WO2006113783A1

WO2006113783A1 - Method for the production of high electric fields for pyrofusion

Info

Publication number: WO2006113783A1
Application number: PCT/US2006/014708
Authority: WO
Inventors: Seth J. Putterman; James K. Gimzewski; Brian B. Naranjo
Original assignee: University of California Berkeley; University of California San Diego UCSD
Current assignee: University of California Berkeley; University of California San Diego UCSD
Priority date: 2005-04-18
Filing date: 2006-04-18
Publication date: 2006-10-26
Anticipated expiration: 2007-10-18

Abstract

An apparatus for generating an electric field comprises a pyroelectric element having one or more layers of optically absorptive material disposed within the element. The optically absorptive layers are configured to selectively absorb light of a particular wavelength from a beam of light incident on the pyroelectric element to selectively heat a region of the pyroelectric element adjacent the optically absorptive layers and thereby form a thermal gradient across the pyroelectric element, wherein the thermal gradient generates an electric field external to the pyroelectric element. The optically absorptive layers may comprise nanoparticles of selected materials that are configured to absorb at selected wavelengths and/or intensities.

Description

METHOD FOR THE PRODUCTION OF HIGH ELECTRIC FIELDS

FOR PYROFUSION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisional application serial number 60/672,910, filed on April 18, 2005, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

OR DEVELOPMENT [0002] Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL

SUBMITTED ON A COMPACT DISC [0003] Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION [0004] A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0005] This invention pertains generally to pyroelectric crystals, and more particularly to a multilayer pyroelectric crystal. 2. Description of Related Art

[0006] Pyroelectric crystals (such as those made of LiNbOs) are widely used as detectors of infrared and THz radiation. More recently, it has been discovered that they could be used to produce energetic electron beams if heated or cooled in dilute gas atmospheres means that they can be used to produce x-ray fluorescence for elemental analysis of complex materials, such as tree leaves, rocks, air filters, blood samples, etc.

[0007] Therefore, more efficient pyroelectric crystals/systems that are able to generate large thermal gradients under low power and fast cycling times are of paramount interest.

BRIEF SUMMARY OF THE INVENTION

[0008] An aspect of the invention is an apparatus for generating an electric field. The apparatus comprises a pyroelectric element having one or more layers of optically absorptive material disposed within the element. The one or more optically absorptive layers are configured to selectively absorb light of a particular wavelength from a beam of light incident on the pyroelectric element to selectively heat a region of the pyroelectric element adjacent the optically absorptive layers and thereby form a thermal gradient across the pyroelectric element, wherein the thermal gradient generates an electric field external to the pyroelectric element.

[0009] The pyroelectric element preferably comprises a pyroelectric crystal, such as lithium tantalite or lithium niobate.

[0010] In one embodiment, the one or more optically absorptive layers comprise a first optically absorptive layer and a second optically absorptive layer separated from the first optically absorptive layer by a section of the pyroelectric material. The first optically absorptive layer is configured to absorb light at a first wavelength and second optically absorptive layer is configured to absorb light at a second wavelength different from the first wavelength. When a first incident light beam having the first wavelength and a second incident light beam having the second wavelength are directed at the first and second optically absorptive layers, the first and second light beams selectively heat the first and second optically absorptive layers at different rates.

[0011] In one mode of the current embodiment, a first laser is configured to direct the first incident light beam at the pyroelectric material, and a second laser is configured to direct the second incident light beam at the pyroelectric material. The first and second lasers are configured to direct the first and second incident light beams at different intensities or pulse lengths, so that the first optically absorptive layer heats up at a different rate than the second optically absorptive layer

[0012] Large numbers of such layers, of extremely small thicknesses, may be arranged to rapidly generate a uniform thermal gradient across the element.

[0013] In another embodiment, a first laser is configured to direct a broadband beam at an intermediary optic element configured to split the broadband beam into the first incident light beam and the second incident light beam, both directed at the pyroelectric material. In such an embodiment, the first optically absorptive layer is configured such that it absorbs light at a faster rate than the second optically absorptive layer so that the first optically absorptive layer heats at a faster rate than the second incident light layer.

