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Results for “optical interference”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nonlinear optical spectra having characteristics of Fano interferences in coherently coupled lowest exciton biexciton states in semiconductor quantum dots

Optical nonlinear effects are examined using a two-color micro-photoluminescence (micro-PL) method in a coherently coupled exciton-biexciton system in a single quantum dot (QD). PL and photoluminescence excitation spectroscopy (PLE) are employed to measure the absorption spectra of the exciton and biexciton states. PLE for Stokes and anti-Stokes PL enables us to clarify the nonlinear optical absorption properties in the lowest exciton and biexciton states. The nonlinear absorption spectra for excitons exhibit asymmetric shapes with peak and dip structures, and provide a distinct contrast to the symmetric dip structures of conventional nonlinear spectra. Theoretical analyses with a density matrix method indicate that the nonlinear spectra are caused not by a simple coherent interaction between the exciton and biexciton states but by coupling effects among exciton, biexciton and continuum states. These results indicate that Fano quantum interference effects appear in exciton-biexciton systems at QDs and offer important insights into their physics.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optically resonant magneto-electric cubic nanoantennas for ultra-directional light scattering

Cubic dielectric nanoparticles are promising candidates for futuristic low-loss, ultra-compact, nanophotonic applications owing to their larger optical coefficients, greater packing density, and relative ease of fabrication as compared to spherical nanoparticles; besides possessing negligible heating at nanoscale in contrast to their metallic counterparts. Here, we present the first theoretical demonstration of azimuthally symmetric, ultra-directional Kerker's-type scattering of simple dielectric nanocubes in visible and near-infrared regions via simultaneous excitation and interference of optically induced electric- and magnetic-resonances up to quadrupolar modes. Unidirectional forward-scattering by individual nanocubes is observed at the first generalized-Kerker's condition for backward-scattering suppression, having equal electric- and magnetic-dipolar responses. Both directionality and magnitude of these unidirectional-scattering patterns get enhanced where matching electric- and magnetic-quadrupolar responses spectrally overlap. While preserving azimuthal-symmetry and backscattering suppression, a nanocube homodimer provides further directionality improvement for increasing interparticle gap, but with reduced main-lobe magnitude due to emergence of side-scattering lobes from diffraction-grating effect. We thoroughly investigate the influence of interparticle gap on scattering patterns and propose optimal range of gap for minimizing side-scattering lobes. Besides suppressing undesired side-lobes, significant enhancement in scattering magnitude and directionality is attained with increasing number of nanocubes forming a linear chain. Optimal directionality, i.e., the narrowest main-scattering lobe, is found at the wavelength of interfering quadrupolar resonances; whereas the largest main-lobe magnitude is observed at the wavelength satisfying the first Kerker's condition. These unique optical properties of dielectric nanocubes thus can revolutionize their applications at visible and near-infrared regions in the fields of nanoantennas, nanolasers, photovoltaics, and even in biomedicine.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Demonstration of a Fresnel axicon

We design and manufacture a Fresnel axicon (fraxicon) that generates a quasi-diffraction-free/Bessel beam with a large depth of field. The novel optical element is characterized with both coherent and incoherent light, and its behavior is compared with that of a classical axicon. While the fraxicon exhibits a strong interference pattern in the on-axis intensity distribution, it can be smoothed out when using broadband light, partial spatial coherence light, or by period randomization. As inexpensive, compact/lightweight, and low-absorption elements, fraxicons may find applications in imaging, illumination, and situations where low absorption and dispersion are important.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

“MODAL NOISE” IN SINGLE-MODE FIBERS: A CAUTIONARY NOTE FOR HIGH PRECISION RADIAL VELOCITY INSTRUMENTS

Exploring the use of single-mode fibers (SMFs) in high precision Doppler spectrometers has become increasingly attractive since the advent of diffraction-limited adaptive optics systems on large-aperture telescopes. Spectrometers fed with these fibers can be made significantly smaller than typical “seeing-limited” instruments, greatly reducing cost and overall complexity. Importantly, classical mode interference and speckle issues associated with multi-mode fibers, also known as “modal noise,” are mitigated when using SMFs, which also provide perfect radial and azimuthal image scrambling. However, SMFs do support multiple polarization modes, an issue that is generally ignored for larger-core fibers given the large number of propagation modes. Since diffraction gratings used in most high resolution astronomical instruments have dispersive properties that are sensitive to incident polarization changes, any birefringence variations in the fiber can cause variations in the efficiency profile, degrading illumination stability. Here we present a cautionary note outlining how the polarization properties of SMFs can affect the radial velocity (RV) measurement precision of high resolution spectrographs. This work is immediately relevant to the rapidly expanding field of diffraction-limited, extreme precision RV spectrographs that are currently being designed and built by a number of groups.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Visibility bound caused by a distinguishable noise particle

We investigate how the distinguishability of a 'noise' particle degrades interference of the 'signal' particle. The signal, represented by an equatorial state of a photonic qubit, is mixed with noise, represented by another photonic qubit, via linear coupling on a beam splitter. We report on the degradation of the signal photon interference depending on the degree of indistinguishability between the signal and noise photons. When the photons are completely distinguishable in principle but technically indistinguishable, the visibility drops to the value 1/{radical}(2). As the photons become more indistinguishable, the maximal visibility increases and reaches the unit value for completely indistinguishable photons. We have examined this effect experimentally using a setup with a fiber-optics two-photon Mach-Zehnder interferometer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Response of a matrix photodetector into components of an optical signal with different spatial frequencies

