This PDF file contains the front matter associated with SPIE Proceedings Volume 6483, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Light induced binding energy between particles in the Rayleigh range in laser fields varies as 1/r. This long range dependence suggests a diverging increase of the binding force when the number of interacting particles becomes large. Theoretical studies performed for 1D periodic chains of dipoles reveals large binding field enhancement for an optimum number of interacting particles. When the number of dipoles overshoots this number, the binding intensity collapses. This result is consistent with experimental observations of periodicity defects in large 2D optically built crystals. Some solutions are explored to keep large binding field enhancement for large crystals. Shrinking the coherence length and phase modulating the incident trapping light are among the proposed schemes.

Two mirrors guiding light experience attractive or repulsive forces according to the eigenmode type of symmetry, but regardless of the specific details of the guiding structure. A transverse evanescent mode (TM or TE) that has an anti-symmetric transverse field causes repulsion, while attraction occurs when the mode has a symmetric transverse field. Transverse propagating modes, however, are always repulsive. One possible application for this phenomenon is to use a symmetric mode supported, for instance, by two properly designed Bragg mirrors. By varying the wavelength of the mode injected into the waveguide, it is possible to cross the light-line and switch between attraction and repulsion. If the mirror is free to move in the transverse direction, then this is a scheme for controlling its motion. Another possibility is to create a stable equilibrium with a superposition of transverse evanescent symmetric and anti-symmetric modes. For this purpose, a more appealing configuration than Bragg mirrors is a waveguide that consists of two dielectric slabs where the light is guided by total internal reflection. Each slab is trapped in a potential well resulting in optical binding by eigenmodes.

It is well known that the forces which light imparts on micro- and nanoparticles arise due to intensity gradients and dielectric mismatch. For laser-irradiated atoms and molecules, optical forces primarily result from close resonance between the optical frequency and an electronic transition. Recently it has emerged that optically induced pair forces also arise, through a modification of Casimir-Polder interactions; preliminary assessments of the mechanism have largely centered on nanoparticle systems. In this paper, we show that a potentially very significant effect can be anticipated in the condensed phase, an optically induced modification of interatomic forces that is capable of generating anisotropic patterns of laser-induced compression and expansion. This phenomenon, termed optical electrostriction, should be measurable and significant when high intensity laser light is transmitted through even an essentially nonabsorptive material. However, the full conditions for observation of the effect are such that some competing interactions might also arise. Key parameters that determine the size and character of optical electrostriction are delineated and possible applications are considered, including optical actuators for nanoscale electromechanical systems.

We demonstrate an experimental technique for manipulating atom clouds with high-speed and high resolution. By combining holographically engineered laser beams from a spatial light modulator with acousto-optic deflection, we manipulate the spatial locations of multiple cold atom clouds held in dark optical traps with individual site control. Additionally, we demonstrate smooth 2-dimensional motion of atomic ensembles.

In this proceeding we present ongoing projects concerning high resolution measurements developed for future space missions based on ultracold atoms at the Institut fur Quantenoptik (IQ) of the Leibniz-Universitat Hannover. This work involves the realization of a Bose Einstein condensate in microgravitational environment and an inertial atomic quantum sensor.

We demonstrate the generation of single-beam dark toroidal optical intensity distributions, which are of interest for neutral atom storage and atom interferometry. We demonstrate experimentally and numerically optical potentials that contain a ring-shaped intensity minimum, bounded in all directions by higher intensity. We use a spatial light modulator to alter the phase of an incident laser beam, and analyze the resulting optical propagation characteristics. For small toroidal traps (< 50 &mgr;m diameter), we find an optimal superposition of Laguerre-Gaussian modes that allows the formation of single-beam toroidal traps. We generate larger toroidal bottle traps by focusing hollow beams with toroidal lenses imprinted onto the spatial light modulator.

Although disorder plays a crucial role in many systems, it can usually not be chosen or controlled. We show that the unique methods available for ultracold atomic gases may be used for the controllable production and observation of disordered quantum systems. A detailed analysis of localization effects for two possible realizations of a disordered potential is presented. In a theoretical analysis clear localization effects are observed when a superlattice is used to provide a quasiperiodic disorder. The effects of localization are analyzed by investigating the superfluid fraction and the localization length within the system.

