Abstract: A unique method for recording, reading and erasing data bits in a data storage device is described. Using extended scanning tunneling microscopy (STM) techniques, a tunneling electron current by resistive heating selectively melts discrete areas of a state-transformable film; then heat is dissipated rapidly, writing data bits by changing the film in said areas from a first state to a second state wherein an electronic property, such as conductance, work function or band gap, in said areas is changed.Again, using extended STM techniques, the effect of this changed electronic property of said film on the tunneling current is measured for reading the written data bits. Minimizing the effect of blemishes on the material is effected, during operation in STM constant current mode by measuring dI/dV or dI/ds, and during operation in STM variable current (constant gap) mode by measuring (dI/dV)/I or (dI/ds)/I.

Abstract: Direct overwrite of data on magneto-optic medium is described. Old data is erased and new data is written during a single rotation of the media in a data storage system which includes a resonant coil for producing a high frequency alternating magnetic field interacting with laser pulses having a duration equal to a small fraction of the period of the magnetic field. Variable-length magnetic domains are formed by overlapping circular magnetic domains to provide pulse width modulation (PWM) encoding of data.

Abstract: A process for accessing disk tracks in an optical storage disk using a laser beam passed through an acousto-optic deflector which generates an undeflected beam and at least one deflected beam both of which are focussed on the surface of the disk. The deflected beam is used to read or write data and the undeflected beam is used to follow a servoing structure on the disk.

Abstract: A method and apparatus for imaging objects utilizing acoustic waves at frequencies above 4.2 Ghz and up to 8 Ghz wherein the transducer and the object imaged by waves or beams from the transducer are both at a temperature no greater 0.2.degree. K. The transducer is driven by pulses generated by a short pulse generator which are stretched and coded by a dispersive filter and inductively coupled to a low temperature coupler to be use to drive the transducer. The frequency returns are carried by the same bidirectional coupler to a low noise amplifier. Both the low noise amplifier and bidirectional coupler are maintained at a temperature of less than 4.2.degree. K. The output of the amplifier is then coupled to a dispersive filter which responds the coding in the first dispersive filter to decode the information and reconstruct the signal. Subsurface defects are detected by heating the object while it is inspected by the acoustic transducer.