Optical Fourier Research Articles

Nanoapertures with ordered rotations: symmetry transformation and wide-angle flat lensing.

We report the experimental demonstration of a two-dimensional (2D) metasurface with ordered rotation of elements and show that it can be used to control the symmetry of light-matter interaction. A 2D lens is demonstrated in the visible region by transforming the rotational symmetry associated with the off-axis incident light to the translational symmetry, allowing an extraordinarily large field of view (FOV) as well as optical Fourier transformation. Furthermore, such a planar lens has a long focal depth, with polarization selectivity and subwavelength resolution. The scheme presented here may provide many new perspectives on the design of novel 2D optical devices.

Optical Image Self-Convolution Based on Second-Harmonic Generation With a Single Spatial Light Modulator

By combining optical Fourier transform with second-harmonic generation (SHG) from infrared to visible region in a periodically poled Magnesium-doped Lithium Niobate (PPLN) crystal, we present a simple yet efficient experiment to revisit the optical implementation of image self-convolution. In contrast to previous scheme, here the main feature is the holographic gratings we prepare by a phase-only spatial light modulator that enables a deeper understanding on the centrosymmetry for intensity images, and particularly, the conjugate symmetry for both intensity and phase images. We manifest both cases by observing the real-time autocorrelation peaks that appear gradually in the output SHG signals. As our optical scheme possesses the inherent capacity of parallel processing, it will find potential in pattern recognition, particularly, for infrared remote sensing.

Medicinal Plant Leaf Extract and Pure Flavonoid Mediated Green Synthesis of Silver Nanoparticles and their Enhanced Antibacterial Property

The rewards of using plants and plant metabolites over other biological methods for nanoparticle synthesis have fascinated researchers to investigate mechanisms of metal ions uptake and bio-reduction by plants. Here, green chemistry were employed for the synthesis of silver nanoparticles (AgNPs) using leaf extracts of Ocimum Sanctum (Tulsi) and its derivative quercetin (flavonoid present in Tulsi) separately as precursors to investigate the role of biomolecules present in Tulsi in the formation of AgNPs from cationic silver under different physicochemical conditions such as pH, temperature, reaction time and reactants concentration. The size, shape, morphology, and stability of resultant AgNPs were investigated by optical spectroscopy (absorption, photoluminescence (PL), PL-lifetime and Fourier transform infrared), X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). The enhanced antibacterial activity of AgNPs against E-Coli gram-negative bacterial strains was analyzed based on the zone of inhibition and minimal inhibitory concentration (MIC) indices. The results of different characterization techniques showed that AgNPs synthesized using both leaf extract and neat quercetin separately followed the same optical, morphological, and antibacterial characteristics, demonstrating that biomolecules (quercetin) present in Tulsi are mainly responsible for the reduction of metal ions to metal nanoparticles.

Gabor optical coherence tomographic angiography (GOCTA) (Part I): human retinal imaging in vivo.

Recently, parallel high A-line speed and wide field imaging for optical coherence tomography angiography (OCTA) has become more prevalent, resulting in a dramatic increase of data quantity which poses a challenge for real time imaging even for GPU in data processing. In this manuscript, we propose a new OCTA processing technique, Gabor optical coherence tomographic angiography (GOCTA), for label-free human retinal angiography imaging. In spectral domain optical coherence tomography (SDOCT), k-space resampling and Fourier transform (FFT) are required for the entire data set of interference fringes to calculate blood flow information in previous OCTA algorithms, which are computationally intensive. As adults' eye anterior-posterior radii are nearly constant, only 3 A-scan lines need to be processed to obtain the gross orientation of the retina by using a sphere model. Subsequently, the en face microvascular images can be obtained by using the GOCTA algorithm from interference fringes directly without the steps of k-space resampling, numerical dispersion compensation, FFT, and maximum (mean) projection, resulting in a significant improvement of the data processing speed by 4 to 20 times faster than the existing methods. GOCTA is potentially suitable for SDOCT systems in en face preview applications requiring real-time microvascular imaging.

An experimental water line list at 1950 K in the 6250–6670 cm[formula omitted] region

An absorption spectrum of H216O at 1950 K is recorded in a premixed methane/air flat flame using a cavity-enhanced optical frequency comb-based Fourier transform spectrometer. 2417 absorption lines are identified in the 6250–6670 cm−1 region with an accuracy of about 0.01 cm−1. Absolute line intensities are retrieved using temperature and concentration values obtained by tunable diode laser absorption spectroscopy. Line assignments are made using a combination of empirically known energy levels and predictions from the new POKAZATEL variational line list. 2030 of the observed lines are assigned to 2937 transitions, once blends are taken into account. 126 new energy levels of H216O are identified. The assigned transitions belong to 136 bands and span rotational states up to J=27.

