223 research outputs found
Mathieu beams as versatile light moulds for 3D micro particle assemblies
We present tailoring of three dimensional light fields which act as light moulds for elaborate particle micro structures of variable shapes. Stereo microscopy is used for visualization of the 3D particle assemblies. The powerful method is demonstrated for the class of propagation invariant beams, where we introduce the use of Mathieu beams as light moulds with non-rotationally-symmetric structure. They offer multifarious field distributions and facilitate the creation of versatile particle structures. This general technique may find its application in micro fluidics, chemistry, biology, and medicine, to create highly efficient mixing tools, for hierarchical supramolecular organization or in 3D tissue engineering
Control of broad-area vertical-cavity surface emitting laser emission by optically induced photonic crystals
We control the emission properties of a broad-area vertical-cavity surface emitting laser by coupling it to an external feedback cavity containing a photorefractive crystal with an optically induced photonic lattice. The periodic modulation of the refractive index serves as a tunable filter and enables the dynamic suppression of unwanted spatial instabilities and modes, as originally suggested by Gomila et al
Nonlinear optics: Feature issue introduction
This joint issue of Optics Express and Optical Materials Express features 18 state-of-the art articles that witness actual developments in nonlinear optics, including those by authors who participated in the international conference Nonlinear Optics held in Waikoloa, Hawaii from July 15 to 19, 2019. As an introduction, the editors provide a summary of these articles that cover all aspects of nonlinear optics, from basic nonlinear effects and novel frequency windows to innovative nonlinear materials and devices, thereby paving the way for new nonlinear optical concepts and forthcoming applications
Extended Kramers-Moyal analysis applied to optical trapping
The Kramers-Moyal analysis is a well established approach to analyze
stochastic time series from complex systems. If the sampling interval of a
measured time series is too low, systematic errors occur in the analysis
results. These errors are labeled as finite time effects in the literature. In
the present article, we present some new insights about these effects and
discuss the limitations of a previously published method to estimate
Kramers-Moyal coefficients at the presence of finite time effects. To increase
the reliability of this method and to avoid misinterpretations, we extend it by
the computation of error estimates for estimated parameters using a Monte Carlo
error propagation technique. Finally, the extended method is applied to a data
set of an optical trapping experiment yielding estimations of the forces acting
on a Brownian particle trapped by optical tweezers. We find an increased
Markov-Einstein time scale of the order of the relaxation time of the process
which can be traced back to memory effects caused by the interaction of the
particle and the fluid. Above the Markov-Einstein time scale, the process can
be very well described by the classical overdamped Markov model for Brownian
motion.Comment: 14 pages, 18 figure
Synchronisation of spatiotemporal complex states by incoherent coupling
Synchronisation of spatiotemporal continuous disorder is realised in a Liquid Crystal Light Valve single feedback system with an incoherent, unidirectional master-slave-coupling scheme as excellent model system for synchronisation. Thus, complex states disordered in space and time were completely synchronised by using identical systems as master and slave. Thereby the impeding role of system differences is demonstrated in comparison to former experiments. A novel imaging method is introduced, in which the synchronisation process and effects like a time lag can be more easily characterised
Two-dimensional solitons with hidden and explicit vorticity in bimodal cubic-quintic media
We demonstrate that two-dimensional two-component bright solitons of an
annular shape, carrying vorticities in the components, may be
stable in media with the cubic-quintic nonlinearity, including the
\textit{hidden-vorticity} (HV) solitons of the type , whose net
vorticity is zero. Stability regions for the vortices of both types
are identified for , 2, and 3, by dint of the calculation of stability
eigenvalues, and in direct simulations. A novel feature found in the study of
the HV solitons is that their stability intervals never reach the (cutoff)
point at which the bright vortex carries over into a dark one, hence dark HV
solitons can never be stable, contrarily to the bright ones. In addition to the
well-known symmetry-breaking (\textit{external}) instability, which splits the
ring soliton into a set of fragments flying away in tangential directions, we
report two new scenarios of the development of weak instabilities specific to
the HV solitons. One features \textit{charge flipping}, with the two components
exchanging the angular momentum and periodically reversing the sign of their
spins. The composite soliton does not split in this case, therefore we identify
such instability as an \textit{intrinsic} one. Eventually, the soliton splits,
as weak radiation loss drives it across the border of the ordinary strong
(external) instability. Another scenario proceeds through separation of the
vortex cores in the two components, each individual core moving toward the
outer edge of the annular soliton. After expulsion of the cores, there remains
a zero-vorticity breather with persistent internal vibrations.Comment: 10 pages, 11 figure
Study of an Acrylamide-based Photopolymer for use as a Holographic Data Storage Medium
An acrylamide-based photopolymer formulated in the Centre for Industrial and Engineering Optics has been investigated with a view to further optimisation for holographic optical storage. Series of 15 to 30 gratings were angularly multiplexed in a volume of the photopolymer layers with different thickness at a spatial frequency of 1500 lines/mm. Since the photopolymer is a saturable material, an exposure scheduling method was used to exploit the entire dynamic range of the material and allow equal strength gratings to be recorded. From this investigation the photopolymer layer’s M/# was determined with regard to the recording geometry used. The temporal stability of photopolymer layers was studied in terms of diffraction efficiency and change of the reconstructed angle due to material shrinkage. In addition, the potential of the photopolymer as a holographic data storage medium was demonstrated by recording bit data-pages
Reduced-symmetry two-dimensional solitons in photonic lattices
We demonstrate theoretically and experimentally a novel type of localized
beams supported by the combined effects of total internal and Bragg reflection
in nonlinear two-dimensional square periodic structures. Such localized states
exhibit strong anisotropy in their mobility properties, being highly mobile in
one direction and trapped in the other, making them promising candidates for
optical routing in nonlinear lattices.Comment: 5 pages, 4 figure
Post-translational modifications soften vimentin intermediate filaments
The mechanical properties of biological cells are determined by the cytoskeleton, a composite biopolymer network consisting of microtubules, actin filaments and intermediate filaments (IFs). By differential expression of cytoskeletal proteins, modulation of the network architecture and interactions between the filaments, cell mechanics may be adapted to varying requirements on the cell. Here, we focus on the intermediate filament protein vimentin and introduce post-translational modifications as an additional, much faster mechanism for mechanical modulation. We study the impact of phosphorylation on filament mechanics by recording force-strain curves using optical traps. Partial phosphorylation softens the filaments. We show that binding of the protein 14-3-3 to phosphorylated vimentin IFs further enhances this effect and speculate that in the cell 14-3-3 may serve to preserve the softening and thereby the altered cell mechanics. We explain our observation by the additional charges introduced during phosphorylation
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