Slow have recently received a large interest, both from the fundamental point of view and for potential applications, in pulse buffering/multiplexing, high sensitivity interferometers, precision metrology and optical sensing. After the early achievements obtained by exploiting electromagnetically induced transparency in ultracold atoms, slow-light has been realized at room temperature by using a mechanism called coherent population oscillation in solid crystals and, nowadays, different methods to realize slow and fast-light are currently employed. Among them, the processes of nonlinear wave mixing offer the advantage of large and tunable dispersion properties, which can be used to obtain controllable group velocities in small-sized experiments. These properties have been exploited in photorefractive crystals, in optical fibers through stimulated Brillouin scattering and in semiconductor structures.
Recently, we have shown that by performing two-wave mixing experiments in a liquid crystal light-valve, LCLV, we are able to obtain fast and slow-light down to group velocities as slow as a few tenths of mm/s. In the LCLV the wave-mixing process is characterized by the presence of multiple-order output beams, each experiencing a different group delay. The large transverse size of the LCLV allows also delaying whole images, a property that can be exploited for optical storage and wavefront sensing.

The large group delay provided by the beam coupling in the light-valve corresponds to a large group index, which, on the other hand, is associated to a narrow frequency bandwidth of the two-wave-mixing gain. These properties can be used to realize applications in high precision interferometry and adaptive holography, with systems that allows the detection of subpicometer displacements.