Self-trapping of optical vortices at the surface of an induced semi-infinite photonic lattice.

We demonstrate self-trapping of singly-charged vortices at the surface of an optically induced two-dimensional photonic lattice. Under appropriate conditions of self-focusing nonlinearity, a singly-charged vortex beam can self-trap into a stable semi-infinite gap surface vortex soliton through a four-site excitation. However, a single-site excitation leads to a quasi-localized state in the first photonic gap, and our theoretical analysis illustrates that such a bandgap surface vortex soliton is always unstable.

Quasi 3-dimensional optical trapping by two counter-propagating beams in nano-fiber.

Optical forces on a nanoparticle around an absorptive dielectric nano-fiber illuminated by two linear polarized counter-propagating beams were investigated. The results show the scattering force of the two beams causes the steady trapping along the fiber and the gradient force makes the trapping in the transverse plane of the nano-fiber. By altering the intensity ratio between the two incident beams and the polarization direction of the beams, manipulation along the nano-fiber and in the transverse direction can be realized, respectively.

Tuning of Bloch modes, diffraction, and refraction by two-dimensional lattice reconfiguration.

We demonstrate controlled excitation of Bloch modes and manipulation of diffraction and refraction in optically induced two-dimensional photonic lattices. Solely by adjusting the bias condition, the lattice structures can be reconfigured at ease, enabling the observation of transition between Bloch modes associated with different high-symmetry points of a photonic band, and interplay between normal and anomalous diffraction as well as positive and negative refraction under identical excitation condition.

Increased optical-damage resistance in tin-doped lithium niobate.

Applications of lithium niobate in nonlinear optics at high light intensities are seriously hampered by optical damage. Recent investigations have shown that Hf(4+) and Zr(4+) ions have some advantages in suppressing optical damage of LiNbO(3) with respect to Mg(2+). Here we present Sn-doped LiNbO(3) (Sn:LN).

Linear and nonlinear discrete light propagation in weakly modulated large-area two-dimensional photonic lattice slab in LiNbO3:Fe crystal.

A weakly modulated large-area two-dimensional square photonic lattice slab was fabricated through optical induction technique in a photorefractive photovoltaic LiNbO(3):Fe crystal. Bragg-matched diffraction technique was used to characterize the square photonic lattice slab. Interestingly, linear discrete diffraction typical for waveguide arrays was observed in such a square photonic lattice slab, indicating that the lattice slab can be viewed effectively as a one-dimensional waveguide array.

Fast responsive nonvolatile holographic storage in LiNbO(3) triply doped with Zr, Fe, and Mn.

Iron and manganese doubly doped LiNbO(3) (LN:Fe,Mn) has been suggested for nonvolatile photorefractive recording; however, its response time is still of the order of minutes. Here we present results on LiNbO(3) triply doped with zirconium, iron, and manganese (LN:Zr,Fe,Mn). The codoping with Zr eliminates undesirable intrinsic traps, which strongly enhances the charge transition speed.

Active chromatic control on the group velocity of light at arbitrary wavelength in benzocyclobutene polymer.

A novel method is proposed to generate slow and fast lights at arbitrary signal wavelength in benzocyclobutene (BCB) polymer, which eliminates the requirement on the optical nonlinearity or the resonant effect at the signal wavelength with the help of the thermo-optic nonlinear effect induced by a control beam at a different but fixed wavelength. The signal group velocity can be precisely tuned simply by scanning the position of the BCB sample along the light propagation direction. Another advantage is the ability to control chromatically the group velocity of the signal beam by adjusting the control beam in the BCB sample, which, in essence, is to control the refractive index change experienced by the signal beam.

Saddle solitons: a balance between bi-diffraction and hybrid nonlinearity.

We demonstrate self-trapping of light by simultaneously compensating normal and anomalous (saddle-shaped) diffractions with self-focusing and self-defocusing hybrid nonlinearity in optically induced ionic-type photonic lattices. Innovative two-dimensional gap solitons, named "saddle solitons," are established, whose phase and spectrum characteristics are different from all previously observed spatial solitons.

