Optical Induction Research Articles

Electromagnetically induced transparency in vacuum and buffer gas potassium cells probed via electro-optic frequency combs.

Electromagnetically induced transparency (EIT) in K39 and K41 was probed using electro-optic frequency combs generated by applying chirped waveforms to a phase modulator. The carrier tone of the frequency comb served as the pump beam and induced the necessary optical cycling. Comb tooth spacings as narrow as 20kHz were used to probe potassium in both buffer gas and evacuated cells at elevated temperatures. Atomic absorption features as narrow as 33(5)kHz were observed, allowing for the K39 lower-state hyperfine splitting to be optically measured with a fit uncertainty of 2kHz. Due to the ultranarrow width of the EIT features, long-lived optical free induction decays were also observed which allowed for background-free detection.

Compact flat band states in optically induced flatland photonic lattices

We realize low-dimensional tight-binding lattices that host flat bands in their dispersion relation and demonstrate the existence of optical compact flat band states. The lattices are resembled by arrays of optical waveguides fabricated by the state-of-the-art spatio-temporal Bessel beam multiplexing optical induction in photorefractive media. We work out the decisive details of the transition from the discrete theory to the real optical system ensuring that the experimental lattices stand up to numerical scrutiny exhibiting well-approximated band structures. Our highly flexible system is a promising candidate for further experimental investigation of theoretically studied disorder effects in flat band lattices.

Effects of mechanical processing and annealing on optical coherence properties of [formula omitted]:LiNbO3 powders

Optical coherence lifetimes and decoherence processes in erbium-doped lithium niobate (Er3+:LiNbO3) crystalline powders are investigated for materials that underwent different mechanical and thermal treatments. Several complimentary methods are used to assess the coherence lifetimes for these highly scattering media. Direct intensity or heterodyne detection of two-pulse photon echo techniques was employed for samples with longer coherence lifetimes and larger signal strengths, while time-delayed optical free induction decays were found to work well for shorter coherence lifetimes and weaker signal strengths. Spectral hole burning techniques were also used to characterize samples with very rapid dephasing processes. The results on powders are compared to the properties of a bulk crystal, with observed differences explained by the random orientation of the particles in the powders combined with new decoherence mechanisms introduced by the powder fabrication. Modeling of the coherence decay shows that paramagnetic materials such as Er3+:LiNbO3 that have highly anisotropic interactions with an applied magnetic field can still exhibit long coherence lifetimes and relatively simple decay shapes even for a powder of randomly oriented particles. We find that coherence properties degrade rapidly from mechanical treatment when grinding powders from bulk samples, leading to the appearance of amorphous-like behavior and a broadening of up to three orders of magnitude for the homogeneous linewidth even when low-energy grinding methods are employed. Annealing at high temperatures can improve the properties in some samples, with homogeneous linewidths reduced to less than 10kHz, approaching the bulk crystal linewidth of 3kHz under the same experimental conditions.

Direct access to the optically active VAChT inhibitor vesamicol and its analogues via the asymmetric aminolysis of meso-epoxides with secondary aliphatic amines.

First highly enantioselective synthesis of biologically important vesamicol, benzovesamicol, and their derivatives was achieved via the desymmetrization of meso-epoxides with secondary aliphatic amines (4-phenylpiperidine derivatives) using a chiral [salenCo(iii)-BF4] catalyst at room temperature. All products were obtained in good yield and with excellent optical induction.

The Effect of Alignment Changes on Unilateral Transtibial Amputee's Gait: A Systematic Review.

IntroductionProsthetic alignment, positioning of a prosthetic foot relative to a socket, is an iterative process in which an amputee’s gait is optimized through repetitive optical gait observation and induction of alignment adjustments when deviations are detected in spatiotemporal and kinematic gait parameters. An important limitation of the current prosthetic alignment approach is the subjectivity and the lack of standardized quantifiable baseline values. The purpose of this systematic review is to investigate if an optimal alignment criterion can be derived from published articles. Moreover, we investigated the effect of alignment changes on spatiotemporal, kinematic and kinetic gait parameters.ResultsA total of 11 studies were included, two controlled before-and-after studies and nine-interrupted time series studies.DiscussionThe results demonstrate that alignment changes have a predictable influence on the included kinetic parameters. However, the effect of alignment changes on spatio-temporal and kinematic gait parameters are generally unpredictable. These findings suggest that it is imperative to include kinetics in the process of dynamic prosthetic alignment. Partially this can be established by communication with the prosthetic user in terms of perceived socket comfort, but the use of measurement tools should also be considered. While current literature is not conclusive about an optimal alignment, future alignment research should focus on alignment optimisation based on kinetic outcomes.

