Notes: Selected as a "editor suggestion" and highlighted in
PhysicalReviewFocus: http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2012/PhysicsFocus_2012_5_3.pdf
Nature Physics: http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2012/NatPhys_Millikan.pdf
Nature Materials: http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2012/Onebyone.pdf
Nanometer.ru: http://www.nanometer.ru/2012/02/20/13297342298428_269921.html
Belgian Magazines http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2012/EOS_Millikan.pdf
http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2012/Knack_Millikan.pdf
Abstract: Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the electrophoretic mobility (EPM) of single optically trapped yeast cell under hyperosmotic stress conditions using optical tweezers combined with a position detector. We studied the dynamics of the EPM stress response for the cells taken at different phases of the cell cycle.
Abstract: Raman spectra from single DNA molecules in their natural aqueous environment are presented. A
DNA molecule that is anchored between two optically trapped dielectric beads is suspended in a
solution with nanosized silver colloid particles. The nonspeciï¬c binding of the metal to the DNA
enhances the Raman scattering that is excited by a near-infrared beam. A Raman spectrum is ï¬rst
recorded followed by a force-extension curve that veriï¬es the presence of a single DNA
molecule.
Abstract: An understanding of the mechanisms of drug diffusion and uptake through cellular membranes is critical for elucidating drug action and in the development of effective drug delivery systems. We study these processes for emodin, a potential anticancer drug, in live cancer cells using surface-enhanced Raman scattering. Micrometer-sized silica beads covered by nanosized silver colloids are passively embedded into the cell and used as sensors of the drug. We demonstrate that the technique offers distinct advantages: the possibility to study the kinetics of drug diffusion through the cellular membrane toward specific cell organelles, the detection of lower drug concentrations compared to fluorescence techniques, and less damage imparted on the cell.
Abstract: Raman spectroscopy was used to monitor changes in the oxygenation state of human red blood cells while they were placed under mechanical stress with the use of optical tweezers. The applied force is intended to simulate the stretching and compression that cells experience as they pass through vessels and smaller capillaries. In this work, spectroscopic evidence of a transition between the oxygenation and deoxygenation states, which is induced by stretching the cell with optical tweezers, is presented. The transition is due to enhanced hemoglobin-membrane and hemoglobin neighbor-neighbor interactions, and the latter was further studied by modeling the electrostatic binding of two of the protein structures.
Abstract: The momentum transfer to a scatterer from fluorescence photons was detected using an optical system that permits one to simultaneously measure the radiation force exerted on and fluorescence emission from the scatterer. The core of this technique is a partially metal covered dielectric bead optically trapped in a liquid with dye molecules. Fluorescence emission from the volume that includes the bead is measured simultaneously with the Brownian motion of the bead. The perturbed motion of the bead is a result of photon momentum transfer from the fluorescence of the dye to the trapped scatterer. The bead position fluctuations indicate the presence of the fluorescence and its bleaching nature. The results demonstrate the capability of the photonic force microscopy technique to be a complement to spectroscopy in the study of optical processes.
Notes: Featured in Physical Review Focus: http://focus.aps.org/story/v24/st12
Abstract: Surface enhanced Raman scattering (SERS) is studied from optically trapped dielectric spheres partially covered with silver colloids in a solution with SERS active molecules. The Raman scattering and Brownian motion of the sphere are simultaneously measured to reveal correlations between the enhancement of the Raman signal and average position of the sphere. The correlations are due to the momenta transfer of the emitted Raman photons from the probe molecules. The addition of a mechanical force measurement provides a different dimension to the study of Raman processes.
Notes: Featured in Physical Review Focus: http://focus.aps.org/story/v24/st12
Abstract: We propose a technique that permits one to increase by one order of magnitude the detection range of position sensing for the photonic force microscope with quadrant photodetectors (QPDs). This technique takes advantage of the unavoidable cross-talk between output signals of the QPD and does not assume that the output signals are linear in the probe displacement. We demonstrate the increase in the detection range from 150 to 1400 nm for a trapped polystyrene sphere with radius of 300 nm as probe.
Abstract: Usually in the presence of a background noise an increased effort put in controlling a system stabilizes its behavior. Rarely it is thought that an increased control of the system can lead to a looser response and, therefore, to a poorer performance. Strikingly there are many systems that show this weird behavior; examples can be drawn form physical, biological, and social systems. Until now no simple and general mechanism underlying such behaviors has been identified. Here we show that such a mechanism, named stochastic resonant damping, can be,provided by the interplay between the background noise and the control exerted on the system. We experimentally verify our prediction on a physical model system based on a colloidal particle held in an oscillating optical potential. Our result adds a tool for the study of intrinsically noisy phenomena, joining the many constructive facets of noise identified in the past decades-for example, stochastic resonance, noise-induced activation; and Brownian ratchets.
