A new form of read out for high density read-only memory is presented
whereby a data density of 400 bits/mu m(2), corresponding to 256 Gbits
/in.(2), can be accessed at data rates in the tens of MHz range. The t
echnique is based on detecting the modulation in light scattering from
a sharp scattering object due to the dipole-dipole coupling between t
he probe and surface being scanned using a sensitive homodyne interfer
ometer. Theoretical considerations indicate that data densities in the
100 Tbits/in.(2) range could be accessed at data rates of 100 MHz usi
ng this technology. (C) 1997 American Institute of Physics.