Tunable CO2 laser system with subnanosecond-pulse-train output

A CO2 laser system has been demonstrated that generates a train of subnanosecond pulses tunable over the P and R branches of the CO2 laser spectrum at 9–11µm. It utilizes optical free induction decay to generate a single ~100-ps laser pulse from a tunable transverse-excited-atmospheric CO2 laser. This laser pulse is injection-seeded into a high-pressure CO2 oscillator whose output consists of a train of amplified ~100-ps pulses with maximum pulse energy of 30mJ, corresponding to a peak power of 300MW. The ~100-ps, tunable, infrared laser pulses are needed for a new technique to remotely detect atmospheric gaseous molecules, which relies on the train of CO2 laser pulses selectively exciting the target molecules whose presence is then revealed using a separate terahertz probe beam.

Observation of spatially oscillating solitons in photonic lattices

We report on the experimental observation of spatially oscillating solitons in two-dimensional nonlinear photonic lattices, realized by optical induction using a continuous nondiffracting Weber beam. Thereby, we introduce and demonstrate a new type of transverse soliton dynamics originating from the unique parabolic geometry of the photonic lattice. First, we numerically calculate the fundamental soliton solution for this lattice and experimentally demonstrate its existence. Afterwards, we experimentally launch the soliton with an additional transverse momentum and observe harmonic spatial oscillation during propagation.

Light-induced gene expression with photocaged IPTG for induction profiling in a high-throughput screening system.

BackgroundInducible expression systems are frequently used for the production of heterologous proteins. Achieving maximum product concentrations requires induction profiling, namely the optimization of induction time and inducer concentration. However, the respective experiments can be very laborious and time-consuming. In this work, a new approach for induction profiling is presented where induction in a microtiter plate based cultivation system (BioLector) is achieved by light using photocaged isopropyl β-d-1-thiogalactopyranoside (cIPTG).ResultsA flavin mononucleotide-based fluorescent reporter protein (FbFP) was expressed using a T7-RNA-polymerase dependent E. coli expression system which required IPTG as inducer. High power UV-A irradiation was directed into a microtiter plate by light-emitting diodes placed above each well of a 48-well plate. Upon UV irradiation, IPTG is released (uncaged) and induces product formation. IPTG uncaging, formation of the fluorescent reporter protein and biomass growth were monitored simultaneously in up to four 48-well microtiter plates in parallel with an in-house constructed BioLector screening system. The amount of released IPTG can be gradually and individually controlled for each well by duration of UV-A exposure, irradiance and concentration of photocaged IPTG added at the start of the cultivation. A comparison of experiments with either optical or conventional IPTG induction shows that product formation and growth are equivalent. Detailed induction profiles revealed that for the strain and conditions used maximum product formation is reached for very early induction times and with just 6–8 s of UV-A irradiation or 60–80 µM IPTG.ConclusionsOptical induction and online monitoring were successfully combined in a high-throughput screening system and the effect of optical induction with photocaged IPTG was shown to be equivalent to conventional induction with IPTG. In contrast to conventional induction, optical induction is less costly to parallelize, easy to automate, non-invasive and without risk of contamination. Therefore, light-induced gene expression with photocaged IPTG is a highly advantageous method for the efficient optimization of heterologous protein production and has the potential to replace conventional induction with IPTG.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0461-3) contains supplementary material, which is available to authorized users.

Optical Magnetic Induction Tomography of the Heart.

Atrial Fibrillation (AF) affects a significant fraction of the ageing population, causing a high level of morbidity and mortality. Despite its significance, the causes of AF are still not uniquely identified. This, combined with the lack of precise diagnostic and guiding tools, makes the clinical treatment of AF sub-optimal. We identify magnetic induction tomography as the most promising technique for the investigation of the causes of fibrillation and for its clinical practice. We therefore propose a novel optical instrument based on optical atomic magnetometers, fulfilling the requirements for diagnostic mapping of the heart’s conductivity. The feasibility of the device is here discussed in view of the final application. Thanks to the potential of atomic magnetometers for miniaturisation and extreme sensitivity at room temperature, a new generation of compact and non-invasive diagnostic instrumentation, with both bedside and intra-operative operation capability, is envisioned. Possible scenarios both in clinical practice and biomedical research are then discussed. The flexibility of the system makes it promising also for application in other fields, such as neurology and oncology.