[0014] In a preferred embodiment, the one or more optically absorptive layers may comprise nanoparticles disposed between adjacent layers of pyroelectric material, wherein the nanoparticles are configured such that each of the one or more optically absorptive layers absorbs light at a different wavelength. The nanoparticles may also be configured such that they absorb light at different rates, e.g. by altering the dimensions, structure, orientation, density etc. of the nanoparticles. The nanoparticles may comprise one or more of the following: nanotubes, nanoshells, quantum dots or quantum wells. The nanoparticles may also be configured to create Raman scattering of the incident light.

[0015] In another embodiment, the one or more optically absorptive layers are configured to absorb light at a frequency ranging from 10 nm to 1mm.

[0016] In addition, the apparatus may further include a heat sink coupled to the pyroelectric element, wherein the heat sink is configured to selectively cool the pyroelectric element. The heat sink may comprise a thermally responsive actuator, thermoelectric heat sink, Peltier cooler, or similar device that intermittently cools the pyroelectric material.

[0017] Another aspect of the invention is a method for generating an electric field. The method comprises directing a plurality of light beams each having different wavelengths incident on a pyroelectric element having a plurality of optically absorptive layers dispersed between adjacent sections of the pyroelectric material. Each of the plurality of optically absorptive layers is configured to absorb at different wavelength ranges to allow selectively heating the plurality of optically absorptive layers to form a thermal gradient across the pyroelectric element, and thereby generate an electric field as a result of the thermal gradient across the pyroelectric element.

[0018] The plurality of light beams may be emitted from a plurality of lasers operating at different intensities or pulse lengths, or from a single laser beam split into a plurality of light beams having different wavelengths;

[0019] In one embodiment of the current aspect, selectively heating the plurality of optically absorptive layers comprises: directing a first incident light beam having a first wavelength and a second incident light beam having a second wavelength at the pyroelectric element; absorbing the first incident light beam with a first optically absorptive layer configured to absorb light at a first frequency range including the first wavelength; absorbing the second incident light beam with a second optically absorptive layer configured to absorb light at a second frequency range including the second wavelength; and selectively heating the first and second optically absorptive layers at different rates.

[0020] Another aspect of the present invention is a method of generating neutrons. The method comprises locating a probe tip adjacent a pyroelectric element in an environment containing a gaseous source of neutrons, directing light at the pyroelectric element to generate a thermal gradient across the pyroelectric element, generating an electric field external to said pyroelectric element as a result of said thermal gradient, concentrating the electric field at the probe tip. and accelerating a deuteron beam at a target to produce a neutron flux. [0021] Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS

OF THE DRAWING(S) [0022] The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: [0023] FIG. 1 is a side view of a multi-layer pyroelectric crystal in accordance with the present invention.

[0024] FIG. 2 is perspective view of the crystal of FIG. 1.

[0025] FIG. 3 is a system of generating a thermal gradient in accordance with the present invention. [0026] FIG. 4. is a graph of an exemplary thermal gradient across the crystal of FIG. 1. [0027] FIG. 5 is an alternative system for generating an electric field in accordance with the present invention. [0028] FIG. 6 illustrates a heat sink with bimetallic actuator coupled to a pyrocrystal. [0029] FIG. 7 illustrates a heat sink with Peltier cooling coupled to a pyrocrystal. [0030] FIG. 8 illustrates a heat sink with Peltier cooling coupled to a pyrocrystal at various layers within the crystal. [0031] FIG. 9 illustrates a pyrofusion device using the pyrocrystal of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0032] Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in FIG. 1 through FIG. 9. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. [0033] FIG. 1 illustrates a pyroelectric crystal 10 in accordance with the present invention. Crystal 10 comprises a pyroelectric crystal, such as lithium tantalate (LiTaO₃), lithium niobate (LiNbO), or any other material that generates a voltage when it is heated or cooled. The crystal 10 comprises a laminated structure having a plurality of optically absorbing layers 20-28, that are dispersed within sections of pyroelectric crystal 12, e.g. lithium tantalite. Although FIGS. 1-9 illustrate a crystal that has five optically absorbing layers 20-28, it is appreciated that any number of layers, from 1 , to thousands or more may be used.

[0034] As shown in FIG. 2, the crystal 10 may have a cylindrical shape.

However, rectangular, cubic, or other types of shapes or dimensions may be used as practicable.