Notes: Times Cited: 5
Notes: Nature Physics featured this publication: "Soft Grip" http://www.nature.com/nphys/journal/v4/n6/full/nphys995.html Science News featured this publication: "Less is more" http://users.icfo.es/Dmitri.Petrov/Science%20News%20-%20Less%20Is%20More.html
Abstract: We detected the second-order nonlinear response from single isolated spheres comprised from a centrosymmetric material but covered by a layer of a material with strong second-order nonlinear properties and isolated from an ensemble by the optical trapping technique. We show that when large size parameter spheres are used, the measured second-harmonic efficiency deviates strongly from the prediction of the nonlinear Rayleigh scattering theory. Our results are in very good agreement with the predictions from the exact nonlinear Mie scattering theory. (C) 2008 Optical Society of America.
Abstract: We suggest an approach to microrheology based on optical traps capable of measuring fluid fluxes around singular points of fluid flows. We experimentally demonstrate this technique, applying it to the characterization of controlled flows produced by a set of birefringent spheres spinning due to the transfer of light angular momentum. Unlike the previous techniques, this method is able to distinguish between a singular point in a complex flow and the absence of flow at all; furthermore it permits us to characterize the stability of the singular point.
Abstract: Using optical tweezers combined with luminescence measurements we detected the optical field around two optically trapped silica microspheres partially covered by metal. By monitoring the luminescence of rhodamine 6G we were able to observe an increase of the local field intensity owing to the coupling of the local surface plasmons at the surfaces of two spheres.
Abstract: We present a quantitative analysis of 2D surface plasmon based optical tweezers able to trap microcolloids at a patterned metal surface under low laser intensity. Photonic force microscopy is used to assess the properties of surface plasmon traps, such as confinement and stiffness, revealing stable trapping with forces in the range of a few tens of femtonewtons. We also investigate the specificities of surface plasmon tweezers with respect to conventional 3D tweezers responsible for their selectivity to the trapped specimen's size. The accurate engineering of the trapping properties through the adjustment of the illumination parameters opens new perspectives in the realization of future optically driven on-a-chip devices.
Abstract: The photonic force microscope (PFM) is an opto-mechanical technique that uses an optically trapped probe to measure forces in the range of pico to femto Newton. For a correct use of the PFM, the force field has to be homogeneous on the scale of the Brownian motion of the trapped probe. This condition implicates that the force field must be conservative, excluding the possibility of a rotational component. However, there are cases where these assumptions are not fulfilled. Here, we show how to expand the PFM technique in order to deal with these cases. We introduce the theory of this enhanced PFM and we propose a concrete analysis workflow to reconstruct the force field from the experimental time series of the probe position. Furthermore, we experimentally verify some particularly important cases, namely, the case of a conservative and of a rotational force field.
Abstract: An optically trapped particle is an extremely sensitive probe for the measurement of pico- and femto-Newton forces between the particle and its environment in microscopic systems (photonic force microscopy). A typical setup comprises an optical trap, which holds the probe, and a position sensing system, which uses the scattering of a beam illuminating the probe. Usually the position is accurately determined by measuring the deflection of the forward-scattered light transmitted through the probe. However, geometrical constraints may prevent access to this side of the trap, forcing one to make use of the backscattered light instead. A theory is presented together with numerical results that describes the use of the backscattered light for position detection. With a Mie-Debye approach, we compute the total (incident plus scattered) field and follow its evolution as it is collected by the condenser lenses and projected onto the position detectors and the responses of position sensitive detectors and quadrant photodetectors to the displacement of the probe in the optical trap, both in forward and backward configurations. We find out that in the case of backward detection, for both types of detectors the displacement sensitivity can change sign as a function of the probe size and is null for some critical sizes. In addition, we study the influence of the numerical aperture of the detection system, polarization, and the cross talk between position measurements in orthogonal directions. We finally discuss how these features should be taken into account in experimental designs. (C) 2007 American Institute of Physics.
Abstract: The cytoskeleton provides the backbone structure for the cellular organization, determining, in particular, the cellular mechanical properties. These are important factors in many biological processes, as, for instance, the metastatic process of malignant cells. In this paper, we demonstrate the possibility of monitoring the cytoskeleton structural transformations in optically trapped yeast cells ( Saccharomyces cerevisiae) by tracking the forward scattered light via a quadrant photodiode. We distinguished normal cells from cells treated with latrunculin A, a drug which is known to induce the actin-cytoskeleton depolymerization. Since the proposed technique relies only on the inherent properties of the optical trap, without requiring external markers or biochemical sensitive spectroscopic techniques, it can be readily combined with existing optical tweezers setups. (C) 2007 Optical Society of America
Abstract: A statistical analysis of the movement of an optically trapped sub-micron sphere in an external rotational force field permits us to measure the torque exerted on the sphere. (C) 2006 Optical Society of America
Abstract: The photonic force microscope (PFM) is an opto-mechanical technique that uses an optically trapped probe to measure forces in the range of pico to femto Newton. For a correct use of the PFM, the force field has to be homogeneous on the scale of the Brownian motion of the trapped probe. This condition implicates that the force field must be conservative, excluding the possibility of a rotational component. However, there are cases where these assumptions are not fulfilled. Here, we show how to expand the PFM technique in order to deal with these cases. We introduce the theory of this enhanced PFM and we propose a concrete analysis workflow to reconstruct the force field from the experimental time series of the probe position. Furthermore, we experimentally verify some particularly important cases, namely, the case of a conservative and of a rotational force field.