Light focusing by the unique dielectric nano-waveguide array.

The light focusing by using dielectric nano-waveguides array with its length in micron is investigated via the finite-difference time domain (FDTD) method. Simulated results show that the focal length depends on the length and the total width of the arrays and can be altered from tens of micron to wavelength order. Both TM and TE mode incident light can be focused by the array.

Optical trapping and manipulation of metallic micro/nanoparticles via photorefractive crystals.

A simple method to trap and manipulate metallic micro/nano-particles on the surface of photorefractive crystals is proposed. After inducing inhomogeneous charge density and space-charge fields in photorefractive crystals by non-uniform illumination, both uncharged and charged metallic particles can be trapped on the illuminated surface due to dielectrophoretic force and electrophoretic force, respectively. A transition from dielectrophoresis to electrophoresis is observed when manipulating nano-silver particles with high surface space-charge field.

Orientation-dependent excitations of lattice soliton trains with hybrid nonlinearity.

We demonstrate selective excitation of soliton trains residing in different gaps or within the same Bloch band of a new type of photonic lattice merely by changing the orientation of an input probe beam. A self-focusing and -defocusing hybrid nonlinearity as established in a nonconventionally biased photorefractive crystal leads to controlled soliton transitions from different band edges or subband edges, in good agreement with our theoretical analysis.

Efficient generation of propagating plasmons by electron beams.

We report highly efficient generation of propagating plasmons by electron beams in planar films, planar dielectric cavities, metallic wires, and nanoparticle waveguides. Electron-induced plasmon excitation is investigated in (1) gold thin films, both free-standing or supported on a silica substrate, (2) gold-silica-gold planar cavities, (3) gold nanowires, and (4) gold nanoparticle arrays. We obtain excitation yields as high as 10(- 2) plasmons per incoming electron over the visible and near-infrared range.

Real-time imaging of autofluorescence NAD(P)H in single human neutrophils.

Real-time detection of NAD(P)H is particularly important for understanding physiological activities of neutrophils. We scrutinize the performance of weak light detection systems with electron multiplying CCDs (EMCCDs) with regard to the feasibility of valid investigations by autofluorescence NAD(P)H in single human neutrophils. The low-noise amplification facility of EMCCDs is indeed just adequate to permit detection at an irradiation level where neither quenching nor phototoxic effects occur.

Exogenous nitric oxide-induced release of calcium from intracellular IP3 receptor-sensitive stores via S-nitrosylation in respiratory burst-dependent neutrophils.

PMA-induced respiratory burst neutrophils were exposed to exogenous nitric oxide (NO) donor sodium nitroprusside (SNP) to study the effect of NO on calcium signaling. A sharp rise of cytosolic calcium concentration ([Ca(2+)](c)) was triggered by 1mM SNP with and without external calcium. We found that GF 109203X, a specific inhibitor of protein kinase C, DPI, a putative inhibitor of the respiratory burst-generating NADPH oxidase, and 2-DG, a non-metabolizable analog of glucose, completely inhibited the SNP-induced rise of [Ca(2+)](c) in PMA-activated respiratory burst neutrophils.

Spatial frequency combs and supercontinuum generation in one-dimensional photonic lattices.

We experimentally demonstrate the formation of spatial supercontinuum and of spatial frequency combs in nonlinear photonic lattices. This process results from multiple four-wave mixing initiated by launching two Floquet-Bloch modes into a one-dimensional lattice. The dynamics of the waves is sensitively dependent on the transverse momentum difference between the two initial modes: when this momentum difference is commensurable with the lattice momentum the waves evolve into a frequency comb, whereas when it is incommensurable the waves evolve into a supercontinuum of spatial frequencies.

Higher-band gap soliton formation in defocusing photonic lattices.