Demonstration of flat-band image transmission in optically induced Lieb photonic lattices.

We present a simple, yet effective, approach for optical induction of Lieb photonic lattices, which typically rely on the femtosecond laser writing technique. Such lattices are established by judiciously overlapping two sublattices (an "egg-crate" lattice and a square lattice) with different periodicities through a self-defocusing photorefractive medium. Furthermore, taking advantage of the superposition of localized flat-band states inherent in the Lieb lattices, we demonstrate distortion-free image transmission in such two-dimensional perovskite-like photonic structures. Our experimental observations find good agreement with numerical simulations.

Optical vortex induction via light–matter interaction in liquid-crystal media

Optical vortices are attracting much attention because of their applications in various fields of optical processing, communications, enhanced imaging systems, and bio-inspired devices. Different methods to generate optical vortices have been devised to date. Among them, several are based on the exploitation of light–matter interaction in liquid-crystal media. This review focuses on the main mechanisms of vortex generation in liquid crystals, in particular on vortex generation induced by umbilics, that is, defects arising in homeotropically aligned nematic cells, which act as topological matter templates able to realize the conversion from spin to orbital angular momentum of an incoming Gaussian beam. Optical vortex induction in a photosensitive light valve is presented as a self-stabilizing mechanism leading to reconfigurable and programmable vortex arrays. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler, converting input arrays of circularly polarized beams into output arrays of vortex beams with topological charges consistent with the matter lattice symmetry.

Soliton formation by decelerating interacting Airy beams.

We demonstrate a new type of soliton formation arising from the interaction of multiple two-dimensional Airy beams in a nonlinear medium. While in linear regime, interference effects of two or four spatially displaced Airy beams lead to accelerated intensity structures that can be used for optical induction of novel light guiding refractive index structures, the nonlinear cross-interaction between the Airy beams decelerates their bending and enables the formation of straight propagating solitary states. Our experimental results represent an intriguing combination of two fundamental effects, accelerated optical beams and nonlinearity, together enable novel mechanisms of soliton formation that will find applications in all-optical light localization and switching architectures. Our experimental results are supported by corresponding numerical simulations.

Over-expression and Purification of Recombinant 3C-like Protease from Black Queen Cell Virus in Escherichia coli

Black queen cell virus is one of the members belonging to Picornavirus, which possesses a 3C-like protease. Viral replication and capsid assembly in the order Picornavirales require polyprotein proteolysis processing, which is performed by 3C or 3C-like (3CL) proteases. Therefore, viral proteases are attractive targets for anti-viral therapy. The complete 3C-like protease gene from Black queen cell virus was cloned into pGEM-3Zf(+) vector, and the amino acid sequence revealed a high homology (99.1%) to 3C-like protease deposited in a reference Genbank EF517515.1. For the expression, 3C-like protease gene was subcloned into pMAL-C2 vector system. The expression level of MBP-BQCV-3CL protein was evaluated under different standards of cell optical density, IPTG concentration, induction time, and induction temperature. As the result, the optimal condition was confirmed as the induction with 0.1mM IPTG at 25°C for 6 hours, and a purification step using amylose resin reached a high protein yield of approximately 2.22mg per 1ml of cultured cells. Purified MBP-BQCV-3CL proteins can provide an important antigen source to generate monoclonal antibody and will become a potential candidate for anti-viral drugs, which can inactivate 3C-like protease function as well as BQCV replication.

Picosecond laser surface micropatterning of ceramics by optical fiber induction

Parallel microgrooves and mesh structure with a line width of about 16 μm, which is much smaller than the diameter of the laser focus spot of 50 μm, are fabricated on Al2O3 ceramic surfaces by picosecond laser patterning with optical fiber induction. The patterned grooves are of high quality without burr, recasting or thermally induced cracks. Grain refinement of the groove surfaces caused by the rapid condensation and redeposition during picosecond laser irradiation with optical fiber induction improved the smoothness and mechanical strength of the grooves. Different patterns can be fabricated by adjusting the optical fiber layout, which is independent of the laser scanning direction. The regions etched by the laser are kept in near-field contact with the optical fibers when the laser beam passes through the fibers and irradiates the ceramic surface. This results in localized field enhancement between the transparent optic fiber and ceramic surface, which produces the precise microgrooves. The developed technique allows high-resolution micromachining of the surfaces of hard and brittle ceramic-type materials.

