Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties

Definitions

• the present invention relates to the coherent interaction of optical radiation beams with ions or molecules in solids, and to the choice of propagation direction and light polarization relative to the crystal symmetry axes of the solid, and more particularly to optimize the optical-electronic interaction effects in materials with generalized crystal symmetry.
• optical-electronic applications are based on the coherent interaction of optical radiation beams or fields with ion-doped or molecular crystals of various types; these interactions include optical coherent transients, spectral hole burning, and spatial-spectral holography (also called time- and space-domain holography) .
• Devices based on these concepts are used in optical data storage, real-time optical signal processing, quantum computers, and other coherent computers where the coherent interaction of multiple radiation beams is enhanced, enhanced data erasure in coherent computers, and optical data routing and have applications to computers, communications networks, the Internet and other networks, time delays in RADAR, and numerous other applications.
• Natural and synthetic optical materials have a wide range of potential crystal lattice symmetries. (A well-known catalog of all crystal space groups is the
• each crystallographically-equivalent subset of lattice sites may contain ions or molecules with a finite number of different spatial orientations.
• the optical transitions of electrons in the ions or molecules can be described by two quantum energy levels and a transition dipole moment .
• transition dipole moments have a plurality of different spatial orientations, according to the different orientations of the crystallographically- equivalent sites noted above.
• Light beams on the other hand, must have single optical propagation directions and polarization states relative to the crystal, with the consequence that the light polarization will have a plurality of different spatial relationships with otherwise identical ions or molecules.
• the interaction of the optical field and the two-level quantum systems can be characterized by the optical Rabi frequency:
• the Rabi frequency is determined not only by the magnitudes of the transition dipole moment and of the optical field, but also by the projection of one onto the other (vector projection or scalar product) .
• the presence of multiple optical Rabi frequencies generally reduces the effectiveness of the optical- electronic device due to consequent complex transient material polarization behavior and the optical interference or beating of the associated optical signal amplitudes radiated by the material.
• Such interference can in turn limit the optical-electronic system bandwidth and hence the response time and data handling capability in the optical-electronic application.
• the interference may also reduce the optical diffraction efficiency, i.e., the signal selection or deflection efficiency in such devices as optical data routers for optical communications networks and wavelength-division multiplexing systems .
• optical material had to be chosen from a small subset of available materials, most or all of which do not have a single set of identically-aligned and oriented crystallographically- equivalent dipoles; that represents a sacrifice in potential bandwidth, diffraction efficiency, and performance .
• the following example shows the difficulty of the high-symmetry single-site-orientation approach.
• a beam of radiation e.g. a coherent light beam, (or multiple beams of radiation) is propagated through a material having a generalized crystal symmetry with specific light propagation direction and polarization state specified relative to the conventional axes of crystal symmetry of the material (linear or elliptical polarization) . Since the material has a generalized crystal symmetry, the material's transition dipoles will have several independent transition directions; that is, the material will have a crystal lattice structure with a plurality of unaligned, differently-orientated dipoles at crystallographically-equivalent sites .
• the invention involves a procedure for determining a suitable optical propagation direction and polarization state that projects equally on the respective directions of the transition dipoles, or more typically a subclass of the dipoles, and which is orthogonal to the respective directions of any remaining transition dipoles, i.e. all dipoles of the original subset not within the subclass of dipoles.
• the radiation beam is polarized, linearly or otherwise, relative to the axes of symmetry to equally project onto each of the dipoles within the subclass of dipoles.
• the propagating radiation beam is polarized identically with respect to each of the dipoles within the subclass and orthogonally to dipoles outside the subclass of transition dipoles, and accordingly, equally projects onto each of the dipoles within the subclass of transition dipoles.
• the propagation of the polarized radiation beam through the material actively excites ions in the subclass of dipoles so as to induce them to oscillate cooperatively.
• the dipoles of the ions outside the subclass preferably are not oscillated.
• each of the dipoles in the subclass are oscillated at the substantially same Rabi frequency and have a substantially equal transition intensity.
• the relationship of the propagation direction and polarization to the axes of crystal symmetry will change dependent upon the selection of dipoles forming the subclass of dipoles.