Abstract: We compare the sensitivity of the Photonic Force Microscope for the forward-scattering and backward-scattering geometries, calculating the total-scattered electromagnetic field from a dielectric bead in an optical trap using a Mie-Debye approach. (C) 2006 Optical Society of America
Abstract: A flexible pressure sensor based on a bi layer (BL) organic film has been fabricated. The conducting microcrystalline layer of an organic molecular conductor is used as a high sensitive piezoresistive material to detect and transmit pressure data. The polymeric matrix serves as both diaphragm and support for the placement of the conducting layer over it. Remarkably, the different electronic circuits can be directly designed on the conducting microcrystalline layer using a very simple technique. The sensors based on BL films can be employed in innovative applications such as smart clothing and robotic interfaces.
Abstract: In this paper we discuss a state-of-the-art optical technique which combines Raman microspectroscopy and optical trapping. This technique permits one to study Raman spectra of aerosol particles, gas bubbles and cells that normally live in suspension and it opens the way to acquire information that otherwise would be inaccessible for this class of microparticles.
Abstract: We describe a new facile chemistry-based technique for patterning films of organic conductors on a polymeric substrate that consists of directly writing on the organic conducting surface using a local heat source such as a laser beam.
Abstract: The combination of Raman spectroscopy and Optical Tweezers has been used to trap living cells and collect information about their biochemical state. Cells can continue living in such traps for periods of hours, allowing acquisition of time resolved Raman spectra. However no spatial information can be acquired as the cells continue to rotate and move in the single beam trap. Here we describe the development of Holographic Optical Tweezers (HOT) for the controlled movement of floating cells in order to construct their Raman images. Instead of a single trap, rapidly programmable multiple trapping points can be produced around the periphery of the cells to impede the rotational motion of the cell. By trapping and scanning the cell using HOT relative to a fixed Raman exciting laser, a point by point image of the cell can be constructed. We use an interactive program that permits us to position the trapping points relative to the live image feed we see from the microscope, using point and click. To demonstrate the possibilities of this technique images are shown of floating Jurkat cells.
Abstract: Living cells show a variety of morphological traits upon which numerous identification techniques have already been developed. However most of them involve lengthy biochemical procedures and can compromise the viability of the cell. We demonstrate a method to differentiate cells only on the basis of its trapping dynamics while it is being drawn into an optical trap (Optical Trapping Dynamics). Since it relies only on the inherent properties of the optical trap, without requiring external markers or biochemically sensitive spectroscopic techniques, it can be readily combined with existing optical tweezers setups. We applied it to the study of the yeast cell-cycle stages, showing, in particular, how it can be amenable for the measurement of the budding index of a cell population.
Abstract: We optically trapped a single yeast cell for up to 3 h and monitored the changes in the Raman spectra during the lag phase of its growth and the G(1) phase of its cell cycle. A non-budding cell (corresponding either to the G(0) or G(1) phase) was chosen for each experiment. During the lag phase, the cell synthesises new proteins and lipids and the observed behaviour of the peaks corresponding to these constituents as well as those of RNA served as a sensitive indicator of the adaptation of the cell to its changed environment. Temporal behaviour of the Raman peaks observed was different in the lag phase as compared to the late lag phase. Two different laser wavelengths were applied to study the effect of long-term optical trapping on the living cells. Yeast cells killed either by boiling or by a chemical protocol were also trapped for a long time in a single beam optical trap to understand the effect of optical trapping on the behaviour of observed Raman peaks. The changes observed in the Raman spectra of a trapped yeast cell in the late G(1) phase or the beginning of S phase corresponded to the growth of a bud. Copyright (C) 2006 John Wiley & Sons, Ltd.
