Long-lived conjugate optical echo in a crystal

Observation of a long-lived multiple optical echo

Inverted long-duration optical echo in a crystal

Accumulated long-lived photon echoes and optical memory in LaF3:Pr3+ crystals

An accumulated long-lived light echo and optical memory

Optical memory based on long-lived photon echo (review)

Long-lived stimulated photon echo in optically thick van vleck paramagnets