[0035] Each of the optically absorbing layers 20-28 comprise a material, composition, and or structure that is configured to absorb light at a particular wavelength, and heat up in response to the to an incident beam of light. As one part of the crystal 10 heats up, while the other stays cool, a thermal gradient is generated, which, in turn, generates an electrostatic field.

[0036] Referring to FIG. 3, each of the layers 20-28 may be configured to absorb light at a particular frequency or frequency range, e.g. layer 20 absorbs at λi, layer 22 absorbs at λ₂, layer 24 absorbs at Kz, layer 26 absorbs at λ₄, layer 28 absorbs at λ₅, etc. for how many absorption layers are present. Accordingly, a series of light sources 40-46 (such as a laser, LED, flash lamp, other light source) are directed at front surface 14 of the crystal 10, and propagate through the crystal. Each laser emits an incident light beam at a particular wavelength corresponding to the absorption wavelength of one of the layers 20-28. For example, laser 40 emits beam 30 having wavelength λi. Since λi is the wavelength that layer 20 absorbs at, it will correspondingly heat that section of crystal from the resonance occurring at that wavelength. Accordingly, laser 42 emits beam 32 having wavelength λ₂. The materials are selected so that layer 20 does not absorb at K₂ (or absorbs very little), and layer 22 does not absorb at λ₂. Thus, beam 32 will pass through layer 20 with relatively little interruption or absorption, thereby striking layer 22, which absorbs at, and correspondingly heats that section of crystal from the resonance occurring at that wavelength. Accordingly, laser 44 emits beam 34 at λ_3l laser 46 emits beam 36 at λ₄, and laser 48 emits beam 34 at λs, to heat each layer variably.

[0037] As shown in FIG. 4, the lasers 40-48 may be each adjusted in power or output, or temporal shot time, to selectively heat each layer differently. The result is a thermal gradient (ΔT) from T1 at the front face 14 of the crystal, to T2 at the rear edge 16 of the crystal. Although merely one layer of absorptive material may be positioned at one end of the crystal, this may resulting in a sharp ramp or exponential increase in temperature over the crystal. For many applications, a more linear or uniform increase in temperature may be desired, as shown in the graph of FIG. 4.

[0038] Although FIG. 4 shows temperature increasing from front face 14 to rear race 16, the layers 20-28 may be configured with materials such that face 14 is hot and rear race 16 is cool. This may be particularly useful where heat sinks or other devices are desired on the cold side. In addition, this may be beneficial where some of the absorptive layers still absorb at other frequencies, such that successive light does not work against the directional gradient.

[0039] The system shown in FIG. 3 may produce large thermal gradients in short periods of time, e.g. ΔT of several hundred degrees Celsius in milliseconds or less. This may result in generation of an electric field greater than 100keV.

[0040] The absorptive layers 20-28 may comprise a number of known materials or structures known in the art to absorb light at certain frequencies. However one preferred composition is that of nanostructures. Nanostructures, such as nanoparticles, nanotubes, nanoshells, quantum dots or wells, etc., allow very tunable, precise and thin layers to be produced, thereby allowing large numbers of layers in a small area.

[0041] The absorptive layers 20-28 may also be configured to induce surface enhanced Raman scattering (SERS). Raman scattering is an inelastic scatting of light in which the incident the light either imparts rotational or vibrational energy to the scattering molecules of the material it is incident on. The geometry and dimensions of the nanoparticles may be deposited on each of layers 20-28 to systematically control the plasmon frequency of the nanostructure. For example, triangles, nanorings, nanoshells, etc. may be created in various sizes or orientations to correspond to a resonance at a particular frequency or wavelength (see J. B. Jackson and N. J. Halas, "Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates," Proc. Natl. Acad. Sci. USA 101 , 17930- 17935 (2004); C. Loo, A. Lowery, N. Halas, J. West, and R. Drezek, "Immunotargeted Nanoshells for Integrated Cancer Imaging and Therapy," Nano Letters ASAP (2005), both incorporated by reference in their entirety).

[0042] Various materials may also be used that are known to have certain absorptive properties at various wavelengths. For example, nanoparticles may be used having compositions of AG, AU, InAs, CdSe, GaAs, CdTe, CdZnSe, Si, or similar compounds or materials may be used. The nanoparticle layers may be configured to absorbed at a broad spectrum of wavelengths, e.g. ranging from UV, to visible light, to IR.

