132 research outputs found
Elasticity-mediated self-organization and colloidal interactions of solid spheres with tangential anchoring in a nematic liquid crystal
Using laser tweezers and fluorescence confocal polarizing microscopy, we
study colloidal interactions of solid microspheres in the nematic bulk caused
by elastic distortions around the particles with strong tangential surface
anchoring. The particles aggregate into chains directed at about 30 degrees to
the far field director and, at higher concentrations, form complex kinetically
trapped structures. We characterize the distance and angular dependencies of
the colloidal interaction forces.Comment: 6 pages, 5 figure
Realignment-enhanced coherent anti-Stokes Raman scattering (CARS) and three-dimensional imaging in anisotropic fluids
We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to
characterize director structures in liquid crystals.Comment: 14 pages, 11 figure
CARS polarized microscopy of three-dimensional director structures in liquid crystals
We demonstrate three-dimensional vibrational imaging of director structures
in liquid crystals using coherent anti-Stokes Raman scattering (CARS) polarized
microscopy. Spatial mapping of the structures is based on sensitivity of a
polarized CARS signal to orientation of anisotropic molecules in liquid
crystals. As an example, we study structures in a smectic material and
demonstrate that single-scan CARS and two-photon fluorescence images of
molecular orientation patterns are consistent with each other and with the
structure model.Comment: 5 pages, 4 figures, published in Appl. Phys. Lett. 91, 151905 (2007
Optically induced forces and torques:Interactions between nanoparticles in a laser beam
Distinctive optical forces and torques arise between nanoparticles irradiated by intense laser radiation. These forces, associated with a pairwise process of stimulated scattering, prove to enable the possibility of producing significant modifications to both the form and magnitude of interparticle forces, with additional contributions arising in the case of dipolar materials. Moreover, such forces have the capacity to generate unusual patterns of nanoscale response, entirely controlled by the input beam characteristics- principally the optical frequency, intensity, and polarization. Based on quantum electrodynamical theory, a general result is secured for the laser-induced force under arbitrary conditions, incorporating both static and dynamic coupling mechanisms. Specific features of the results are identified for pairs of particles with prolate cylindrical symmetry, e.g., carbon nanotubes, where it is shown that the laser-induced forces and torques are sensitive functions of the pair spacing and orientation, and the laser beam geometry; significantly, they can be either repulsive or attractive according to conditions. For nanoparticles trapped in a Laguerre-Gaussian laser beam the results also reveal additional and highly distinctive torques that suggest further possibilities for nanomanipulation with light. The paper concludes with a discussion on several potential applications of such forces. © 2005 The American Physical Society
Optical vortices generated by a PANDA ring resonator for drug trapping and delivery applications
We propose a novel drug delivery system (DDS) by using a PANDA ring resonator to form, transmit and receive the microscopic volume by controlling some suitable ring parameters. The optical vortices (gradient optical field/well) can be generated and used to form the trapping tool in the same way as the optical tweezers. The microscopic volume (drug) can be trapped and moved (transported) dynamically within the wavelength router or network. In principle, the trapping force is formed by the combination between the gradient field and scattering photons, which has been reviewed. The advantage of the proposed system is that a transmitter and receiver can be formed within the same system, which is called transceiver, in which the use of such a system for microscopic volume (drug volume) trapping and transportation (delivery) can be realized
Imaging with second-harmonic radiation probes in living tissue
We demonstrate that second-harmonic radiation imaging probes are efficient biomarkers for imaging in living tissue. We show that 100 nm and 300 nm BaTiO3 nanoparticles used as contrast markers could be detected through 50 ÎĽm and 120 ÎĽm of mouse tail tissue in vitro or in vivo. Experimental results and Monte-Carlo simulations are in good agreement
Three dimensional optical manipulation and structural imaging of soft materials by use of laser tweezers and multimodal nonlinear microscopy
We develop an integrated system of holographic optical trapping and
multimodal nonlinear microscopy and perform simultaneous three-dimensional
optical manipulation and non-invasive structural imaging of composite
soft-matter systems. We combine different nonlinear microscopy techniques such
as coherent anti-Stokes Raman scattering, multi-photon excitation fluorescence
and multi-harmonic generation, and use them for visualization of long-range
molecular order in soft materials by means of their polarized excitation and
detection. The combined system enables us to accomplish both, manipulation in
composite soft materials such as colloidal inclusions in liquid crystals as
well as imaging of each separate constituents of the composite material in
different nonlinear optical modalities. We also demonstrate optical generation
and control of topological defects and simultaneous reconstruction of their
three-dimensional long-range molecular orientational patterns from the
nonlinear optical images
Second-harmonic generation from coupled plasmon modes in a single dimer of gold nanospheres
We show that a dimer made of two gold nanospheres exhibits a remarkable
efficiency for second-harmonic generation under femtosecond optical excitation.
The detectable nonlinear emission for the given particle size and excitation
wavelength arises when the two nanoparticles are as close as possible to
contact, as in situ controlled and measured using the tip of an atomic force
microscope. The excitation wavelength dependence of the second-harmonic signal
supports a coupled plasmon resonance origin with radiation from the dimer gap.
This nanometer-size light source might be used for high-resolution near-field
optical microscopy.Comment: 6 pages, 5 figure
Mode-matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation
Boosting nonlinear frequency conversion in extremely confined volumes remains
a key challenge in nano-optics, nanomedicine, photocatalysis, and
background-free biosensing. To this aim, field enhancements in plasmonic
nanostructures are often exploited to effectively compensate for the lack of
phase-matching at the nanoscale. Second harmonic generation (SHG) is, however,
strongly quenched by the high degree of symmetry in plasmonic materials at the
atomic scale and in nanoantenna designs. Here, we devise a plasmonic
nanoantenna lacking axial symmetry, which exhibits spatial and frequency mode
overlap at both the excitation and the SHG wavelengths. The effective
combination of these features in a single device allows obtaining unprecedented
SHG conversion efficiency. Our results shed new light on the optimization of
SHG at the nanoscale, paving the way to new classes of nanoscale coherent light
sources and molecular sensing devices based on nonlinear plasmonic platforms.Comment: 14 pages, 4 figure
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