A method and system are presented for use in recording/reading data from an array of data units within a three-dimensional storage medium. Exciting radiation is provided in the form of first and second light beams of first and second different wavelengths, respectively. The first and second light beams are concurrently directed and focusing onto desirably distanced from each other sites in the medium and excited light of a third wavelength coming from the excited site is collected to form an excited light beam to be directed towards a detector assembly, while correcting for chromatic and spherical aberrations of the light focusing and collection. This focusing/collection is sequentially repeated for successive sites in the medium with varying depth of focus.