Abstract: One of the most promising ways to study the biochemistry of single floating cells is to combine the techniques of optical tweezers and Raman spectroscopy (OTRS). This can reveal the information that is lost when ensemble averages are made over cell populations, like in biochemical assays. However, the interpretation of the acquired data is often ambiguous. Indeed, the trapped living cell continues to move and rotate in the optical trap not only because of the Brownian motion, but also because of its inherent biological motility and the variation of its shape and size. This affects both Rayleigh and Raman light scattering. We propose the use of Rayleigh scattering to monitor the growth of a single optically trapped yeast cell, while OTRS measurements are being performed. For this purpose, we added a quadrant photodiode to our OTRS setup. The cell orientation in the optical trap is shown to vary as the cell growth proceeds, especially when it becomes asymmetrical (budding) or it changes its size or shape considerably (living and growing cell). Control experiments, performed using heat-treated cells and polystyrene beads, confirm that this behavior is a consequence of the cell growth. These measurements have to be taken into account in the interpretation of Raman spectra so as not to incorrectly attribute variations in the spectra to change in the biochemical constituents of the cell if they are in fact due to a change of the orientation of the cell in the trap.
Abstract: We report the first experimental observation of momentum transfer from a surface plasmon to a single dielectric sphere. Using a photonic force microscope, we measure the plasmon radiation forces on different polystyrene beads as a function of their distance from the metal surface. We show that the force magnitude at resonance is strongly enhanced compared to a nonresonant illumination. Measurements performed as a function of the probe particle size indicate that optical manipulation by plasmon fields has a strong potential for optical sorting.
Abstract: We report the statistical analysis of the movement of a submicron particle confined in a harmonic potential in the presence of a torque. The absolute value of the torque can be found from the auto- and cross-correlation functions of the particle's coordinates. We experimentally prove this analysis by detecting the torque produced onto an optically trapped particle by an optical beam with orbital angular momentum.
Notes: Times Cited: 15
Phys. Rev. Focus featured this paper http://users.icfo.es/Dmitri.Petrov/Personal_DVP/2006/Papers/PhysRevFocus2006.pdf
Abstract: We analyze the forward scattered light from a single optically trapped cell during its growth. We show that the cell continues adjusting itself to the applied optical force because of the growth processes, and hence it keeps changing its orientation in the trap. We point out the importance of taking this variation into account in the interpretation of spectroscopic data. This method can also be used as a means for cell identification and cell sorting. (c) 2006 American Institute of Physics.
Abstract: We report on the study of the radiation forces exerted on a Rayleigh dielectric particle by a patterned optical near-field landscape at an interface decorated with resonant gold nanostructures. This configuration allows for the generation of a large array of surface subwavelength optical traps from an extended collimated beam, which may be of interest for parallel optical manipulation and sorting of submicrometer objects. (c) 2005 Optical Society of America
Abstract: We describe the use of dual optical tweezers to manipulate micron-size particles in and out of the focus of a confocal Raman microscope. One of the beams excites the Raman spectrum while the second tweezers improves the sensitivity of the technique and also allows for the manipulation of the environment of the trapped objects. We concentrated on optimising the alignment of both trapping and Raman excitation beams and on the background subtraction method. Even at the low trapping/excitation powers used a single living cell could be trapped and monitored for over 2 h without incurring damage. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: Multiple beam tweezers are demonstrated for Raman spectroscopy of living cells. Results are presented for time resolved Raman. Data for spatially resolved Raman is shown and holographic tweezers for cell imaging is proposed. (c) 2005 Optical Society of America.
Abstract: Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the Raman spectra of optically trapped Saccharomyces cerevisiae yeast cell under normal, heat-treated, and hyperosmotic stress conditions. It is shown that when glucose was used to exert hyperosmotic stress, two chemical substances-glycerol and ethanol-can be monitored in real time in a single cell.
Abstract: Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the Raman spectra of optically trapped Saccharomyces cerevisiae yeast cell under normal, heat-treated, and hyperosmotic stress conditions. It is shown that when glucose was used to exert hyperosmotic stress, two chemical substances-glycerol and ethanol-can be monitored in real time in a single cell.
Abstract: Raman imaging can yield spatially resolved biochemical information from living cells. To date there have been no Raman images published of cells in suspension because of the problem of immobilizing them suitably to acquire space-resolved spectra. In this paper in order to overcome this problem the use of holographic optical tweezers is proposed and implemented, and data is shown for spatially resolved Raman spectroscopy of a live cell in suspension.
Abstract: The trapping of micro-objects by optical radiation forces, so-called optical tweezers, has become widely used in physical, chemical and biological experiments where accurate and non-invasive manipulation is required. Recent advances in beam shaping render it possible for instance to rotate or to dynamically manipulate independently several elements. Today, one of the remaining challenges of conventional optical tweezers is the direct manipulation of systems with sizes belonging to the subwavelength or Rayleigh regime. Indeed, the diffraction limit prevents in that case from achieving a commensurable trapping volume and thus does not allow for minimizing the fluctuations in position of the trapped object due to its strong Brownian motion. In order to overcome this limitation, it has been proposed to use evanescent fields instead of the usual propagating fields.
Abstract: Multiple beam tweezers are demonstrated for Raman spectroscopy of living cells. Results are presented for time resolved Raman. Data for spatially resolved Raman is shown and holographic tweezers for cell imaging is proposed. (c) 2005 Optical Society of America.