We report on the experimental observation of higher-band gap solitons in a one-dimensional photonic lattice possessing a defocusing saturable nonlinearity. Pure Floquet-Bloch modes of the first three bands are excited using a prism-coupler setup, and spatial gap solitons of different width are formed, the latter property being related to the increasing anomalous diffraction in the three bands and the fixed value of the nonlinearity in our lithium niobate sample.

Self-trapping of optical vortices in waveguide lattices with a self-defocusing nonlinearity.

We demonstrate the self-trapping of single- and double-charged optical vortices in waveguide lattices induced with a self-defocusing nonlinearity. Under appropriate conditions, a donut-shaped single-charged vortex evolves into a stable discrete gap vortex soliton, but a double-charged vortex turns into a self-trapped quadrupole-like structure. Spectrum measurement and numerical analysis suggest that the gap vortex soliton does not bifurcate from the edge of the Bloch band, quite different from previously observed gap spatial solitons.

Elliptical discrete solitons supported by enhanced photorefractive anisotropy.

We demonstrate elliptical discrete solitons in an optically induced two-dimensional photonic lattice. The ellipticity of the discrete soliton results from enhanced photorefractive anisotropy and nonlocality under a nonconventional bias condition. We show that the ellipticity and orientation of the discrete solitons can be altered by changing the direction of the lattice beam and/or the bias field relative to the crystalline c-axis.

Optically induced transition between discrete and gap solitons in a nonconventionally biased photorefractive crystal.

We show that optically induced photonic lattices in a nonconventionally biased photorefractive crystal can support the formation of discrete and gap solitons owing to a mechanism that differs from the conventional screening effect. Both the bias direction and the lattice orientation can dramatically influence the nonlinear beam-propagation dynamics. We demonstrate a transition from self-focusing to -defocusing and from discrete to gap solitons solely by adjusting the optical-beam orientation.

Nonvolatile holographic storage of near-stoichiometric LiNbO3:Cu:Ce with green light.

The nonvolatile holographic storage of a near-stoichiometric LiNbO(3):Cu:Ce crystal with green light was investigated. With an increase in composition, improved nonvolatile holographic performance was obtained. The sensitivity S? of the near-stoichiometric LN(49.

Observation of dipole-like gap solitons in self-defocusing waveguide lattices.

We observe dipole-like gap solitons in two-dimensional waveguide lattices optically induced with a self-defocusing nonlinearity. Under appropriate conditions, two mutually coherent input beams excited in neighboring lattice sites evolve into a self-trapped state, whose spatial power spectrum and stability depend strongly on the initial excitation conditions. Our experimental observations are compared with numerical simulations.

Nonlinear spectrum reshaping and gap-soliton-train trapping in optically induced photonic structures.

We report the first theoretical prediction and experimental demonstration of gap soliton trains in a self-defocusing photonic lattice. Without a priori spectral or phase engineering, a stripe beam whose spatial power spectrum lies only in one transverse direction evolves into a gap soliton train with power spectrum growing also in the orthogonal direction due to nonlinear transport and spectrum reshaping. Our results suggest that, in nonlinear k-space evolution, energy can transfer not only between regions of normal and anomalous diffraction, but also from initially excited regions to initially unexcited regions.

Elliptical solitons in nonconventionally biased photorefractive crystals.

We theoretically predict and experimentally observe the two-dimensional (2-D) bright solitons in a nonconventionally biased strontium barium niobate (SBN) crystal. A theory describing light propagating in an SBN crystal with a bias field along an arbitrary direction is formulated. Then the existence of 2-D bright solitons in such a crystal is numerically verified.

Three-photon indirect sensitization in green upconversion luminescence of Er/Tm codoped NaY(WO(4))(2) crystal.

Upconversion spectra of Er/Tm codoped NaY(WO(4))(2) crystal excited by 974nm laser is investigated. Intensive 520nm/550nm and 800nm emissions are observed. Three-photon process at high pumping power is presented in the green upconversion.