• the subclass of the dipoles is selected such that there exists a special direction, specified relative to the conventional axes of crystal symmetry, that projects equally on the respective transition dipoles within the subclass and is orthogonal to the respective transition dipoles of the remainder of the dipoles.
• a system for propagating a beam of radiation through a material having a plurality of unaligned, differently-orientated crystallographically-equivalent transition dipoles includes a monochromatic frequency-agile radiation emitter (or several emitters) for emitting a beam (or multiple beams) of radiation along a path towards the optical-electronic material.
• An optical controller or encoder for each beam made up, for example, of an acousto-optical, electro-optical, or other modulator or combination of modulators imposes amplitude or phase information on the beam of radiation (or prepares the beam to manipulate another of the several radiation beams) .
• a possibly-two-dimensional deflector makes adjustments in the beam direction as may be required by the optical-electronic device application.
• Input optics direct the radiation beam(s) to the crystalline material where the radiation-material interaction critical to device performance occurs.
• a polarizer is configured (or polarizers are configured) to polarize each emitted radiation beam in a direction such that the radiation beam polarization (s) has (have individually) substantially the same projection with respect to multiple dipoles making up a subclass of transition dipoles.
• the typically very small angles between multiple incident radiation beams can be freely varied while maintaining the desired single Rabi frequency behavior (the garnet example illustrates that) ; in other cases the small angles typically involved between several beams mean that the conditions can be met simultaneously to a good approximation.
• the optical -electronic material there are output optics and an array of radiation detectors or other independent receiving channels such as optical fibers for the signals .
• Figure 1 shows the relative orientations of the six orientationally-inequivalent but crystallographically- equivalent dodecahedral sites in the crystal lattice of Y 3 A1 5 0 12 .
• This is a particularly complicated system that has been chosen to illustrate the general procedure that is applicable to any crystalline material (there is a non-denumerable number of possible crystalline materials to which these concepts apply - limits are described below) .
• Figure 2 shows an example of an unoptimized coherent interaction (where beating reduces signal amplitude) and shows two different examples, wherein identical optical fields are used, of optimized coherent interaction for the material of Figure 1.
• Figure 3 depicts an optical -electronic device configured to transmit radiation through the generalized optical material in accordance with the optimized material interaction of the present invention.
• Figure 1 depicts an optical material 90 having a particularly complicated crystal symmetry.
• the material 90 is garnet, which serves to illustrate the application of this invention to the symmetry properties of a generalized material, as previously noted in the discussion of the Background Art.
• the chemical formula for garnet crystals is A 3 B 2 C 3 0 12 -
• the A ions occupy six crystallographically-equivalent but orientationally- inequivalent versions of this single type of crystallographic site with orientations labeled 10-60, each with dodecahedral point symmetry.
• the garnet material is doped with rare earth ions which typically substitute for the A ions and experience the same dodecahedral symmetry with respect to the six sites
• Each of the sites 10-60 has local orthogonal axes, x, y and z, but as the lozenge symbols in Fig 1 illustrate, these three directions are not equivalent. In Figure 1, the local axes are shown only for site 10.
• each of the sites 10-60 will have a different orientation since, unlike in materials with a single set of identically aligned and oriented crystallographically-equivalent sites, the material 90 has a complicated crystal symmetry and accordingly, differently-oriented, unaligned, but crystallo- graphically-equivalent sites; these six orientations are determined by the so-called O h or Ia3d symmetry (standard international crystallographic symbols) .
• the use of the material 90 in optical-electronic devices is not optimum due to the plurality of different orientations of these six sites arising from the garnet crystal symmetry or to another plurality in the generalized case. More particularly, radiation directed through the material 90 in the conventional manner will oscillate ions at the sites 10-60 at six different optical Rabi frequencies which will result in optical interference and transient material polarization behavior such that the effectiveness of the device will be substantially degraded as compared to a device with identically aligned and oriented sites. This optical interference is illustrated by the observed optical nutation shown in Figure 2 line C.
• the effectiveness of an optical-electronic device incorporating material 90 as the radiation interaction medium could be substantially improved and the associated transient material polarization behavior simplified.
• the system bandwidth and diffraction efficiency could be substantially enhanced.
• this can be accomplished by properly selecting the radiation propagation direction and the radiation polarization state specified relative to the conventional axes of crystal symmetry of the material 90.
• the transition dipoles at each of the sites 10-60 necessarily lie along either the local x, y, or z axes for different sites and electronic states of the material.