Abstract: We report the first experimental observation, to our knowledge, of the self-trapping of light in walk-off-compensating optical tandems. The experiment was conducted with picosecond light pulses in a ten-plate optically contacted tandem made of potassium titanyl phosphate prepared for phase matching along a special geometry featuring a huge local walk-off. The observation should open the door to the exploration of multicomponent soliton formation in new classes of materials and settings. (C) 2004 Optical Society of America.
Abstract: We propose a novel method to efficiently produce light beams with radial, azimuthal, and hybrid polarization, through a few-mode fiber excited by a Laguerre-Gaussian beam. With different input polarization we can selectively excite different combinations of modes from the LP11 group. We propose to show how to transform the output beam into a cylindrical vector beam in free-space through various polarization transformations. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: Gradient radiation forces exerted by strongly focused cylindrical vector beams of radial and azimuthal polarizations on dielectric spheres of different radii and refractive indices were calculated. The effect of longitudinal and transversal components of the focused electrical field on trapping properties was studied. Experiments on optical trapping were performed using low-mode optical fiber excited with Laguerre-Gaussian beam as a source of the trapping beams.
Abstract: We demonstrate an experimental scheme that allows the elucidation of the orbital angular momentum discrete spectrum of an arbitrary light signal. The orbital angular momentum spectrum is represented in a Laguerre-Gaussian mode base, and the spectral components are resolved in the frequency domain by exploiting the Doppler frequency shift that is imparted to rotating light beams. (C) 2003 Optical Society of America.
Abstract: We report the observation of deflection of optical solitons generated in the frequency doubling of light beams containing edgelike topological amplitude and phase dislocations. The angular deflection of the solitons was found to be controllable through the position of the dislocation. The experiments were conducted near phase matching in a bulk potassium titanyl phosphate crystal pumped with picosecond light pulses at 1064 nm.
Abstract: We report the first experimental observation of self-focusing in walk-off compensanting optical tandems. The observation should open the door to the exploration of soliton formation in new classes of materials and settings.
Abstract: A phenomenon of a strong irreversible variation of the refractive index (Deltan approximate to - 0,2) in a subsurface layer of the lithium niobate crystal has be en observed. The effect arises under the strong absorption of high-power radiation with wavelength 248 run of KrF excimer laser. The characteristics of the subsurface photorefractive effect (SPRE) were identified by using the data on measurements of the reflection coefficient of a crystal and of the diffraction efficiency of a recorded phase grating. About 40% of niobium and oxygen atoms has been found to be displaced from the lattice points in the 350 50 A subsurface layer. This phenomenon was used for creation of some integrated optics elements.
Abstract: The first hyperpolarizability of aqueous suspensions of polyphosphate stabilized US nanocrystals of different mean sizes and of CdxZn1-xS nanocrystals (x = 0, 0.25, 0.75, 1) was determined by the hyper-Rayleigh scattering technique. We report the first experimental observation that the first hyperpolarizability decreases as the band gap energy increases. This is ascribed to the decrease of the resonance enhancement. The surface modification of 9 nm US nanocrystals with OH- increases the first hyperpolarizability by a factor 1.7. This is explained in terms of the higher polarizability of the surface terminating groups after the OH- modification. Finally, we have also established the size dependence of the first hyperpolarizability for US nanocrystals. Although it increases with the particle size, its values normalized per US pair increase with decreasing of size, leading to an enhancement by 1 order of magnitude for 2 nm particles in comparison with bulk. This is explained by assuming the enhancement of both the bulk contribution from the noncentrosymmetric nanocrystal core and the surface contribution. The enhancement of the bulk contribution is ascribed to quantum confinement effects on the normalized oscillator strengths. The surface contribution becomes more relevant as the size decreases and may be enhanced by several effects, especially surface polarization. A two-level model can explain both the band-gap and the size dependences.
Abstract: We report what is believed to be the first experimental observation of spontaneous nucleation of arrays of optical vortices in the process of second-harmonic generation in a crystal with moderate Poynting vector walk-off, pumped with focused beams containing screw phase dislocations. Our experiments were conducted in lithium triborate under conditions of small-efficiency second-harmonic generation pumped by nanosecond pulses at 1064 nm. (C) 2002 Optical Society of America.
Abstract: We report what we believe to be the first experimental demonstration of the dependence of hyper-Rayleigh scattering (HRS) (fundamental wavelength of 1064 nm) and, hence, the first hyperpolarizability in optically pumped p-nitroaniline (PNA) molecules on the energy of pump photons, (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: Theoretical study of the hyperpolarisabilities beta and gamma of aniline oligomers is presented. The results obtained for beta at the AM1/TDHF level are promising for the emeraldine form, indicating a potential use as a second-order nonlinear optical material. The calculations of static cubic hyperpolarisability of trimers agree with the experimentally observed trends for polyaniline. (C) 2002 Published by Elsevier Science B.V.