One very important contribution of the Optical Tweezers technique is its ability to extract the missing mechanical measurements in the world of microorganisms and cells that could be correlated to biochemical information. A microsphere displacement is the preferential force transducer for this kind of measurement. However, the typical conditions used in Optical Tweezers with very high numerical aperture beams and microspheres with diameters up to ten wavelengths, requires a full vectorial description of the incident beam in partial waves with the origin of coordinate system at the center of the microsphere and not at the focus of the beam. Using the Angular Spectrum Representation of the incident beam and an analytical expression for integrals involving associated Legendre Polynomials, Bessel functions and plane waves we have been able to obtain a closed expression, without any approximation, for the beam shape coefficients of any orthogonally incident beam. The theoretical prediction of the theory agrees well with the experimental results performed on a 3D positioned dual trap in an upright standard optical microscope, thus obtaining the whole optical force curves as a function of the microsphere center for different wavelengths.

We present a multiple laser tweezers system based on refractive optics. The system produces an array of 100 optical traps thanks to a refractive microlens array, whose focal plane is imaged into the focal plane of a high-NA microscope objective. This refractive multi-tweezers system is combined to micro-fluidics, aiming at performing simultaneous biochemical reactions on ensembles of free floating objects. Micro-fluidics allows both transporting the particles to the trapping area, and conveying biochemical reagents to the trapped particles. Parallel trapping in micro-fluidics is achieved with polystyrene beads as well as with native vesicles produced from mammalian cells. The traps can hold objects against fluid flows exceeding 100 micrometers per second. Parallel fluorescence excitation and detection on the ensemble of trapped particles is also demonstrated. Additionally, the system is capable of selectively and individually releasing particles from the tweezers array using a complementary steerable laser beam. Strategies for high-yield particle capture and individual particle release in a micro-fluidic environment are discussed. A comparison with diffractive optical tweezers enhances the pros and cons of refractive systems.

The development of new photonic and plasmonic devices rely on the new pioneering techniques of micro- and nanofabrication, combining both standard lithography techniques and self-assembly. The combination of colloidal crystals, projection patterning and soft-lithography are examples of fabrication techniques which allow to obtain complex structures of sizes smaller than the wavelength of visible light. In many cases, the structures fabricated by this way are not possible to obtain using standard lithography techniques, like electron-beam, UV-VIS lithography and focused ion beam (FIB). We have used two-dimensional colloidal crystals as templates to fabricate arrays of isolated metallic particles of triangular shape on surfaces and two-dimensional gratings. Either dielectric or metallic structures can be obtained. In the later case the coupling between light and the locally confined surface plasmon-polaritons leads to resonances, field enhancements and other related phenomena. The scattering properties of the particles and gratings have been investigated experimentally, using a confocal, a near- field optical microscope and a spectrometer, and theoretically, using FDTD methods. We show that triangular particles of noble metals are highly sensitive to the relative direction of incidence of light and its polarization. On the other hand, the light scattered in the direction perpendicular to the plane of the particles reveals strong spectral dependency. This dependency can be exploited to fabricate photonics devices sensitive to the direction of incidence of light.

Evanescent Wave (EW) fluorescence spectroscopic techniques are exploited to obtain information about the conformational state of macromolecules within close proximity of a solid/liquid interfacial region. Specifically, timeresolved evanescent wave-induced fluorescence techniques have been applied to the study of the adsorption of polymers and biomolecules to silica surfaces. We have extended these EW measurements using polarized excitation and emission detection to probe molecular motion and conformational change in the microenvironment of the interfacial region. We report on the observation of complex time-dependent fluorescence anisotropy data and the interpretation of these data in terms of in- and out-of-plane rotational motion. The macromolecular-interfacial systems investigated by this evanescent wave approach included polymer film dynamics and adsorbed protein rearrangement upon adsorption.

Holographic optical trapping uses forces exerted by computer-generated holograms to organize microscopic materials into three-dimensional structures. Achieving and verifying accurate three-dimensional placement requires methods for assessing the accuracy of the projected traps' geometry, as well as methods for measuring trapped objects' three-dimensional positions. Volumetric imaging of the projected trapping pattern solves one problem. Holographic video microscopy addresses the other. The combination is exceptionally effective for organizing, inspecting and analyzing soft-matter systems.

