Restoration of the near-diffraction-limited response size at heterodyne detection of microholograms, distorted by spherical aberration.

Spherical aberrations (SAs) are an important factor in limiting the number of recording layers in a multilayer microholographic data storage scheme. This paper discusses the effect of the restoration of the response size, which makes it possible to decrease considerably the requirement of accuracy for the SA correction of the optical pickup system. The restoration occurs at the heterodyne detection of microholograms distorted by aberrations. The effect of restoring is demonstrated experimentally. A study of the dependence of the microholograms' lateral and longitudinal sizes on the medium depth in which they were formed was carried out. To measure the longitudinal size, a special material containing submicron microspheres was used. The size of the microhologram distorted by aberrations was then compared with the response size obtained at detection. In the last step, a conclusion about the restoration of the response size is made. The multilayer microholograms recording was carried out in iron-doped lithium niobate at a depth range from 70 to 520 μm. A mathematical model of the microholograms' recording-reading was developed. This model makes it possible to give a qualitative explanation of the processes leading to the restoration of the near-diffraction-limited response size.