Abstract: We calculated the first hyperpolarizability of the molecules with some fraction of both ground and excited state populations. We used a numerical procedure employed widely known software. The comparison with experimental data for para-nitroaniline molecule obtained by the Hyper-Rayleigh technique is done. (C) 2002 Published by Elsevier Science B.V.
Abstract: The first hyperpolarizability beta per monomeric residue of polyaniline in three oxidation states and in the doped emeraldine salt form was determined by hyper-Rayleigh scattering. Multiphoton induced fluorescence was observed and, together with light absorption at the fundamental (omega) and double (2omega) frequencies was taken into account in the calculation of beta.
Abstract: Diffraction gratings were recorded both optically and interferometrically in dichromated poly(vinyl alcohol) (DCPVA) films by means of dichromate photoreduction. Aniline was used as a chemical developer, through in situ polymerization in the unreduced parts of the film. The resulting composite material shows the optical and chemical properties of polyaniline and the mechanical resistance of PVA. Characterization of the gratings gave a line width of 12.2 mum and a diffraction efficiency of 32%. Uv-vis spectroscopy was used to study dichromate photoreduction and the optical properties of the composite..
Abstract: In a linear medium an optical vortex induces the splitting of an edge dislocation into vortices of both topological charges. Their positions and number depend on which of the phase dislocations is shifted from the center of the host beam. Violations of the charge conservation law are discussed.
Abstract: The interaction of a vortex and an edge phase dislocation nested in a Gaussian beam by its free space propagation is studied experimentally and theoretically in the paraxial regime. Ibis interaction induces the nucleation of additional vortices of both topological charges. Their positions and number depend on which of the phase dislocations is shifted from the center of the host beam. The interaction of noncoaxial light beams containing these phase dislocations is also reported.
Abstract: The interaction of a vortex and an edge phase dislocation nested in a Gaussian beam by its free-space propagation is studied experimentally and theoretically in the paraxial regime. This interaction induces the nucleation of additional vortices of both topological charges. Their positions and number depend on the initial shift of the edge dislocation relative to the vortex. (C) 2001 Published by Elsevier Science B.V.
Abstract: Experimental and theoretical results on second harmonic generation with fundamental beams containing both a vortex and an edge phase dislocations are reported. The 3D trajectories in the fundamental and second harmonic beams are calculated for different distances between the dislocations in the input beam. It is shown that each phase dislocation in the second harmonic beam appears as a result of the joint actions of all phase dislocations in the fundamental beam. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: Experimental and theoretical results on second harmonic (SH) generation with fundamental beams containing edge phase dislocations are reported. If the input edge dislocation is on-axis of the host Gaussian beam, no edge dislocations are generated in the SH beam. However, this beam contains one edge dislocation if the edge dislocation in the input beam is off-axis. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: The first hyperpolarizability of nanocrystalline CdS particles (mean diameters of 2.0, 5.6 and 9.1 nm) was measured by the hyper-Rayleigh scattering technique. The results show that the first hyperpolarizability per CdS pair increases with decreasing particle size. This is ascribed to quantum confinement effects on the oscillator strengths. These effects lead to an enhancement by one order of magnitude in the first hyperpolarizability of 2 nm CdS particles, in comparison with bulk CdS. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Abstract: We present experimental results on the transfer of the orbital angular momentum of light to a system of cold cesium atoms; A nondegenerate four-wave mixing process was used as an indirect tool to observe this transfer. Our experiments show, in particular, that the orbital angular momentum of light can be transferred, via optical pumping in the cold atomic sample, from one beam to another oscillating at a different frequency.
Abstract: We investigate the evolution of vortex wave front dislocations in multiple-wave second-harmonic generation processes in quadratic nonlinear media. Vortices nested in finite-size host beams are shown to nucleate and to annihilate in pairs, and to move across the transverse wave front during the beam evolution. A closed-form model that holds under conditions of negligible-depletion of the pump beam is developed to describe the vortex dynamics in order to predict the number of vortices present in the wave fronts of the beams at any instance of the propagation. Results are compared with numerical simulations of the full governing equations and with experimental observations. Limitations of the model an outlined. (C) 1999 Elsevier Science B.V. All rights reserved.
Abstract: The combined effects of diffraction and Poynting vector walk-off in second-harmonic generation with pump beams that contain screw phase dislocations is addressed for what is believed to be the first time. We predict the spontaneous nucleation of multiple Vortex twins whose subsequent explosion can yield quasi-aligned patterns of single-charge vortices. (C) 1999 Optical Society of America OCIS codes: 190.4410, 050.1940, 190.7070, 140.3300.