• the possible electronic states of the material involved in the optical transitions are labeled by conventional symmetry designations r 1# T 2 , T 2 , and r 4 .
• the symmetry transformation properties of the transition electric dipoles together with the symmetry properties of the two quantum states involved in the transition select either the p x , p y , or p z dipole corresponding to the local axes shown in Fig 1. Since the local x, y and z axes of each of the six crystallographically-equivalent sites 10-60 are oriented differently from each other site, six different orientations of dipoles corresponding to the six different sites 10-60 are likewise present.
• the electric or magnetic field vector will typically have unequal projections with respect to each of the six orientations of transition dipoles. This will necessarily result in unequal transition intensities for each of the sites 10-60 and consequently different Rabi or nutation frequencies .
• Conventional propagation of the radiation beam along the so-called crystallographic ⁇ 111> direction forces this multiple Rabi frequency situation to occur.
• the Rabi or nutation frequencies for at least a subclass of the totality of sites, 10-60 in the present illustration can be made equal; simultaneously, sites outside the chosen subclass are made inactive.
• a cooperative oscillation at a single Rabi frequency can be achieved in the material 90.
• the radiation field direction can be chosen so that all sites being excited by the radiation have the same projection of the radiation field onto the transition dipoles.
• the dipole vectors precessing at different rates under the driving influence of the radiation beam or field thereby causing unwanted cancellations of the material polarization (i.e., the sum of all dipole vectors)
• the dipole vectors will precess at substantially, if not exactly, the same rates when driven by the radiation beam or field and no cancellations of the material polarizations of the precessing dipole vectors will occur.
• the proper selection of the radiation field or beam configuration is established by first determining a direction that equally projects on a subclass of the dipoles (corresponding to a subclass of the sites 10-60 for the garnet material case) and which is perpendicular to the remaining dipoles (at the remaining sites 10-60 in the garnet case) .
• This direction has a specific relationship (or perhaps several specific relationships) to the axes of crystal symmetry of the material .
• the radiation beam is then propagated perpendicular to and polarized along this direction (in the linear polarization case) so as to equally project on the dipole moments .
• the radiation beam or field will be polarized at an equal angle with respect to each of the transition dipoles in the subclass of dipoles that are actively oscillated.
• the radiation beam or field may be linearly or otherwise polarized, so long as the radiation beam or field equally projects onto the dipoles within the chosen subclass of dipoles.
• the radiation field vector i.e., the radiation polarization, has the same projection relative to all transition dipoles in the subclass of dipoles and hence identical transition intensities.
• the induced transitions for the three sites 10, 40 and 60 will be at identical Rabi frequencies (if the dipole is along y) ; the other sites are not active.
• Figure 2 depicts the light emission intensities over time caused by propagating and polarizing the radiation beam or field as described above with respect to special directions specified relative to the crystal symmetry axes and corresponding in this case to axis B (line A in
• FIG. 2 or D (line B in Fig. 2) , as depicted in Figure 1.
• a third line on the graph depicts the transition intensity over time caused by a conventionally configured radiation beam or field with respect to the crystal lattice structure of material 90 of Figure 1.
• Figure 2 indicates the beneficial effects of the single Rabi frequency behavior resulting from the implementation of the inventive technique described herein.
• the dipoles of the sites 10-60 that are actively oscillated exhibit the desired cooperative properties under coherent illumination.
• the above described technique allows optical materials that may have otherwise beneficial properties to be utilized. It should be noted that the above reflects the results of testing carried out on 0.1%.
• the 3 H 6 (1) to 3 H 4 (1) transition i.e., 793.374 nm in a vacuum, is an electric dipole transition, and the transition dipole between these states is directed along the local y axis.
• Figure 3 depicts a simplified exemplary system configuration in accordance with the present invention.
• the depicted configuration will typically also include other elements such as collimators, lenses, etc., inserted along the radiation beam path as may be desirable for the particular implementation.
• the crystal lattice structure of the material 90 includes sites 10-60 as have been described above with reference to Figure 1.
• the system includes a radiation beam emitter 210 (or an array of such emitters) which is shown as a laser source but could be another radiation source as may be suitable for the intended application.
• the radiation beam 215 emitted from the emitter 210 is propagated in the desired direction by the controller 220 which could, for example, be an acousto-optical modulator (AOM) or other suitable control device for propagating the radiation beam 215 along the proper path with respect to the selected axis of crystal symmetry of the material 90 and modulating its intensity, frequency, and phase.
• the propagating beam 225 is output from the controller 220 to a polarizer 230 that polarizes the radiation beam with respect to the selected axis of crystal symmetry.