[0043] Various techniques may be used to fabricate the nanoparticles, such as sputtering, etching, growing, etc. Specific techniques in engineering nanoscale structures may be used, such as that described in 6,673,330, filed on January 16, 2004, and X. Liu, K. Terabe, M. Nakamura, S.Takekawa, and K. Kitamura. "Nanoscale chemical etching of near-stoichiometric lithium tantalate," Journal of Applied Physics 97 (2005), K. Terabe, M. Nakamura, S. Takekawa, S. Higuchi, Y. Gotoh and Y. Cho. "Microscale to nanoscale ferroelectric domain a near-stoichiometric LiNbO₃ crystal," Applied Physics Letters 82(2) (2002), K. Terabe, X. Liu, X. Li and K. Kitamura. '"Ferroelectric Domain Architecture for Novel Devices," Transactions of the Materials Research Society of Japan, March (2005), K. Terabe, M. Nakamura, S. Takekawa, K. Kitamura, S. Higuchi, and T. Togashi "Domain and surface engineering of ferroelectric crystal LiNbO₃ for novel devices," Materials Technology 19(3) (2004), all incorporated herein by reference in their entirety. [0044] Referring now to FIG. 5, an alternative system may be employed for selectively heating various parts of a crystal. Crystal 70 may be configured with optically absorptive layers 80-88 disposed between pyroelectric crystal sections 12. In this configuration, one light source 72 or laser is used. This configuration may be particularly useful where quite a large number of layers are used, and having a corresponding number of lasers would be cost or size prohibitive. In this embodiment, a broadband beam 76 from laser 72 is directed at optical element 74 that splits the beam 76 into a number light beams 90-98 each having different wavelengths. Optical element 74 may comprise any number of devices, such as a grating, prism, etc., that are known in the art to perform this function. Each of the beams 90-98 are then directed at the crystal 70 such that each is selectively absorbed by different layers 80-88 to form the desired thermal gradient. Because the light source 72 is emitting at the same intensity, each of the layers may be selectively configured to generate heat at varying rates. For example, the size, orientation, and density of nanoparticles in each of the layers may be varied such that layer 80 heats up faster than layer 88, and so on.

[0045] In another embodiment, 74 may also comprise a plurality of filters that allows a certain area or portion of light at each wavelength to pass through to the crystal, thereby selectively dictating how much light of each wavelength strikes each layer. This can be used in combination, or instead of, the differing density of nanoparticles approach to vary how fast each layer 80-88 heats.

[0046] Referring now to FIGS. 6-8, various forms of cooling devices may be employed to cool the device. Because heat will eventually dissipate (e.g. via conduction) throughout the crystal, the longer the incident beams are continuously directed on the crystal, the weaker the gradient will become. Thus, it is beneficial to pulse the laser(s) to cycle the crystal 10, thereby maintaining the desired thermal gradient. However, the pulses need to be spaced apart some length of time, or the heat will continue to conduct to the "cool" side of the crystal.

[0047] Heat sinks, heat pumps, or other heat directing devices may be positioned on the crystal (e.g. the "cool" side of the crystal) to decrease the cycling time for each successive pulse. For example, a heat sink 56 may be positioned at one end 16 of the crystal, as shown in FIG. 6. In this configuration, the absorptive layers 20-28 are reversed from FIG. 1 , so that the back side 16 is cooler than front side 14. However, continuous contact with the heat sink may be counterproductive to the heating of the crystal in general. Therefore, an actuator 50 may be positioned on back side 16 so that the crystal 10 is cooled intermittently.

[0048] Actuator 50 may comprise a bimetallic thermally responsive actuator that has two layers 52, 54, each having different thermal coefficients that draw the actuator toward the heat sink to contact the neat sink when the temperature reaches a certain range.

[0049] As shown in FIG. 7, thermoelectric cooling may also be employed. For example a Peltier cooler 58 may be employed on one end 16 of the crystal 10. With Peltier cooling, current (which may be intermittent) is passed through (via power supply 68) two dissimilar metals or semiconductors (e.g. n-type 60 and p-type 62) that are connected in series to the crystal 10. The current drives the heat from one side to the other, cooling off the crystal.

[0050] Referring to FIG. 8, a Peltier cooler 58 may be applied to various arrays layers of crystal 10. For example, contacts 64, 66 may be variously positioned at locations around the circumference of the crystal. Alternatively, contacts may be layers (optically transparent but thermally conductive) disposed within the crystal.

