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Nanoparticles trapped on resonant near-field structures engraved on a metallic substrate experience forces due to the engravings, as well as the image-like interaction with the substrate. In the case of normally incident optical excitation, the force due to the substrate is solely perpendicular to its surface. Numerical simulations are presented to demonstrate that under the combined influence of the aforementioned forces, a plasmonic nanoparticle can be repelled from the engraving along the substrate, while attracting it towards the substrate along its normal. This behavior can be achieved over a range of excitation wavelengths of the short wavelength mode of the coupled particle-substrate-trap system. To the best of our knowledge, this is the first illustration of an in-plane near-field optical barrier on a chip. The barrier is stable against resistive heating of the nanoparticle, as well as the induced non-isothermal flow. The wavelength-dependent switch between the proposed in-plane potential barrier and the stable potential well can pave the way for the gated transport of single nanoparticles, while holding them bound to the chip.

We describe a novel method for the recall of linear combinations of stored data pages in a volume holographic memory based on phase-code multiplexing. Recall is demonstrated by use of a compound phase-and-amplitude spatial light modulator in the reference beam path.

We examine the consequences of permanent phase distortions on the replay of transmission volume holograms with a phase-conjugated reference wave. In the absence of Bragg degeneracies and significant Bragg mismatch, for negligible dispersion in the spatial frequency response and for negligible variation in obliquity, phase-conjugated reference waves compensate for the effects of phase distortions and permit cross-talk-free multiplexing by using orthogonal reference waves. Spatial frequency dispersion, however, is a source of image distortion and cross talk.

We present a defect-enhancement system capable of detecting submicrometer defects on opaque periodic structures using real-time holography in photorefractive crystals. We detect 0.5-microm defects with ~90% success rate and 0.3-microm defects with85% success rate while inspecting an area greater than 1 mm(2) in real time. To our knowledge, these defects have an area 100 times smaller than those previously detected with any real-time holographic technique.

Optical interconnects for highly parallel computer architecture require high density optical switch arrays with dimensions of 100 × 100 or larger. Previously reported integrated switch array designs have been limited to 8 × 8 waveguides.1 While achieving high switching speeds and relatively low insertion losses, these switches are limited by long interaction lengths which lead to array dimensions of as long as 60 mm. Our switch design consists of two sets of parallel waveguides which intersect at right angles. The intersections are doped with a material to locally sensitize the region to the photorefractive effect. We have fabricated arrays based on standard Ti:LiNbO3 technology, using iron as a photorefractive sensitizer. Interfering beams are used to write an index grating at the waveguide intersections. This grating can then be used to diffract a portion of a data beam into the crossing waveguide. The diffraction efficiency depends on the length of the interaction region. Thus, insertion loss is traded off against switch density. We have constructed arrays of 15 × 15 up to 50 × 50 waveguides in an active area of only 5 mm square.

We describe what are to our knowledge the first photorefractive holographic recordings in a fiber. A plane-wave reference and an image-carrying object beam are incident upon the fiber in a reflection geometry. We report results on the angular sensitivity of the recordings, the image quality, and readout efficiency as a function of the reference-wave input angle when the object wave propagates along the bore of the fiber. These experiments are carried out for two relatively short, 4- and 8-mm, multimode 1-mm-diameter fibers. The results suggest that an array of fibers might favorably replace bulk materials for certain computer and signal-processing applications.

A photorefractive crystal (Bi(12)GeO(20)) is used to record double-exposure speckle patterns produced by Q-switched laser pulses in real-time speckle metrology and velocimetry applications. The speckle pattern displacements are immediately measured with an optical processor of the type used for measuring speckle displacements recorded on photographic film. Operation of the optical processor is described and compared with the case of film recording. Observed spatial and temporal recording properties of the crystal in this imaging configuration are discussed and compared with published results for single-frequency grating recording in photorefractives. The system is applied to measuring velocities of a moving solid object.

We report on the use of a sodium-seeded flame as an amplifying phase conjugator. The environment is unique in that a number density of 10(16) cm(-3) is maintained despite a lateral dimension of 1 mm. We combine two of these optically pumped flames to form a phase-conjugate resonator. Finally, we observe oscillation that is due to the action of a single flame and two pump beams.