• the propagating polarized beam 235 is transmitted along the proper path through the material 90.
• the radiation beam is propagated and polarized based upon the axis B of Figure 1 being the special crystal symmetry direction.
• the beam 215 emitted by the laser 210 is directed by the controller 220 such that the radiation beam 225 output from controller 220 propagates along a path coinciding with axis A of Figure 1.
• the polarizer 230 polarizes the beam such that the output beam 235 is polarized linearly along the axis of crystal symmetry B.
• the polarizer 230 polarizes the emitted radiation beam at substantially the same angle with respect to each of the dipoles at the sites 10, 20, 30, and 40, and the controller 220 propagates the radiation beam perpendicular to the direction along which the beam is polarized by polarizer 230. Accordingly, identical Rabi frequencies are induced at sites 10, 20, 30, and 40 with the resultant constructive intensity as indicated in Figure 2, line A. This result is accomplished even though the material 90 is formed of unaligned, differently orientated crystallographically- equivalent transition dipoles at the sites 10-60. Hence optical interference is substantially reduced, if not eliminated, and transient material polarization behavior is significantly simplified.
• the invention provides a technique for increasing the speed and bandwidth characteristics of optical-electronic transmissions and interactions, reducing material polarization interference in optical-electronic transmissions and interactions, and optimizing optical transition probability in optical- electronic transmissions and interactions through a wide range of optical materials.
• a highly effective optical system configured to implement the technique is additionally described. It will also be recognized by those skilled in the art that, while the invention has been described above in terms of only one or more preferred embodiments, it is not limited thereto. The various features and aspects of the above described invention may be used individually or jointly. Further, although the invention may be described in the context of its implementation in a particular environment and for particular purposes, e.g.
• the single Rabi frequency direction can be found in Table 1 for all possible crystals. As can be seen from the table, all non-cubic crystals have at least one direction along which all dipoles project equally. For dipoles at sites of higher symmetry, additional directions are given with the same property. For crystals with cubic symmetry, dipoles at site symmetry higher than and including orthorhombic can always project equally onto some axes of the crystal . For sites with even lower symmetry, though, no general solution is given, but it is still possible to find a partial solution for many cases of interest. A partial solution means that a solution exists for some electronic states of the active ions or molecules but not for others . For example, in Eu:Y 2 0 3 , which is a potentially important material in the optical-electronic applications, the Eu 3+ ion substitutes for Y 3+ at a C 2 site in the cubic crystal
• Table 7 F 0 - S D 0 is an electric dipole pointing in the C 2 direction and there are several directions in the crystal that project to the dipoles equivalently.
• Table 1 A table listing all the single Rabi frequency directions for all crystal symmetries and every possible site symmetry for each crystal symmetry. When there are several possibilities for the same symmetry label, the labels C 2 ' an C 2 ' ' are also used in addition to C 2 , and ⁇ d , ⁇ v are used for the vertical mirror planes in the convention of Koster, Dimmock, Wheeler, and Statz, Properties of the Thirty-Two Point Groups, MIT Press, 1963.
• an important aspect of the invention resides in optimizing the coupling of the radiation to the dipoles of the optical material.
• This coupling eventually results in changes to the material (for example in optical data storage applications) and changes in the radiation beams (for example in signal processing applications or in readout of stored information) .
• this coupling is called the "coherent interaction of optical radiation beams or fields with ion doped or molecular crystals of various types".
• the direction of propagation is used to optimize that coupling.
• the dipoles represent, model, or describe the nature of a bulk material.
• the optimization of coupling is the key idea. "Propagation" becomes important as it affects this coupling.
• the principles of the invention are applicable in any optical-electronic application which is based on the coherent interaction of optical radiation beams or fields with ion-doped or molecular crystals.
• Devices which use the concepts include optical data storage, real-time optical signal processing, quantum computers, coherent computers, and optical data routing.

Landscapes

• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Holo Graphy (AREA)
• Optical Recording Or Reproduction (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=21987872

Family Applications (1)

Country Status (5)

Cited By (1)

Citations (6)

Family Cites Families (5)

• 1998
  • 1998-07-28 AU AU86693/98A patent/AU8669398A/en not_active Abandoned
  • 1998-07-28 WO PCT/US1998/015724 patent/WO1999005507A1/en not_active Application Discontinuation
  • 1998-07-28 JP JP2000504444A patent/JP2001511535A/ja not_active Withdrawn
  • 1998-07-28 CA CA002298557A patent/CA2298557A1/en not_active Abandoned
  • 1998-07-28 EP EP98938090A patent/EP1012569A4/en not_active Withdrawn

Patent Citations (6)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events