Abstract: We find families of optical bright, vortex solitary waves in bulk quadratic nonlinear media under conditions for type II second-harmonic generation. We study the main properties of the families of solitary waves, including their stability. The vortex solitary waves are found to be azimuthally unstable and their decay into sets of stable spatial solitons is shown. We calculate the growth rates of the possible azimuthal perturbations with different azimuthal index and show how those affect the pattern of output light. Numerical simulations to check the predictions of the stability analysis are also reported. (C) 1998 Elsevier Science B.V.
Abstract: We describe the principle of operation of a new class of optical devices operating in quadratic non-linear media that mix wave front topological charge dislocations nested in focused light beams and produce certain patterns of bright spatial solitons. Central to the device behaviour is the orbital angular momentum of the light beams.
Abstract: We report the observation of the nucleation of pairs of screw dislocations of opposite topological charges in second-harmonic generation processes in quadratic nonlinear media. The observation provides evidence about the conservation and evolution of the topological charge of light waves parametrically interacting in the nonlinear medium in the dynamical regime explored. [S1063-651X(98)12111-6].
Abstract: We find families of vortex solitary waves in bulk quadratic nonlinear media under conditions for second-harmonic generation. We show that the vortex solitary waves are azimuthally unstable and that they decay into sets of stable spatial solitons. We calculate the growth rates of the azimuthal perturbations and show how those affect the pattern of output light. (C) 1998 Optical Society of America.
Abstract: We report what is believed to be the first experimental demonstration of the azimuthal self-breaking of intense beams containing a vortex phase dislocation into sets of optical spatial solitons in a quadratic nonlinear material. The observations were performed in a KTP crystal. (C) 1998 Optical Society of America.
Abstract: Second-harmonic generation of light in bulk quadratic non-linear media with intense input beams containing phase dislocations is studied numerically under conditions for Type I phase-matching. We investigate how, above a threshold light intensity, the input beams self-split along the azimuthal direction into a pattern of separate beams which then form a set of spatial solitons. The mechanism of such a behaviour is the azimuthal modulational instability of the ring-shaped, mutually trapped fundamental and second-harmonic beams containing the phase dislocations.
Abstract: The authors investigate numerically the process of second-harmonic generation of light in bulk quadratic nonlinear media with input beams containing phase dislocations. The authors find that above a threshold light intensity, the input beams self-split into several pieces along the azimuthal direction and form sets of spatial solitons.
Abstract: Second-harmonic generation (SHG) by means of radiation modes (the Cerenkov-type radiation scheme) in an anisotropic optical waveguide by off-axis propagation has been studied theoretically. If the second-harmonic wave is a leaky wave of the waveguide, the Cerenkov type SHG efficiency may be comparable with the efficiency of the guided-mode-guided-mo de SHG without critical control of the wave-vector-matching condition. The model presented predicts a strong modification of the radiation field by a change of the interaction length. A numerical simulation of the proposed type of SHG in a graded-index waveguide on the X-cut surface of LiNbO3 is made. (C) 1997 Optical Society of America.
Abstract: We performed Z-scan measurements to investigate the optical nonlinearity of poly(3-hexadecylthiophene) in a chloroform solution. Values for the real and the imaginary parts of the nonlinear susceptibility were obtained for solutions with various polymer concentrations. The nonlinear-optical properties were studied as a function of polymer concentration and light intensity from which saturation of nonlinear refraction and saturated absorption were observed. The saturation intensity was determined, and the corresponding values are presented for all concentrations studied. Time-resolved measurements of the nondiagonal part of nonlinear susceptibility are also presented. (C) 1997 Optical Society of America.
Abstract: The near-band-gap low-temperature photoluminescence (PL) in a pure film of GaAs in the presence of surface acoustic waves (SAW) has been studied experimentally. The complex behavior of the PL peak intensities with SAW power in the excitonic and acceptor spectral regions results from a charge bunching due to the piezoelectric field of SAW. (C) 1997 American Institute of Physics.
Abstract: It is shown that induced asymmetry and anisotropy of the refractive index change in a conventional scheme of an electro-optical guided-wave modulator produce a lateral shift of the guided mode field maximum and a voltage-dependent leakage of the guided-mode energy. This behavior of the transverse profile of the electromagnetic field may be exploited to build a channel waveguide amplitude modulator.
Abstract: In this work, it is shown experimentally that optical beams that contain a phase dislocation can be generated with a laser oscillating in the fundamental mode and a cylindrical-lens mode converter. (C) 1997 Elsevier Science B.V.
Abstract: We investigate the propagation of intense light beams in bulk quadratic nonlinear crystals under conditions for second-harmonic generation. We show numerically that input light beams with a spiral phase dislocation self-split in the crystal into several spatial solitons. The number and the pattern of output solitons can be controlled by the material and wave parameters involved and in particular by the input-light intensity and by the topological charge of the dislocation. (C) 1997 Optical Society of America.
