Highly multimode storage in a crystal

We experimentally demonstrate the storage of 1060 temporal modes onto a thulium-doped crystal using an atomic frequency comb (AFC). The comb covers 0.93 GHz defining the storage bandwidth. As compared to previous AFC preparation methods (pulse sequences, i.e. amplitude modulation), we only use frequency modulation to produce the desired optical pumping spectrum. To ensure an accurate spectrally selective optical pumping, the frequency-modulated laser is self-locked on the atomic comb. Our approach is general and should be applicable to a wide range of rare-earth-doped materials in the context of multimode quantum memory.