New J. Phys. 13, 093011 (2011)

Using two-pulse photon echoes to slow down light in an ensemble of cold atoms may allow photon storage with ultrawide bandwidths for optical information processing and memory. However, achieving these goals will require researchers to overcome issues of low photon retrieval efficiency and short storage times. Joonseong Hahn and Byoung Ham from Inha University in South Korea now claim to have observed a 15-fold improvement in photon echo efficiency using an optical locking scheme, which the authors call atom phase-controlled optical deshelving. The researchers used rare-earth Pr3+-doped Y2SiO5 housed in a liquid helium cryostat at ∼5 K. They controlled the characteristics of the light pulses by employing the acousto-optic modulated output from a ring-dye laser, together with digital delays and radiofrequency switching. Avalanche photodiodes for detecting the output light demonstrated the rephasing of two-pulse photon echoes and provided a measured storage (spin dephasing) time of around 9 μs. The researchers say that the storage time could be significantly extended by using optically dense media and external d.c. magnetic fields.