Study of TiO2 in anatase form on selected properties of new aliphatic-aromatic imines with bent shape towards organic electronics

ABSTRACTTwo bent-shaped imines (9E)-N-(3-((E)-(4-hexadecylphenylimino)methyl)benzylidene)-4-hexadecylbenzenamine (SL1) and (10E)-N-(3-((E)-(4-(perfluorooctyl)phenylimino)methyl)benzylidene)-4-(perfluorooctyl)benzenamine (SL2) were prepared by condensation reaction in N,N-dimethylacetamide to study their thermal, structural and electrochemical properties, as well as their mixtures with titanium dioxide. Chemical structure, temperature and TiO2 influences on the phase transition temperatures, enthalpy, texture and molecular dynamics of both imines were investigated by differential scanning calorimetry, polarising optical microscopy and Fourier transform middle-infrared absorption spectroscopy during heating and cooling. Changes in the surface morphology of the imines and their mixtures with TiO2 were registered by atomic force microscopy. X-ray study showed the tendency to form lamellas in the case of SL2 as an effect of the presence of two terminal perfluorinated alkyl chains connected to a polar mobile aromatic core, which resulted in microsegregation. Additionally, TiO2 influences the energy gap and HOMO–LUMO levels of imines as was detected by cyclic voltammetry. Finally, devices with two types of architectures, such as ITO/TiO2/SL1(or P3HT)/Au and ITO/TiO2/SL1:P3HT/Au were constructed and investigated under irradiation intensity of 97.7 mW/cm2.

An optical Fourier transform coprocessor with direct phase determination

The Fourier transform is a ubiquitous mathematical operation which arises naturally in optics. We propose and demonstrate a practical method to optically evaluate a complex-to-complex discrete Fourier transform. By implementing the Fourier transform optically we can overcome the limiting O(nlogn) complexity of fast Fourier transform algorithms. Efficiently extracting the phase from the well-known optical Fourier transform is challenging. By appropriately decomposing the input and exploiting symmetries of the Fourier transform we are able to determine the phase directly from straightforward intensity measurements, creating an optical Fourier transform with O(n) apparent complexity. Performing larger optical Fourier transforms requires higher resolution spatial light modulators, but the execution time remains unchanged. This method could unlock the potential of the optical Fourier transform to permit 2D complex-to-complex discrete Fourier transforms with a performance that is currently untenable, with applications across information processing and computational physics.

Hybrid optical-digital system of texture recognition with liquid crystal input device

The results of experimental research of working hybrid optical-digital image recognition system based on features extracted from Fourier spectra are presented. To form the features an optical Fourier processor with liquid-crystal input device is used. Recognition is carried out with computer (PC) using a neural network algorithm. The possibility of applying the developed system for recognition of the terrain images obtained by aerial photography is shown.

Optical frequency comb Fourier transform spectroscopy with sub-nominal resolution and precision beyond the Voigt profile

Broadband precision spectroscopy is indispensable for providing high fidelity molecular parameters for spectroscopic databases. We have recently shown that mechanical Fourier transform spectrometers based on optical frequency combs can measure broadband high-resolution molecular spectra undistorted by the instrumental line shape (ILS) and with a highly precise frequency scale provided by the comb. The accurate measurement of the power of the comb modes interacting with the molecular sample was achieved by acquiring single-burst interferograms with nominal resolution matched to the comb mode spacing. Here we describe in detail the experimental and numerical steps needed to achieve sub-nominal resolution and retrieve ILS-free molecular spectra, i.e. with ILS-induced distortion below the noise level. We investigate the accuracy of the transition line centers retrieved by fitting to the absorption lines measured using this method. We verify the performance by measuring an ILS-free cavity-enhanced low-pressure spectrum of the 3ν1 + ν3 band of CO2 around 1575 nm with line widths narrower than the nominal resolution. We observe and quantify collisional narrowing of absorption line shape, for the first time with a comb-based spectroscopic technique. Thus retrieval of line shape parameters with accuracy not limited by the Voigt profile is now possible for entire absorption bands acquired simultaneously.

Preparation of Conductive Polymer Graphite (PG) Composites

The preparation of conductive polymer graphite (PG) composites thin film is described. The thickness of the PG composites due to slip casting method was set approximately ~0.1 mm. The optical microscope (OM) and fourier transform infra-red spectroscopy (FTIR) has been operated to distinguish the structure–property relationships scheme of PG composites. It shows that the graphite is homogenously dispersed in polymer matrix composites. The electrical characteristics of the PG composite were measured at room temperature and the electrical conductivity (σ) was discovered with respect of its resistivity (Ω). By achieving conductivity of 103 S/m, it is proven that at certain graphite weight loading (PG20, PG25 and PG30) attributes to electron pathway in PG composites.