Optical tomography offers advantages over conventional techniques for visualizing complicated mixing fluid flows. We have developed a system for acquiring 3-D measurements of concentration nonintrusively in a turbulent mixing coflowing jet. Holographic interferograms simultaneously record views from 36 different angles of the jet in 300 μs. The interferograms are processed tomographically to yield the index of refraction at all points in the jet. We show measurements of a 6-m/s helium jet mixing with air. The temporal resolution, spatial resolution, and SNR are very good.

The first observation to our knowledge of degenerate four-wave mixing in a sodium-seeded flame is reported. In addition, the theoretical dependence of the phase-conjugate output on the sodium concentration is verified experimentally, demonstrating the potential of this procedure for use as a diagnostic tool to measure species concentration in combusting or noncombusting media.

We report a high-intensity nano-aperture vertical-cavity surface-emitting laser (VCSEL) utilizing a bowtie-shaped aperture. A maximum power of 188 microW is achieved from a 180 nm bowtie aperture at a wavelength of 970 nm. The near-field full width at half-maximum intensity spot size 20 nm away from the bowtie aperture is 64 nm x 66 nm from simulation, and the peak near-field intensity is estimated to be as high as 47 mW/microm(2). This intensity is high enough to realize near-field optical recording, and the small spot size corresponds to storage densities up to 150 Gbits/in(2). The bowtie-aperture VCSEL also enables other applications, such as compact high-intensity probes for ultrahigh-resolution near-field imaging and single molecule fluorescence and spectroscopy.

We present a design for a subwavelength C-shaped optical waveguide with a 90 degrees junction that efficiently transports light while maintaining tight confinement with an exit spot size of lambda/7. Finite-difference time-domain simulations of perfect electric conductors and Au C-aperture waveguides are performed for optical frequencies. A design resonant near 780 nm is presented, with a spot size of 107 nm x 107 nm and an energy density enhancement factor of 10 for a bent waveguide of total length 1.4 microm.

We present a design of a linear optical waveguide that utilizes a C-shaped metallic nano-aperture that efficiently transports light while maintaining a spot size of lambda/10. The performance of a C-aperture waveguide is superior to both a regular ridge waveguide and other surface plasmon based metal nano-optical waveguides. The energy transport mechanisms are explained by the coupling of an aperture surface resonance and the thickness resonances inside the guide channel. Finite-difference time-domain simulations of gold C-aperture waveguides are performed for a 1.5 microm wavelength incident plane wave. The 1/e decay length in power transmission is predicted to be approximately 2.5 microm. The total power throughput is 1.66 for the 2.55 microm long guide, with an intensity 6 times that of the incident wave at a distance 120 nm from the exit plane, having a spot size of 150 nm.

Tilt tolerance of media is compared for bit-based and page-based holographic storage systems having an equal diffraction efficiency per bit detector, dynamic range of the medium, and surface recording density. We have formalized the diffraction efficiency degradation caused by aberrations of a reconstructing reference beam induced by tilt of the medium, using a coupled wave theory in the Fourier domain. The bit-based holographic storage system has a larger media tilt tolerance compared with a page-based system with relatively large page size.

Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides approximately 3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of approximately 0.1 lambda. Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture--or one of the related shapes--is linked to both a propagation mode in the aperture and local surface plasmons.

Recording of holographic gratings by 532-nm laser pulses in photochromic bulk aluminosilicate glass containing silver particles is demonstrated. A diffraction efficiency of 1.5% is achieved for readout at the same wavelength. The speed of grating formation as a function of pulse energy suggests that two-photon excitation is responsible for the recording. The light causes bleaching of an absorption peak near 417 nm, which corresponds to the excitation of surface plasmons on the silver, and broad darkening throughout the visible to the near infrared. A likely mechanism for the photochromic effect is discussed.

We report what we believe to be the first observation of photorefractive gratings in lead barium niobate (Pb(1-x)Ba (x)Nb(2)O( 6) ; PBN). A diffraction efficiency of 9% and a beam-coupling coefficient of 9 cm(-1) are obtained. After thermal fixing a grating of 0.5% is revealed at room temperature. We can improve this diffraction efficiency by optimizing fixing temperature, timing, and material parameters.