Abstract: A novel waveguide directional coupler configuration consisting of a slab of anisotropic material with identical waveguides on both surfaces is proposed. By off-axis propagation the radiative part of a leaky wave provides a coupling between waveguides, The length of total power transfer depends on the slab's thickness and propagation angle relative to the optic axis.
Abstract: Spatial modification of a Gaussian beam reflected from a single interface and a thin film with intensity-dependent refractive index and absorption coefficient is studied theoretically. The measurement of this modification by different positions of the nonlinear surface with respect to the beam waist (the modified Z-scan technique) can be used to study nonlinear optical properties. For a single interface the measurements permit the nonlinear parameters to be determined unambiguously. For a thin film the multiple internal reflections are important, and the value and the sign of nonlinear refraction and absorption coefficients cannot be uniquely found. (C) 1996 Optical Society of America
Abstract: A direct numerical procedure is presented to evaluate the field distribution of radiation modes in an anisotropic optical waveguide with arbitrary ordinary and extraordinary index profiles.
Abstract: The modification of a Gaussian beam profile caused by the electronic contribution to the surface nonlinear absorption of a semiconductor doped glass was measured. The reflection Z-scan and transmission Z-scan techniques used allow to observe differences between the bulk and the surface nonlinear properties.
Abstract: Guided and radiation modes in a nonlinear planar graded-index waveguide are considered. The numerical results (effective refractive index versus mode power and mode field distributions) are presented. The intensity-dependent cutoff value for the radiation modes is observed. A dark fundamental wave at the smooth interface of the nonlinear substrate and waveguide region is studied. The discrete spectrum of the solutions that describe quasi-guided modes with a constant (nonzero) value of the field in the substrate is found.
Abstract: A phase shift for the input beam induced by cascaded second order nonlinear processes in structures with periodical modulation of linear and nonlinear susceptibilities is considered. Numerical examples are tabulated for LiNbO3/H+:LiNbO3, GaAs/Ga0.2Al0.2As, and GaP/AlP periodical structures.
Abstract: A time-resolved anisotropic configuration exploiting the Z-scan technique in a one color pump-and-probe arrangement was implemented to measure the time response and the value of the nondiagonal component of the third-order nonlinear susceptibility of a chloroform solution of poly (3-hexadecylthiophene). In addition, an all-optical Kerr gate with picosecond response using the polymeric solution was implemented. (C) 1996 American Institute of Physics.
Abstract: The nonlinear-optical properties of a semi-interpenetrating polymer network of poly(vinyl alcohol) glutaralde-hyde-polyaniline were studied. Large (>/=10(-12) cm(2)/W) and fast (<50 ps) refractive optical nonlinearites were observed. The potential of this novel material for photonic applications is evaluated.
Abstract: We report the successful fabrication of planar waveguides in rare-earth doped fluoroindate glass substrates. A new procedure for waveguide fabrication using a thermally evaporated AgF nonmetallic film was developed. The refractive index changes of more than 0.03, associated to low propagation losses achieved, open new perspectives and show the potentiality of using this glass family toward further developments in fabrication and design of integrated optical devices for optical communication wavelengths. (C) 1995 American Institute of Physics.
Abstract: The nonlinear-optical properties of a semi-interpenetrating polymer network of poly(vinyl alcohol) glutaraldehyde-polyaniline were studied. Large (greater than or equal to 10(-12) cm(2)/W) and fast (<50 ps) refractive optical nonlinearites were observed. The potential of this novel material for photonic applications is evaluated.
Abstract: We present experimental data and the underlying physics of spatial-phase-modulation effects associated with the thermal nonlinearity of semiconductor-doped glasses. Transient and steady-state self-focusing, laser-induced birefringence, and spatial ringing of the thermal origin were studied in this class of optical materials.
Abstract: Spatial modification of a Gaussian beam by reflection on a surface of a high-absorbing material is investigated experimentally. A theoretical description in a geometrical-optics approach is given. The usefulness and sensitivity of the method for applications in measuring laser induced surface deformation and Kerr-like nonlinear coefficients is discussed.
Abstract: Optical second-harmonic generation efficiency in Si/SixGe1-x superlattices has been compared with the corresponding values for Si(111) and Si(100). The experimentally observed increase in efficiency for structures on Si(111) can be explained by mechanical strains in superlattices and by the presence of non-centrosymmetric domains.
Abstract: The practical feasibility of designing a planar acousto-optical module for head of disk holographic memory has been studied. A planar optical system is formed from homogenous refracting waveguide lenses. The main factors that limit the density of the recorded data are identified. It is reported that a prototype of a 12-bit device was constructed and investigated.
Abstract: Methods are proposed for design calculations of the contours of homogeneous refracting waveguide lenses free of the lowest-order aberrations in a given field of view. The ray-tracing and hybrid methods of testing of lens performance are described. The optical anisotropy of lithium niobate waveguides is allowed fully in the calculations of the contours and in numerical lens testing.
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