Generation of One-Dimensional Terahertz Airy Beam by Three-Dimensional Printed Cubic-Phase Plate

We first present the one-dimensional (1-D) terahertz (THz) Airy beam with a 0.3-THz continuous wave. The required phase modulation and the optical Fourier transform are implemented with a 3-D printed cubic-phase plate (CPP) and a cylindrical lens, respectively. According to the parameter of the designed CPP, we numerically calculate the intensity distributions of the 1-D THz Airy beam in the free space. The experimental results show a good accordance with the theoretical ones. Additionally, by blocking part of the generated 1-D Airy beam with a metal screen, the beam exhibits a self-healing property, i.e., tends to reform during propagation.

Acousto-optic method of spatial frequency filtration based on diffraction of two eigenmodes of a crystal

A method is proposed for two-dimensional spatial frequency filtration based on acousto-optic (AO) diffraction of two eigenmodes of a crystal on a single acoustic wave. It is shown that AO filters, based on the use of such diffraction, ensure the enhancement of the two-dimensional image edge during its optical Fourier processing. The main theoretical conclusions are experimentally confirmed using an AO paratellurite filter.

Perceptual Crosstalk Prediction on Autostereoscopic 3D Display

Perceptual crosstalk prediction for autostereoscopic 3D displays is of fundamental importance in determining the level of quality perceived by humans in terms of the display performance and the 3D viewing experience. However, no robust framework exists to quantify perceptual crosstalk while taking into account the hardware structure of a display as well as its content characteristics via content analysis. In this paper, we present a 3D perceptual crosstalk predictor (3D-PCP) that can be used to predict crosstalk in a unique way when viewing autostereoscopic 3D displays. 3D-PCP captures hardware features using an optical Fourier transform-light measurement device and content features through content analysis based on information theory. By deriving the disparity, luminance, color, and texture maps, this approach defines the visual entropy, mutual information, and relative entropy in order to investigate the influences of the 3D scene characteristics on perceptual crosstalk. The experimental results demonstrate that the 3D-PCP output is highly correlated with subjective scores.

Efficacy of Irradiated Bioactive Glass 45S5 on Attenuation of Microbial Growth and Eradication of Biofilm from AISI 316 L Discs: In-vitro Study

Bacterial infection associated with medical implants remains a serious and costly drawback with both temporary and permanent consequences. Recently, some bioactive glasses have been found to show the antibacterial effect when interacting with bacteria. This study assessed the antibacterial activity of the bioactive glass (B.G.) based on 45S5 bioactive glass before and after treatment with gamma irradiation against multi-drug resistant microorganisms commonly involved in osteomyelitis. 45S5 glass which was synthesized by a melting technique with particle size < 45 μm was characterized by optical absorption, optical band gap and Fourier Transform Infrared Spectroscopy (FTIR) before and after exposure to gamma irradiation. From the optical absorption, the optical band gap can be calculated. The antimicrobial activity of 45S5 glass irradiated at 25 and 50 kGy against some pathogenic strains was evaluated. The results revealed that irradiated 45S5 bioactive glass causes a reduction in the number of survivors of the tested strains rather than the non-irradiated one. The microbial counts decreased by increasing the pH. The results also indicated that the colony forming units (cfu) decreased by one log cycle in nutrient broth (NB) medium and three log cycles in simulated body fluid (SBF). Scanning electron microscopy showed cell shrinkage and membrane damage after exposure of the glass to irradiation. So, an alkaline pH and SBF media along with gamma irradiation are considered as the most preferable conditions affecting the antimicrobial activity of the irradiated 45S5 glass and have the ability to eradicate the biofilm produced by P. aeruginosa on AISI 316 L discs which are used in joint replacement.

Effect of Cooling Rates on Shape and Crystal Size Distributions of Mefenamic Acid Polymorph in Ethyl Acetate

This study investigate the effect of cooling rates on mefenamic acid crystallisation in ethyl acetate. The cooling rate was varied from 0.2 to 5 °C/min. The in-line conductivity system and turbidity system were employed to detect the onset of the crystallization process. The crystals produced were analysed using optical microscopy and Fourier transform infrared spectroscopy (FTIR). It was found that the crystals produced at different cooling rates were needle-like and exhibit polymorphic form type I. However, the aspect ratio and crystal size distributions were varied with the increased of cooling rate. A high crystals aspect ratio and narrower CSD (100–900 μm) was obtained at cooling rate of 0.5 °C/min. Thus, can be suggested as the most suitable cooling rate for crystallization of mefenamic acid in ethyl acetate.

