) is then probed in a nondegenerate configuration at the biexciton-exciton transition. Measurements are performed on a bulk CuCl platelet. The polariton effect is taken into account by modeling the propagation of the pulses. The exciton-polariton spin coherence time is demonstrated to be mainly determined by their spin lifetime.