We report an improved fabrication method for C-shaped near-field apertures resonant in the near-IR regime. The apertures are created in a metal layer on a silicon nitride membrane using a focused ion beam and a through membrane milling technique that avoids two problems with fabricating very small apertures: gallium contamination and edge rounding. Finite-difference time-domain simulations predict a 63x more intense near field with a 2.2x smaller spot versus conventionally milled apertures. We verify the position of the simulated resonance peaks with experimental far-field transmission measurements where we also find an increase of 8.8x in intensity. Our method has applications to many other plasmonic devices including bow-tie and fractal apertures, periodic arrays, and gratings.

We present a C-shaped nanoaperture-enhanced Ge photodetector that shows 2-5 times the photocurrent enhancement over that from a square aperture of the same area at 1310 nm wavelength. We demonstrate the polarization dependence of the C-aperture photodetector over a wide wavelength range. Our experimental observation agrees well with finite-difference time-domain simulation results.

We describe laser ablation of Si under water by 5 ns, 355 nm and 100 fs, 800 nm pulses. Compared to that in air, an approximately twofold improvement in the ablation rate is found in water for femtosecond and nanosecond pulses. For higher laser irradiances, the plasma that forms at the water-air interface hampers further improvement of the ablation rate. We investigated the enhanced ablation process in water and found that the cavity-confinement geometry that increases the laser energy coupling to the target and allows more energy to be transferred to the cavity sidewalls plays an important role in the escalated material removal process. In addition, we show that the water layer that effectively reduces the oxidation and redeposition of the ablated debris is also responsible for improvements in the ablation process.

Tetragonal lead barium niobate (Pb(1-x)Ba(x)Nb(2)O(6);1-x

We demonstrate a novel apodization technique for holographic data storage using two-photon recording in stoichiometric lithium niobate. The gating light-intensity profile is used to achieve grating apodization inside the bulk of the crystal during recording in the transmission geometry. Experimental Bragg-selectivity curves and theoretical fits indicate a >20-dB drop in multiplexing cross talk.

We demonstrate a one-color one-beam pumping method for a three-dimensional two-step excitation fluorescent display with Er(3+) -doped ZBLAN glass. A localized green fluorescent spot is obtained by use of a focused pump-light beam at 979 nm. The quantum efficiency of the two-step excitation fluorescence is investigated in a time-dependent analysis and an experiment with a pulsed pump light.

Polymer films doped with 2-(5, 5-dimethyl-3-styryl-cyclohex-2-enylidene)-malononitrile chromophore and various sensitizers have been prepared and characterized. The material exhibits high sensitivity in the red region (S=0.26 cm(2)/J at lambda=633 nm), a large dynamic range (Dn=-0.05) , and large transient two-beam coupling gain (G=110 cm(-1)) . Self-diffraction effects, such as energy and phase coupling, and photoinduced scattering are studied.

We present a novel digital holographic data storage system based on wavelength multiplexing in 90 degrees geometry, using an automated tunable diode laser and a lithium niobate crystal. The automatic storage and retrieval of a 60-kbyte data file, as well as the limitations and future implementations of the system, are discussed.

We describe a digital holographic data storage system that uses in situ thermal fixing to achieve nonvolatile readout. The system was used to store and fix 530 holograms representing 1.7 MB of digital data. The system demonstrates that fixing by heating after recording gives adequate performance for multiplex holography in the perpendicular recording geometry. The postrecording heating procedure is preferred over high-temperature recording in the perpendicular geometry to achieve Bragg matching for the entire signal angular bandwidth.

We introduce the concept of traveling grating envelopes to study the erasure dynamics in bulk photorefractive media. This new technique provides considerable physical insight into the observed photorefractive transients. We propose and demonstrate experimentally, in a Ce-doped SBN:60 crystal, two novel ways of extending the grating lifetime by trapping the grating envelope inside the medium. The incident beam ratio and the readout geometry have the largest effect on how long the grating can be read out.

