Three-dimensional optical memory

A memory apparatus for storing binary information in a three-dimensional volume of an active medium sensitive to radiation of an energy at least equal to a first threshold energy level so as to change from a first to a second isomeric form, the memory apparatus comprising:

• means for directing radiation of a first energy level, less than the first threshold energy level, to a selected portion of the active medium in order to excite this selected portion of the medium to a virtual state;
• and
• means for directing radiation of a second energy level, also less than the first threshold energy level, to selected parts of the selected portion of the active medium while this selected portion of the medium is in its virtual state;
• wherein the combined energies of the first energy level radiation and the second energy level radiation are at least equal to the first threshold energy level;
• wherein the means for directing radiation of the first energy level and the means for directing radiation of the second energy level jointly cause the selected parts of the selected portion to change from their first to their second isomeric form by process of plural-photon absorption;
• wherein the selected, changed, parts of the selected portion of the active medium and the remaining, unchanged, parts of this same selected portion of the active medium constitute binary-stated information.

A method of reading and writing an active medium with binary information comprising:

• spatially and temporally simultaneously illuminating by intersection of a first pair of radiation beams a selected region of a volume of active medium to cause, by process of two-photon absorption, a change in the active medium at the intersection region from a first to a second isomeric form,
• wherein at least one of the first pair of radiation beams passes through an additional volume of active medium not at the intersection region and is insufficient to cause any change of the isomeric molecular form of this additional volume of active medium;
• and
• subsequently spatially and temporally simultaneously illuminating by intersection of a second pair of radiation beams the active medium at the intersection region to cause, by process of two-photon excitation, the fluorescence of the active medium at the intersection region,
• wherein at least one of the second two radiation beams passes through an additional volume of the active medium not at the intersection region and is individually insufficient to cause any fluorescence of this additional volume of active medium.

An apparatus for employing a one-dimensional inhomogeneity pattern upon a line within a physical body of material, the apparatus comprising:

• a three-dimensional body of radiation-sensitive active material exhibiting at separate times at least a first and a second substantially stable isomeric forms and responsive to sufficiently energetic radiation energy to change between such forms;
• means for providing first-frequency radiation to selected discrete regions on a first plane within the three-dimensional body, the first-frequency radiation being individually insufficiently energetic so as to induce the material to change from its first to its second isomeric form;
• means for providing second-frequency radiation to selected discrete regions on a second plane intersecting the first plane along a line within the three-dimensional body, the second-frequency radiation being individually insufficiently energetic so as to induce the material to change from its first to its second isomeric form;
• wherein the first-frequency radiation and the second-frequency radiation temporally simultaneously energize discrete regions along a line within the three-dimensional body of material, the coinciding first-frequency radiation and the second-frequency radiation being jointly sufficiently energetic so as to excite the material at these discrete regions by process of two-photon absorption to change from its first to its second isomeric form;
• wherein other discrete regions of the three-dimensional body of material that are not along the line are not changed in isomeric molecular form.

A writable and readable binary memory, comprising:

• a photochromic material capable of exhibiting a first and a second substantially stable isomeric form, said material absorbing in its first form light of a first energy level in order to isomerize to its second stable isomeric form and thereafter tending to remain in this second stable isomeric form, said material absorbing in its second isomeric form light of a second energy level in order to fluoresce while remaining in its second isomeric form;
• means for selectively providing and directing onto the photochromic material a first-frequency light, lower in energy level than either of the first and the second energy levels, the first-frequency light being unable individually to cause either the isomerization or the fluorescence of the photochromic material;
• means for selectively providing and directing onto the photochromic material at the first time, a second-frequency light, lower in energy level than either of the first and the second energy levels, said second-frequency light being unable individually to cause either the isomerization or the fluorescence of the photochromic material;
• wherein the first-frequency and the second-frequency light together cause, by process of two-photon absorption, the isomerization of a photochromic material that is in its first isomeric form to its second isomeric form, or the fluorescence of the photochromic material that is in its second isomeric form;
• means for selectively providing and directing onto a photochromic material at a second time, a third-frequency light, lower in energy level than either of the first energy level and the second energy level, the third-frequency light being unable individually to cause either the isomerization or the fluorescence of the photochromic material;
• means for selectively providing and directing onto the photochromic material at the second time a fourth-frequency light, lower in energy level than either of the first energy level and the second energy level, said fourth-frequency light being unable individually to cause either the isomerization or the fluorescence of the photochromic material;
• wherein the third-frequency and the fourth-frequency light together cause, by process of two-photon absorption, the fluorescence of the photochromic material when it is in its second isomeric form, but cause no change in the photochromic material when it is in its first isomeric form.

