A list of ideal physical attributes for a holo-graphic storage medium may include the following:
• Recording mechanism – a large dynamic range
of optically induced, and preferably optically
erasable, refractive-index change (e.g., •n max •
10 •3 to 10 •2 ), negligible absorption;
Why refractive modulation rather than polarization?
• Sensitivity – responsive to (widely and cheaply
available) red wavelengths, an appreciable holo-graphic
writing sensitivity (e.g., on the order of
10 •2 cm 3 /J) requiring low recording powers;
With more powerful LD available, this is not as important?!
• Optical quality – suitable for casting in the form
of thick slabs with large surface areas (i.e., a
thick disk), high resolution (e.g., up to 5000 cy-cles/
mm), negligible scattering;
Maybe stackable sheets, or small distributed memories are the ticket?
• Stability – retain recorded data indefinitely over a
wide range of ambient (temperature, humidity,
etc.) conditions, show low fatigue over many
(e.g., millions of) write–read–erase cycles;
Maybe stabilities of greater then a few millisecs. and less then 15 sec. would be the best use?
• Volatility – a (simple) physical means of “fixing”
the recorded holograms so that they are not
weakened (or erased) by subsequent recording
and read-out beams;
Maybe ‘completely’ dynamic with NO! fixing would be best?
• Self-processing – no need for processing or de-veloping
of any kind (e.g., chemical, thermal,
magnetic, UV, IR, etc.) before or after recording;
and last but not least,
Maybe NOT self processing is the way to add fixing?
• Cost – material readily and cheaply available or
If the memory is designed into the microprocessor assembly and consumer amortization will handle the cost, why would ‘cheap’ be better?
As usual, with most people... 'agenda!' is paramount. NASA obviously has a ‘product view’ in mind and these are the attributes to fulfill that... but IT IS NOT TO SAY THAT everything they want, and are willing to pay to get...is the 'only way to go' to be of use to other people’s multimillion dollar cash cow dreams. Holograms, per se, are one of the most under used!, and under rated! 'practical solutions', ...even in their present! 'under developed' form.