[0051] In other embodiments, means of cooling may comprise spraying low- vapor non-wetting liquid (e.g. Hg or In) on one end of the crystal, laser cooling, cryogenic-cooling or a combination of any of the above methods.

[0052] By using the above systems, cycling times of less than ~1 kHz can be achieved, thus producing 10⁹ neutrons per second (when using in a fusion chamber as shown in FIG. 9, described in further detail below). By scaling arrays of approximately 10⁶ crystal sandwiches, roughly 10^1δ neutrons per second may be generated from a vacuum device the size of a football. With current fabrication processed, a crystal with up to millions arrays in a cube. The smaller dimensions promote faster cycling times to obtain large temperature gradients on a ms time scale

[0053] The above methods and apparatus illustrated in FIGS. 1-8 may be used for a number of applications. For example, by heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (>100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. The applicable reaction is D + D → ³He (820 keV) + n (2.45 MeV).

[0054] Because the spontaneous polarization is a function of temperature, heating or cooling a pyroelectric crystal in vacuum causes bound charge to accumulate on faces normal to the polarization. A modest change in temperature can lead to a surprisingly large electrostatic field. For example, heating a lithium tantalate crystal from 240 K to 265 K decreases its spontaneous polarization by 0.0037 Cm^"2. In the absence of spurious discharges, introducing this magnitude of surface charge density into the particular geometry of the setup shown in pending PCT Application No. 06/00113, filed January 03, 2006, and U.S. Provisional Application Nos. 60/641 ,302, filed January 03, 2005, both herein incorporated by reference in their entirety, gives a potential of 100 kV. Attempts to harness this potential have focused on electron acceleration and the accompanying bremsstrahlung radiation, but using the crystal to produce and accelerate ions has been studied much less. Seeking to drive the D-D fusion reaction, the current invention sets out a method of reliably producing an ion beam of sufficient energy (>80 keV) and current (>1 nA).

[0055] The crystal 10 of the present invention, along with a tungsten tip, may generate the high field (>25 V nm^"1) necessary for gas phase field ionization of deuterium. FIG. 9 illustrates a pyrofusion device 100 in accordance with the present invention. A cylindrical z-cut LiTaO₃ crystal 10 (with accompanying nanolayers) is mounted inside a chamber 102 containing deuterium gas, with negative axis facing outward. Light source 120 (which may comprise one or more lasers and intermediary optics) is located adjacent the crystal 10. On the opposite side of the crystal face, a copper disc (not shown) is attached, allowing charge to flow to a tungsten probe or needle 106 (e.g. shank diameter, 80μm; tip radius, 100 nm; length, 2.3mm). The probe geometry may be chosen accordingly (e.g. that the tip field was approximately 25 V nm^"1 when the crystal face was charged to 80 kV). D₂ pressure inside the chamber may be set using a leak valve and monitored with a D₂ compensated Pirani gauge. The target 104 (e.g. a molybdenum disc coated with ErD₂) is positioned across the chamber 102 from the crystal 10.

[0056] Upon heating of the crystal 10 by light source 120, crystal 10 polarizes charge, segregating a significant amount of electric charge near a surface, leading to a very large electric field. FIG. 9 also shows electric field equipotentials 108 and D⁺ trajectories 110. D2 molecules become ionized at the tip of probe 106, and the D+ ions 108 are accelerated toward the ErD2 target 104, where D + D fusion occurs, producing helium-3 and a 2.45-MeV neutron, a signature of D + D fusion.

[0057] A double tip system (not shown) may be employed where one crystal with alternate opposite +- polarities with another, so that loss of only 50% of the duty cycle is achieved.

[0058] To further increase efficiency of the system, millions of 3d arrays of the laminated crystals in a cube sphere of truncated icosahedrons may be implemented (not shown). The cube may be a vacuum enclosure using the same technology as a plasma flat panel TV or old tube in a radio. Such a configuration could deliver 10e15 neutrons per second.

[0059] This flux may provide the first steps to a new energy source or supplementary form of neutrons for devices involving plasmas of cyclotron related beams..