We explore theoretically and experimentally how application of an electric field to a photorefractive crystal affects the recording and the readout of holograms. We consider, for the first time to our knowledge, the effects of fringe bending caused by nonlinear two-wave mixing on the change in Bragg condition and diffraction efficiency as a function of the applied electric field. Practical performance limitations for holographic data storage and image amplification are discussed.

Growth-induced striations in photorefractive media scatter transmitted light, degrading their performance in holographic applications. We model this phenomenon by considering the striations to be a permanent hologram within a medium and compare it with experimental results in a striated strontium barium niobate crystal. We show that the construction of the phase-conjugate signal beam by a phase conjugate of the transmitted reference beam alleviates the effects of distortions that are due to striations.

Photorefractive gratings stored in single-crystal strontium barium niobate (SBN) are shown to provide electrically controlled diffraction. The diffraction can be temporally modulated by applying a time-varying electric field along the c-axis. This effect arises as the result of large nonlinear electro-optic and dielectric effects near the diffuse ferroelectric phase transition, which is around 30°C for SBN:75 and 70°C for SBN:61. Measurements are provided for SBN:75 that verify a simple model of the field-dependent diffraction.

Department of Applied Physics, Stanford University, Stanford, California 94305We report the observation of incident intensity and applied-field-induced increases in the absorption coefficient of Bi(12)SiO(20) at 514.5 nm. Absorption changes as large as 50% have been observed, but 10% is more typical. The main effect is thermal shifting of the absorption edge caused by ohmic heating from the photocurrent: Deltaalpha(T) = 0.0083 cm(-1) K(-1). In addition, there is a small absorption change proportional to the intensity alone that is approximately given by Deltaalpha(I) = 0.03 ln(I). We also report a linear decrease in the photoconductivity with temperature for T in the range 295-330 K.

Previous methods for analyzing double-exposed speckle photographs provide point-by-point velocity information by using two-dimensional Fourier analysis, or constant velocity contours by using spatial filtering techniques. A new method using an anamorphic optical system to measure one component of the velocity throughout a section of the flow is analyzed and demonstrated. A laser sheet, thin in the x direction and extended in the y direction, is used to probe a line of the photograph of which the anamorphic optical system forms a one-dimensional Fourier transform in the x direction and images the speckle pattern in the y direction for measuring the x-velocity component. This results in curved fringes, which have a local spacing inversely proportional to the x-velocity component at that point. Thus it is possible to measure a velocity component along a selected line in the flow. This differs from spatial filtering techniques that produce contours showing the points where a selected velocity occurs.

The first known experimental results of real-time optical defect enhancement of a periodic mask are reported. A low-intensity reference wave interferes with the Fourier transform of an object beam to form a hologram in a photorefractive crystal. The nonlinear properties of the crystal perform a filtering operation, and phase-conjugate readout results in a defect-enhanced image. Defects of size 10 microm x 100 microm have been easily detected with high signalto- noise ratio, and a discussion of performance limitations is presented.

We describe a novel procedure for obtaining enhanced nondestructive holographic readout in SBN, where the key new ingredient is utilization of degrees of freedom in polarization of the reconstruction beam. The effect also involves spatial frequency and the applied voltage during both the recording and the reconstruction. The reconstructed beam first drops in intensity but subsequently grows in strength above the starting value, approaching 100% efficiency in some cases. More than 6 h of continuous readout has been achieved, with efficiency remaining strong enough to give more than 10(9) 10-microsec readouts with signal-to-noise ratios exceeding 20 dB.

A novel switch geometry using photorefractive crystals has been demonstrated which has nondestructive readout and reduces the order of complexity of a non-blocking switching network. It is a routing full duplex design capable of handling the full bandwidth of the input signals. It is fully reconfigurable in times which depend principally upon the photorefractive material used and the intensity of the writing beams. The concept is applicable for use with a variety of photorefractive materials. The capacity of this switch has been calculated to be on the order of 100, based upon the sum of inputs and outputs, but is primarily limited by its simultaneous interconnectability. This limit is set by the number of gratings which can be stored in a single photorefractive crystal at one time. A demonstration of a 2 x 3 switch using BGO with 514nm writing beams and 633nm signal (readout) beams is descibed.