Optical induction of non-diffracting discrete photonic lattice

The triangle lattices was optically induced in an externally biased cerium doped strontium barium niobate (SBN) photorefractive crystal using a mask with three holes or six holes, respectively. Numerically, the transmittance function of the amplitude mask and its Fourier-transform function were given out instead of treating each hole as a simple point source. Experimentally, the differences between the two lattices were analyze by phase distribution, far-field diffraction pattern, Brillouin-zone spectroscopy. And the three-dimensional (3D) images by computer simulation are also used to study their differences. In addition, the anisotropy lattices are presented by designing the amplitude mask properly.

Artificial Graphene and Related Photonic Lattices Generated With a Simple Method

We fabricate honeycomb and related photonic lattices in a nonlinear crystal with a simple method that is based on the optical Fourier transformation through an amplitude mask (six-hole aperture) superimposed with a phase mask (three tilted glass plates). Compared with using the spatial light modulator, our method is cost-effective and easy to control for almost every one. Numerically, we use the transmittance function to describe the amplitude mask instead of treating each hole as a simple point source and give out the field distribution function of the honeycomb lattice beam. Experimentally, the induced lattice structure is examined by the Brillouin zone spectroscopy and the far-field diffraction pattern, as well as by monitoring the linear and nonlinear propagation of a probe beam. In addition to the honeycomb, vortex, and Kagome lattices, we illustrate the phase conditions for optical induction of molybdenum disulfide-like photonic lattices for the first time. Our approach can be easily extended to generate more complex microstructures by designing the amplitude and phase mask properly, promising a convenient way to establish a photonic platform for various applications.

Optical induction of Bessel-like lattices in methyl-red doped liquid crystal cells

The optical induction of annular photonic lattices by a traveling Bessel beam has been investigated in Methyl-red (MR) doped nematic liquid crystal (LC). Non-diffracting Bessel beams were formed by an axicon. The induced Bessel-like lattice had a ~15µm period in the radial direction. The lattice was tested by measuring the forward diffracted power of the recording Bessel beam. The dependency on the angle between the polarization of the laser beam and the director of the LC and on the axial position of the LC cell had been investigated. A diffraction efficiency of 14% had been obtained. Investigations have been performed for different MR dye doping concentrations. An erasure time of the lattice of 60s has been determined by a 532nm probe Gaussian beam of 2mW in a LC cell with MR dye concentration of 1.15 wt%. The induced periodically varying refractive index in the LC medium is analogous to microstructured fibers and allows the study of light localization and soliton behavior in highly nonlinear waveguide arrays.

Polymerization of Norbornene Using Chiral Bis(phenolate) Zirconium Catalysts

Norbornene is polymerized by employing zirconium catalysts with (OSSO)-type bis(phenolate) ligands. The racemic precatalyst rac-1 produces high molecular weight poly(norbornene) with slight optical activity. Enantiopure precatalysts (S,S)-1 and (R,R)-1 are used to study the optical induction in the poly(norbornene)s formed. To overcome the insolubility of poly(norbornene)s in common solvents, their microstructure is studied using copolymers with ethylene as well as hydrooligomers. The crystal structure of a norbornene tetramer is reported.

Optical induction scheme for assembling nondiffracting aperiodic Vogel spirals

We introduce an experimental approach to realize aperiodic photonic lattices based on multiplexing of nondiffracting Bessel beams. This holographic optical induction scheme takes advantage of the well localized Bessel beam as a basis to assemble two-dimensional photonic lattices. We present the realization of an optically induced two-dimensional golden-angle Vogel spiral lattice, which belongs to the family of deterministic aperiodic structures. With our technique, a very broad class of photonic refractive index landscapes now becomes accessible to optical induction, which could not be realized with established distributed holographic techniques.

Propagation dynamic of a Gaussian in the inverted nonlinear photonic crystals

In this work, we study the evolution of a Gaussian beam inside a one-dimensional inverted nonlinear photonic crystals (INPC) with a Kerr nonlinearity. The INPC is a kind of virtual crystals which is generated by the optical induction via the electromagnetically induced transparency (EIT). The propagation dynamics of the Gaussian with different total power are identified. Four types of propagation behavior are found. They are collapse beam, breather beam, soliton and symmetry-breaking beam, respectively. The border between these four behavior types are given. For symmetry-breaking beam, an asymmetric profile of the beam is evolving from the symmetry Gaussian, which can be termed as a kind of dynamical symmetry breaking (DSB). The influences on the appearance of the symmetry breaking point are studied by varying input parameters of the Gaussian. The results of this work are both suitable in nonlinear optics and Bose-Einstein condensate (BEC).