[0060] The above system can have application as a simple palm-sized neutron generator. We note that small (about centimeter-sized) pyroelectric crystals can produce ion beams of sufficient energy and current to drive nuclear fusion. We anticipate increasing the field ionization current by using a larger tip, or a tip array, and by operating at cryogenic temperatures. With these enhancements, and in addition using a tritiated target, we believe that the reported signal could be scaled beyond 10⁶ neutrons s^"1.

[0061] The device offers many potential applications. Because it emits X-rays, it could be used to aim the rays directly at a tumor to destroy it. It could also enable a handheld neutron scanner to identify explosives. For example, the pyroelectric crystal may be used for gamma-ray analysis at airports etc, using the neutron sources and means to achieve the higher fluxes, creation of X- rays from ions as well as electrons, point sources of x-rays, ions and neutrons

[0062] Other uses include: use for medical imaging and therapy, use for auxiliary neutrons in tokomaks and other controlled and uncontrolled thermonuclear devices, neutron bombs where in one giant burst a massive array of sources are triggered resulting in the destruction of the device, micro thrusters in miniature spacecraft and other applications related to Aerospace, use of neutrons as means of disabling electronic devices, use of sources in deployable remote devices such as robots and remote controlled airborne systems, use for mining and oil exploration by insertion into shafts and tunnels providing direct on line analysis of mineral deposits, contaminant pollution, and use as a compact focused ion generator for the front end of a neutron camera in associated particle imaging (API).

[0063] Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U. S. C. 112, sixth paragraph, unless the element is expressly recited using the phrase "means for."

Claims

CLAIMS What is claimed is:

1. An apparatus for generating an electric field, comprising: a pyroelectric element having one or more layers of optically absorptive material disposed within the element; wherein the one or more optically absorptive layers are configured to selectively absorb light of a particular wavelength from a beam of light incident on the pyroelectric element; wherein each of one or more optically absorptive layers are configured to selectively heat a region of the pyroelectric element adjacent the optically absorptive layers to form a thermal gradient across the pyroelectric element; and wherein said thermal gradient is configured to generate an electric field external to the pyroelectric element.

2. An apparatus as recited in claim 1 , wherein the pyroelectric element comprises a pyroelectric crystal.

3. An apparatus as recited in claim 2, wherein the pyroelectric crystal comprises lithium tantalate.

4. An apparatus as recited in claim 1 : wherein the one or more optically absorptive layers comprise a first optically absorptive layer and a second optically absorptive layer separated from the first optically absorptive layer by a section of the pyroelectric material; wherein the first optically absorptive layer is configured to absorb light at a first wavelength and second optically absorptive layer is configured to absorb light at a second wavelength different from the first wavelength; and wherein a first incident light beam having the first wavelength and a second incident light beam having the second wavelength are directed at the first and second optically absorptive layers, such that the first and second light beams selectively heat the first and second optically absorptive layers at different rates.

5. An apparatus as recited in claim 4, further comprising: a first laser configured to direct the first incident light beam at the pyroelectric element; and a second laser configured to direct the second incident light beam at the pyroelectric element; wherein the first and second lasers are configured to direct the first and second incident light beams at different intensities; and wherein the first optically absorptive layer heats up at a different rate than the second optically absorptive layer.

6. An apparatus as recited in claim 4, further comprising: a first laser configured to direct the first incident light beam at the pyroelectric element; and a second laser configured to direct the second incident light beam at the pyroelectric element; wherein the first and second lasers are configured to direct the first and second incident light beams at different pulse lengths; and wherein the first optically absorptive layer is configured to heat up at a different rate than second optically absorptive layer.

7. An apparatus as recited in claim 4, further comprising: a first laser configured to direct a broadband beam at an intermediary optic element; wherein the intermediary optic element is configured to split the broadband beam into the first incident light beam and the second incident light beam, both directed at the pyroelectric element; and wherein the first optically absorptive layer is configured such that it absorbs light at a faster rate than the second optically absorptive layer so that the first optically absorptive layer heats at a faster rate than the second incident light layer.

8. An apparatus as recited in claim 1 : wherein the one or more optically absorptive layers comprise nanoparticles disposed between adjacent layers of pyroelectric material; and wherein the nanoparticles are configured such that each of the one or more optically absorptive layers absorbs light at a different wavelength.

9. An apparatus as recited in claim 8, wherein the nanoparticles comprise one or more of the following: nanotubes, nanoshells, quantum dots or quantum wells.

