Persistent spectral hole burning [1] in conjunction with holography (PSHB) opens new prospects for high density optical information storage and processing. In the holographic approach, hole burning is carried out with two -crossed coherent laser beams which bleach out a narrow frequency domain hole in an inhomogeneously broadened absorption band recording, at the same time, a spatial holographic fringe pattern. During read out of the hologram diffraction from this spatial fringe pattern occurs, and a holographic image is reconstructed, reflecting the changes of the absorption coefficient and the refractive index introduced by the spectral hole [2].
A novel technique of recording holograms in spectral hole-burning systems has been developed. During hologram exposure, the frequency of narrow band laser light is `swept' over a frequency range, corresponding to a few homogeneous linewidths of the spectrally selective recording material. Simultaneously the phase of the hologram is controlled as a function of the frequency--the so called phase sweep function. Due to the phase reconstructing properties of holograms, this recording method programs the sample as a spectral amplitude and phase filter. This leads to interesting diffraction phenomena: plane swept holograms show strongly asymmetric signals in conjugated diffraction orders.
By utilizing giant Kerr nonlinearity obtained by electromagnetically induced transparency (EIT), tunable volume transmission holographic gratings for a weak probe field can be generated by means of a standing-wave signal field at low light levels in a four-level
N-type ultracold atomic ensemble. The induced grating can be characterized as a mixed volume holographic grating with a strong phase modulation accompanied by a weak amplitude modulation. Based on Kogelnik's coupled-wave theory in optical holography, we find that high diffraction efficiency (up to
85) and sensitive angular selectivity (up to $\ifmmode\pm\else\textpm\fi{}0.000149$ rad) can be achieved for the induced grating in the Bragg diffraction regime. And, both of them can be dynamically controlled by tuning the weak standing-wave signal field and the coupling field. Our study not only develops a fundamental understanding of volume diffraction effects in EIT media, but also provides a practical prototype of EIT-based holographic devices for all-optical classical and quantum information processing.