For use in a method of producing a three-dimensional inhomogeneity pattern in a volume of material by selectively radiating the material with directed beams of electromagnetic radiation, a material consisting essentially of:

• an active medium
• capable of maintaining a relatively stable shape containable within a volume,
• substantially transparent to electromagnetic radiation below a threshold energy level,
• responsive to energy level changes resultant from plural-photon virtual absorption at selected locations within the volume so as to change from a first molecular structure to another, second, inhomogeneous and substantially persistent molecular structure at these selected locations, and
• substantially persistent at the selected locations after change of molecular structure so as to constitute, and so as to preserve, an inhomogeneity pattern at these selected locations.

A method of forming a substantially persistent three-dimensional shape comprising:

• containing a volume of a medium reactive to electromagnetic radiation;
• first-illuminating with a first beam of electromagnetic radiation selected locations within the medium, the first beam being insufficiently energetic so as to cause a change in the medium through which it passes;
• second-illuminating with a second beam of electromagnetic radiation at least some of the selected locations within the medium, the second beam being insufficiently energetic so as to cause a change in the medium through which it passes, simultaneously that these some selected locations are illuminated by the first beam;
• therein by the simultaneous first-illuminating and second-illuminating causing by a two-photon absorption process at these some selected locations the medium to change to a different isomeric molecular form, the some selected locations collectively forming a substantially persistent three-dimensional shape.

A method for generating a substantially persistent three-dimensional inhomogeneity pattern in a volume of medium in response to energy level changes within such medium stimulated by directed electromagnetic energy input, the method comprising:

• illuminating with a first beam of electromagnetic radiation first selected regions within a volume of medium, the first beam being insufficiently energetic so as to cause a change in the medium through which it passes substantially unreflected and undispersed and unabsorbed;
• illuminating with a second beam of electromagnetic radiation second selected regions within the volume of medium, the second beam being insufficiently energetic so as to cause a change in the medium through which it passes substantially unreflected and undispersed and unabsorbed;
• wherein at least some of the second selected regions are identical to some of the first selected regions and are illuminated by the first and the second beam simultaneously;
• wherein the identical regions are responsive to this simultaneously illuminating so as to change by process of two-photon absorption from one isomeric molecular form to another, substantially persistent, molecular form that is inhomogeneous with the first molecular form;
• wherein the simultaneously-illuminated inhomogeneous-molecular-form substantially-persistent regions collectively form a three-dimensional pattern.

A method of generating a visually perceptible three-dimensional image comprising:

• containing a volume of substantially visually transparent medium capable of maintaining a relatively stable shape;
• illuminating with a first beam of electromagnetic radiation selected regions within the medium, the first beam being insufficiently energetic so as to cause a change in the medium through which it passes substantially unreflected and undispersed;
• illuminating with a second beam of electromagnetic radiation at least some of the selected regions within the medium, this second beam being insufficiently energetic so as to cause a change in the medium through which it passes substantially unreflected and undispersed, simultaneously that these some selected regions are illuminated by the first beam;
• therein to cause by process of two-photon absorption at these some selected regions the medium to change from the substantially transparent to a substantially opaque molecular form;
• wherein the some selected regions collectively forming a visually perceptible three-dimensional image.