Kawata and Tani's [4] experiments showed that the evanescent field created on the surface of an ion exchanged waveguide could trap and move microparticles. This opened up the possibility of combining conventional optical trapping with integrated optics in order to create new microsystems for the manipulation of particles or biological objects. Recently, the use of strip silicon nitride waveguides increased the performances of these systems enabling higher particles speeds and reduced guided power [12]. Our experiments demonstrate that polarization affects drastically the way particles are propelled along the waveguide surface. For example in TM polarization, 0,6 &mgr;m diameter gold particles are moving along the center of the waveguide whereas in TE, they are propelled along its sides. Moreover, it appears that gradient forces involved in this phenomenon depend on the particle size. To understand this behavior, a numerical approach of the problem based on the finite element method has been developed. This method enables the calculation of the 3D distribution of the electric fields. The resulting optical forces are calculated thanks to the Maxwell stress tensor formalism. This first experimental and theoretical illustration of repulsive gradient forces on metallic particles opens up perspectives for polarization based sorting systems.

We describe a class of diffractive optical elements that intended for use in holographic optical trapping systems to project ring-like optical traps. The ring traps' hologram is design by shape-phase algorithm, that incodes amplitude information in Fourier space into shape. The flexibility of the shape-phase algorithm leeds to several advantages over commonly used optical vorteces. While, optical vorteces carry orbital angular momentum which determines the vortex diameter, ring trap dimensions do not depend on the angular momentum. In particular, we formed a ring trap without angular momentum, or tangetial-force. Also unlike most optical vortices or ring-like Bessel beams, these ring traps have strong enough axial intensity gradients to trap objects in three dimensions. We investigated the three dimensional vortex-like trapping experimentaly and by volumetric imaging.

Non linear propagation of ultra short pulses in air is studied. By preparing an initial field distribution by an amplitude mask we can obtain a Townes soliton[1] (self similar channel of coherent radiation) in air. Experimental observation can be described accurately by the numerical integration of the Non Linear Schroedinger Equation (NLSE) and allow us to explain the origin of the remarkable stability of this soliton as a balance between diffraction and Kerr effect. We further explore on the role of coherence by revisiting the two slit Young's experiment but now in the non linear regime.

Spatial Light Modulators (SLMs) have been successfully used for beam sculpting in the area of optical manipulation, however in some applications their associated pixelation, slow switching speeds, and incident power limitations can be undesirable. An alternative device that overcomes these problems is the Tunable Acoustic Gradient index (TAG) lens. This device uses acoustically induced density and refractive index variations within a fluid to spatially phase modulate a transmitted laser beam. The acoustic waves within the fluid are generated via a piezoelectric transducer. When driven with a frequency-modulated signal, arbitrary optical phase modulation patterns can be generated at regular time intervals. The resulting sculpted beam is best observed using a pulsed laser synchronized to the frequency-modulated signal of the TAG lens. As this device is purely analog, there is no pixelation in the phase modulation pattern. Also, because the only major requirement on the fluid is that it be transparent, it is possible to select fluids with high damage thresholds and high viscosities. High damage thresholds allow the TAG lens to be used in high power applications that would be unsuitable for an SLM. High viscosities provide fast damping of transient density variations and increase switching speeds between patterns. Discussion here will be limited to axially symmetric beam sculpting, however the results can be generalized to asymmetric cases.

The modes in an optical cavity between two astigmatic mirrors have a twisted structure when the mirror axes are not aligned. We use operator techniques to obtain a full characterization of these modes. The method is exact in the paraxial limit. The structure of the modes is completely determined by the geometry of the resonator. This geometry is given by the separation between the mirrors, their radii of curvature, and the relative orientation of their symmetry axes. The fundamental mode has elliptical Gaussian intensity profiles and the intersections of a nodal plane with a transverse plane normal to the axis can be ellipses or hyperbolae. The symmetry axes of the intensity curves and the nodal curves are not aligned. At the mirrors, the higher-order modes have a Hermite-Gaussian structure. Their analytical form can be generated from the fundamental mode by using raising operators that generalize the operators that are known in the description of the quantum harmonic oscillator. In the interior region of the resonator, admixture of Laguerre-Gaussian structures can arise, resulting in vortices.

Recently, spatial light modulators (SLMs) have been used to generate polarization-engineered laser beams, such as radially polarized doughnut modes, which may provide advantages for excitation of fluorophore dipoles in single-molecule (SM) spectroscopy. Here we investigate the additional use of SLMs for spatially-dependent transformation of the collected fluorescence field with a goal to improve the fidelity of three-dimensional molecular orientation determination. Numerical calculations of a high numerical aperture single-molecule confocal microscope are presented in which a SLM is placed in the back focal plane of the objective. The coherently imaged fluorescence undergoes spatially-dependent phase and polarization transformation by the SLM, before it passes to a polarization beamsplitter, and is subsequently focused onto two pinholes and single-photon avalanche photodiodes. We calculate the electric vector field in the back focal plane of the objective using the Weyl representation and taking into account the forbidden light emitted at angles above the critical angle of the cover glass-immersion fluid interface. The calculated electric field is then subject to the spatially-dependent polarization change implemented by SLM. We numerically study the effects of polarization control on the microscope sensitivity to molecule orientation. We also analyze the combined use of the intensity and polarization information in the back focal plane of the SM microscope for single-molecule orientation determination.

