Harmonic readout of a volume hologram in an optically reversible medium

Claim 2

In a method of recording and retrieving information stored in a reversible optical storage medium as a volume hologram by projecting a light beam thereon, the reversible storage medium being of a material whose optical properties change from one condition to a second condition when exposed to a light beam of a given frequency and change back to the one condition when subsequently exposed to a light beam of a second frequency and whose optical properties do not change when exposed to a light beam of a third frequency the improvement comprising recording said information as a volume hologram in a material having said third frequency as a harmonic of said given frequency with a light beam of said given frequency, providing a reading light beam having said third frequency which is the harmonic of the frequency of the light beam utilized to record the information as a volume hologram on the storage media, and projecting the reading light beam onto the storage medium to retrieve the information contained in the volume hologram without adversely causing optical changes in the storage medium.

Claim 3

In a method according to claim 1, wherein the reading light beam is provided by passing the recording light beam through a harmonic generator utilizing a non-linear optical material to obtain the reading light beam having a harmonic frequency of the frequency of the recording light beam.

Claim 4

In a method according to claim 2, when the passing of the recording light beam through the harmonic generator produces a beam of light of the recording frequency and a reading light beam having a harmonic frequency of the frequency of the recording beam, and which method further includes the step of selectively projecting the recording light beam and the reading light beam on the storage medium to selectively record information thereon and to retrieve information therefrom.

Claim 5

In an apparatus for recording and retrieving information recorded in a volume hologram on a reversible optical storage medium by a beam of light having a recording frequency, the storage medium being of a material whose optical properties change from one condition to another condition when the material is exposed by a light beam of a given frequency and changed back to the one condition when subsequently exposed to a light beam of a second frequency and whose optical properties do not change when exposed to a light beam of a third frequency, said apparatus having a means for projecting a light beam on the storage medium, the improvement comprising said means for projecting including means for recording said information as a volume hologram comprising a source of light at said given frequency for use as a recording light beam, and means for generating a reading light beam having said third frequency which is a harmonic of the given frequency of the recording light beam so that as the reading light beam is projected on the storage medium the information contained in the volume hologram is retrieved without causing optical changes in the storage medium.

Claim 6

In an apparatus for recording and retrieving information recorded in a volume hologram on a reversible optical storage medium by a beam of light having a recording frequency, the storage medium being of a material whose optical properties change from one condition to another condition when the material is exposed by a light beam of a given frequency and changed back to the one condition when subsequently exposed to a light beam of a second frequency and whose optical properties do not change when exposed to a light beam of a third frequency, said apparatus having a means for projecting a light beam on the storage medium, the improvement comprising said means for projecting including means for recording said information as a volume hologram comprising a source of light at said given frequency for use as a recording light beam, and means for generating a reading light beam having said third frequency which is a harmonic of the given frequency of the recording light beam so that as the reading light beam is projected on the storage medium the information contained in the volume hologram is retrieved without causing optical changes in the storage medium.

Claim 7

In an apparatus according to claim 4, wherein said means for generating a reading light beam includes a harmonic generator comprising a non-linear optical medium for producing a reading light beam having a frequency which is a harmonic of the frequency of a recording light beam.

Claim 8

In an apparatus according to claim 5, wherein the harmonic generator produces light beams having the frequency of the recording light beam and light beams having the frequency of the reading light beam and wherein said means of projecting further include means for selectively projecting the recording light beam and the reading light beam on the storage medium to selectively record information thereon and to selectively read information recorded thereon.

Claim 9

In an apparatus according to claim 6, wherein the light source produces a light beam having said second frequency for utilization as an erasing beam of light and wherein the means for selectively projecting is capable of selectively projecting the erasing beam of light on the storage medium for erasing information recorded thereon.