10. An apparatus as recited in claim 8, wherein the nanoparticles are configured to create Raman scattering of the incident light.

11. An apparatus as recited in claim 1 : wherein the one or more optically absorptive layers are configured to absorb light at a frequency ranging from 10 nm to 1mm.

12. An apparatus as recited in claim 1 , further comprising: a heat sink coupled to the pyroelectric element; wherein the heat sink is configured to selectively cool the pyroelectric element.

13. An apparatus as recited in claim 12, wherein the heat sink comprises a thermally responsive actuator that intermittently cools the pyroelectric element.

14. An apparatus as recited in claim 12, wherein the heat sink comprises a thermoelectric heat sink to intermittently cool the pyroelectric element.

15. A method for generating an electric field, comprising: directing a plurality of light beams each having different wavelengths incident on a pyroelectric element; the pyroelectric element having a plurality of optically absorptive layers dispersed between adjacent sections of the pyroelectric material; wherein each of the plurality of optically absorptive layers is configured to absorb at different wavelength ranges; selectively heating the plurality of optically absorptive layers to form a thermal gradient across the pyroelectric element; and generating an electric field as a result of the thermal gradient across the pyroelectric element.

16. A method as recited in claim 15, wherein the plurality of light beams are emitted from a plurality of lasers operating at different intensities.

17. A method as recited in claim 15, wherein the plurality of light beams are emitted from a plurality of lasers operating at different pulse lengths.

18 A method as recited in claim 15, wherein the plurality of light beams are emitted from a single laser; wherein said beam from the single laser is split into a plurality of light beams having different wavelengths; and wherein the optically absorptive layers are configured to absorb light at different rates to selectively heat regions of the pyroelectric element.

19. A method as recited in claim 15, wherein selectively heating the plurality of optically absorptive layers comprises: directing a first incident light beam having a first wavelength and a second incident light beam having a second wavelength at the pyroelectric element; absorbing the first incident light beam with a first optically absorptive layer configured to absorb light at a first frequency range including the first wavelength; absorbing the second incident light beam with a second optically absorptive layer configured to absorb light at a second frequency range including the second wavelength; and selectively heating the first and second optically absorptive layers at different rates.

20. A method as recited in claim 19: wherein the first incident light beam and second incident light beam are individually directed via first and second lasers; and wherein the first and second lasers are controlled to direct the first and second incident light beams at different intensities to selectively heat the first optically absorptive layer at a different rate than the second optically absorptive layer.

21. A method as recited in claim 19: wherein the first incident light beam and second incident light beam are individually directed via first and second lasers; and wherein the first and second lasers are controlled to direct the first and second incident light beams at different pulse lengths to selectively heat the first optically absorptive layer at a different rate than the second optically absorptive layer.

22. A method as recited in claim 15, further comprising: selectively cooling the pyroelectric element.

23. A method as recited in claim 15, further comprising: intermittently cooling the pyroelectric element.

24. A method of generating neutrons, comprising: locating a probe tip adjacent a pyroelectric element in an environment containing a gaseous source of neutrons; directing light at the pyroelectric element to generate a thermal gradient across the pyroelectric element; generating an electric field external to said pyroelectric element as a result of said thermal gradient; concentrating the electric field at the probe tip; and accelerating a deuteron beam at a target to produce a neutron flux.

25. A method as recited in claim 24, wherein directing light at the pyroelectric element comprises directing a plurality of light beams each having different wavelengths at the pyroelectric element; the pyroelectric element having a plurality of optically absorptive layers dispersed between adjacent sections of the pyroelectric material; wherein each of the plurality of optically absorptive layers is configured to absorb at different wavelength ranges; and selectively heating the plurality of optically absorptive layers to form the thermal gradient across the pyroelectric element.

26. A method as recited in claim 25, wherein selectively heating the plurality of optically absorptive layers comprises: directing a first incident light beam having a first wavelength and a second incident light beam having a second wavelength at the pyroelectric element; absorbing the first incident light beam with a first optically absorptive layer configured to absorb light at a first frequency range including the first wavelength; absorbing the second incident light beam with a second optically absorptive layer configured to absorb light at a second frequency range including the second wavelength; and selectively heating the first and second optically absorptive layers at different rates.