We present our current efforts to create pure transversal modes in ultrashort and intense pulses of 800 nm radiation (Ti:sapphire). Our longer-term goal is to investigate if and how optical orbital angular momentum affects intense-field excitation and ionization processes. For this purpose we need strong pulses in pure modes. Optical orbital angular momentum is present in Laguerre-Gaussian modes; in the past, we established a technique to create spatial-chirp free pure Laguerre-Gaussian modes using a pair of holographic gratings on film [Opt. Express 13, 7599-7608 (2005)]. However, this technique is unsuitable for high intensity beams, and we are currently exploring the possibilities of a liquid-crystal spatial light modulator (SLM). After careful testing, we have found that our SLM, which we operate as a phase plate, withstands without any problem the full 10¹⁰ W/cm² peak intensity of an amplified pulsed Ti:sapphire beam (< 50 fs pulse duration, repetition rate 1 kHz). Using the SLM, we have recently created a beam of ultrashort and intense pulses with a Hermite-Gaussian(1,0) profile and started to analyze this beam using optical and ionization methods.

The interaction between light and particles in an optical trap provides a tool for physicists to study Brownian motion and dynamics for objects in the micron to nano-sized regime. In this paper, we describe how the forward scattering light field from micro-particles trapped in an optical vortex beam provides a means of studying the helicity and coherence of the trapping beam. Hence, optical trapping may be implemented to study of the relative phase and spatial coherence of two points in trapping light fields with arbitrary wavefronts.

Helico-conical optical beams are a recently introduced class of beams that multiplicatively combine helical and conical phase fronts. Focusing these beams leads to a spiral intensity distribution at the focal plane of the lens. Further theoretical and experimental examination reveals interesting three-dimensional intensity patterns near the focal region, including a cork-screw structure around the optical axis. Variations on these light distributions based on the superposition of multiple helico-conical beams are also presented here. These beams are expected to yield interesting dynamics when applied to the optical trapping of microscopic particles, such as dielectric microspheres or even biological cells.

We show the first coherent white-light optical vortices generated from supercontinuum that have the azimuthally varying phase structure consistent with a monochromatic Laguerre-Gaussian beam and zero angular dispersion. Two methods of Laguerre-Gaussian supercontinuum generation are discussed and contrasted. We use a computer generated hologram to convert a Gaussian white-light supercontinuum source into Laguerre-Gaussian supercontinuum.

Colloidal particles driven by an optical vortex constitute a model driven-dissipative system in which both macroscopic and microscopic aspects of transport can be studied. We find that the single-particle diffusion in an optical vortex can be either normal super-diffusive or sub-diffusive depending on the number of particles in the vortex and on the timescale over which the diffusion is measured. For a three particle system we find that the particles dynamics can be either steady-state periodic or with weakly chaotic characteristics depending on the relative efect of modulations in the intensity along the vortex and hydrodynamic interactions between the spheres. We introduce the use of the N-fold bond orientational order parameter to characterize particle circulating in a ring by one macroscopic quantity. for a three particle system we show that for short time scales the single-particle super-diffusion corresponds to a super-diffusive motion of the order parameter. At longer time scales we find that the order parameter asymptotes to the expected normal di.usion behavior for the steady state system, while fractional dynamics develop in the weakly chaotic system. Moreover, we confirm a prediction that related the power laws governing the fractional dynamics with those governing the weakly chaotic behavior.

We study the optical fields produced by non-integral binary forked gratings. We analyze experimentally the phase structure of the light beams by interference. We were able to identify individual optical vortices directly by observing the dislocations in the fringe pattern. Our experimental results agree well with of all the generic features predicted by the theoretical model [M.V. Berry, "Optical vortices evolving from helicoidal and fractional phase steps," J. Opt. A 6, pp. 259-268, 2004.]. Our results underscore the conservation of orbital angular momentum of the light/optical-apparatus system.