Adaptive holographic interferometry (AHI)

The main objective of adaptive interferometry is to detect frequency phase modulations of optical beams with complex wavefronts, such as speckle beams, characterized by low frequency noise fluctuations as given by environmental disturbances when the beam passes through the atmosphere, or turbid media or biological tissues. Adaptive holography addresses the problems related to these types of measurements by using an interferometer scheme where the signal beam, carrying the phase modulations, is made to interfere with a reference beam, thus producing an adaptive hologram. This last one is made by a nonlinear medium able to provide a self-reconīŦgurable index of refraction.
The slow-light phenomenon, usually induced by a rapid change of the refractive index, is associated to a narrow frequency bandwidth of a resonant process. In the LCLV slow-light occurs through a two-wave mixing process, which is characterized by a gain profile with a very narrow frequency bandwidth.

Two-wave-mixing in the LCLV provides both a good sensitivity and a narrow frequency bandwidth, and, can, therefore, be efficiently used to realize an AHI system. A piezo-mirror is used to produce small displacements of the signal beam. We have shown that the AHI detection is linear for small displacements and that mirror displacements as small as 10E-13 m are easily detected with our LCLV-based system. The system can also work with complex wavefronts.