Synthesis of transparent oil dispersion of monodispersed calcium carbonate nanoparticles with high concentration

The preparation of monodispersed inorganic nanoparticles is of great interest for many applications. In this article, transparent oil dispersion of monodispersed amorphous CaCO3 nanoparticles with high concentration and long‐term stability were controllably prepared by a reverse microemulsion method. The effects of the addition amount of extra minute water and (NH4)2CO3 as novel assistant promoter, reaction temperature, Ca(OH)2/CaO mole ratio were explored. The optimum synthesis conditions were achieved. The as‐prepared transparent oil nanodispersion had a good monodispersity, a uniform particle size of 8–10 nm, a high stability of over 12 months, a high solid content of 38 wt% (Ca content of about 15.5 wt%) and a high total base number of 416 mgKOH/g. The preparation process was further investigated by polarized optical microscope and Fourier transform infrared. This nanodispersion will find a promising applicability as an excellent nanodetergent in the fields of automobile and marine lubricants. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3663–3669, 2017

Autofocusing Airy beams generated by all-dielectric metasurface for visible light.

Conventional method to generate autofocusing Airy (AFA) beam involves the optical Fourier transform (FT) system, which has a fairly long working distance due to the focal length of FT lens, presence of spatial light modulator (SLM) and auxiliary total reflection mirrors. Here, we propose an extremely compact design to generate high-efficiency AFA beam at visible frequency by using metasurface which is composed of a single layer array of amorphous titanium dioxide (TiO2) elliptical nanofins sitting on the fused-silica substrate. Numerical simulations show that the designed structures are capable of precisely controlling the deflection of Airy beam and tuning the focal length of AFA beam. We further numerically demonstrate that the phase modulation of AFA beam could combine with the concept of vortex light field to produce vortical AFA beam. We anticipate that such device can be useful in the ultra-compact integrated optic system, biomedical nanosurgery and optical trapping applications.

Redshift in the UV emission and curtailment in optical band gap of Manganese doped Zinc oxide thin films

A redshift in the optical band gap of Manganese doped Zinc Oxide (Zn1−x Mn x O) thin films has been obtained. The Zn1−x Mn x O thin films obtained by sol gel spin coating method exhibit a 7.14% decrease in the optical band gap. The band gap narrows down from 3.22 eV to as low as 2.99 eV as the concentration of the dopant is increased from x = 0 to x = 0.6. The photoluminescence spectra also show a redshift of 106 meV in the ultraviolet emission peak i.e. NBE emission as the concentration of Manganese is increased in the thin films. The polycrystalline Zinc Oxide thin films with wurtzite hexagonal structure have been probed into with the help of X-ray diffraction spectroscopy, optical transmission spectroscopy and Fourier transforms infrared spectroscopy. Scanning electron microscopy revealed the granular surface of the Mn doped ZnO thin films.

Influence of surface functionalization on the gas sensing characteristics of ZnO nanorhombuses

Spectral characteristics of clad modified fiber optic gas sensor are studied for various concentrations (0–400 ppm) of acetone, ammonia and ethanol at room temperature. The ZnO nanorhombuses were synthesized by co-precipitation technique. The synthesized ZnO nanorhombuses were characterized by X-ray diffraction, high resolution transmission electron microscope, optical absorption studies and Fourier transform infrared spectroscopy. The analysis confirms the formation of ZnO nanorhombuses with wurtzite structure. The synthesized ZnO nanorhombuses were surface functionalized with thiourea to study the impact of functionalization on gas sensing characteristics. The small portion of cladding layer was replaced with nanorhombuses to study the gas sensing characteristics. It shows that the synthesized ZnO nanorhombuses have better selectivity towards acetone than ammonia and ethanol. The thiourea functionalized nanorhombuses showed enhanced sensitivity and fast response compared to the pristine ZnO nanorhombuses. Further, the wavelength dependent sensitivity analysis show that the fiber optic acetone sensor can be operated in visible wavelength with higher sensitivity and in infrared wavelength with moderate sensitivity.

Nonlinear mode switching in lithium niobate nanowaveguides to control light directionality.

The ability of nanowaveguides to confine and guide light has been applied for developing optical applications such as nanolasers, optical switching and localized imaging. These and others applications can be further complemented by the optical control of the guided modes within the nanowaveguide, which in turn dictates the light emission pattern. It has been shown that the light directionality can be shaped by varying the nanowire cross-sections. Here, we demonstrate that the directionality of the light can be modified using a single nanowaveguide with a nonlinear phenomenon such as second-harmonic generation. In individual lithium niobate nanowaveguides, we use second-harmonic modal phase-matching and we apply it to switch the guided modes within its sub-micron cross-section. In doing so, we can vary the light directionality of the generated light from straight (0° with respect to the propagation direction) to large spread angles (almost 54°). Further, we characterize the directionality of the guided light by means of optical Fourier transformation and show that the directionality of the guided light changes for different wavelengths.