We have used the method of direct evaluation of energy incident on each pixel of a photosensitive array to assess the distortions of a matrix photodetector response into a sinusoidal spatial signal. Using the data obtained, we have formulated recommendations for selecting a resolution of a matrix photodetector as a function of a maximum spatial frequency in the recorded interference pattern, as well as for matching of the resolutions of an objective and a photodetector of a digital camera or camcorder. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Application of STEM/EELS to Plasmon-Related Effects in Optical Spectroscopy

The last decade has seen an explosion in the study of plasmonic materials, with current applications including surface-enhanced spectroscopy, imaging beyond the diffraction limit, solar energy harvesting, and ultrasensitive detection. This proposal utilizes electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) to explore the near-field enhancements encountered upon excitation of the localized surface plasmon resonance. In particular we have studied Fano interferences using optical and electron energy-loss spectroscopies (EELS). Single silver nanocubes were utilized in this study due to the substrate-mediated hybridization of the primitive dipolar and quadrupolar plasmon modes that give rise to the Fano phenomenon. The cube at substrate system provides a unique opportunity to study the plasmonic energy transfer from metallic nanoparticles to neighboring materials, which is an essential component of plasmon-enhanced solar harvesting devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Precision loss measurements in short lengths of optical fibre by reflectometry without using Rayleigh scattering

To improve accuracy of light attenuation measurements in optical fibres, especially in short ones, tens and hundreds of metres in length, we propose rejecting a conventional reflectometric approach based on Rayleigh scattering intensity measurements. To this end, we propose for the first time the use of boson peaks in Raman scattering, which, on the one hand, produce no interference effects and no related noise in reflectograms, and, on the other, lie within the C-band. Even at a fibre length as short as 50 m, the attenuation measurement error does not exceed 0.002 dB km{sup −1}. We demonstrate the possibility of compensating for the temperature variation of boson peak intensity by concurrently obtaining a reflectogram for the anti-Stokes line of the fundamental Raman band. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Near-IR laser-based spectrophotometer for comparative analysis of isotope content of CO{sub 2} in exhale air samples

We present a laser spectrophotometer aimed at high-accuracy comparative analysis of content of {sup 12}CO{sub 2} and {sup 13}CO{sub 2} isotope modifications in the exhale air samples and based on a tunable near-IR diode laser (2.05 {mu}m). The two-channel optical scheme of the spectrophotometer and the special digital system for its control are described. An algorithm of spectral data processing aimed at determining the difference in the isotope composition of gas mixtures is proposed. A few spectral regions (near 4880 cm{sup -1}) are determined to be optimal for analysis of relative content of {sup 12}CO{sub 2} and {sup 13}CO{sub 2} in the exhale air. The use of the proposed spectrophotometer scheme and the developed algorithm makes the results of the analysis less susceptible to the influence of the interference in optical elements, to the absorption in the open atmosphere, to the slow drift of the laser pulse envelope, and to the offset of optical channels. The sensitivity of the comparative analysis of the isotope content of CO{sub 2} in exhale air samples, achieved using the proposed scheme, is estimated to be nearly 0.1 Per-Mille-Sign .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Comparative performance analysis of relative humidity sensor based on intermodal interference using tapered square no-core optical fiber and tapered cylindrical optical fiber

This work presents the computational evaluation of a new model for relative humidity sensor based on the principle of intermodal interference using a square-section no-core tapered optical fiber compared to a classical cylindrical tapered optical fiber sensor. Attempting at a new application of this type of sensor, simulations were carried out in the range of up to 60% of relative humidity, the main interest range of the pharmaceutical industry. Several materials were used in its modeling and an analysis was developed in its constructive dimensions, in order to verify the influence of each of them on the sensor performance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Realization of spin wave switch for data processing

In this work, experimental data on a spin wave switch based on spin wave interference is reported. The switch is a three terminal device where spin wave propagation between the source and the drain is modulated by the control spin wave signal. The prototype is a micrometer scale device based on Y 3 Fe 2 (FeO 4 ) 3 film. The output characteristics show the oscillation of the output spin wave signal as a function of the phase difference between the source and the drain spin wave signals. The On/Off ratio of the prototype exceeds 20 dB at room temperature. The utilization of phase in addition to amplitude for information encoding offers an innovative route towards multi-state logic circuits. The advantages and shortcomings of spin wave switches are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Fe{sub 3}O{sub 4} and CdS based bifunctional core–shell nanostructure

Highlights: ► First report on a room temperature aqueous process for growth of a hybrid core shell nanostructure containing a magnetic core and a semiconducting shell. ► Formation of distinct core shell nanostructure revealed by high resolution transmission electron microscopy. ► A bifunctional nature combining magnetic as well as photoresponce for the as synthesised core shell nanostructures demonstrated. ► A tendency towards self organisation of the core–shell nanostructure. ► Possible applications including purification and isolation of biological materials, drug delivery system, bio-labels, spintronics, etc. -- Abstract: A room temperature solution process for synthesis of Fe{sub 3}O{sub 4} nanoparticles and their hybrid core shell nanostructures using CdS as the shell material has been described. The as grown particles have been characterised using XRD, Rietveld refinement, high resolution transmission electron microscopy, atomic force microscopy, superconducting quantum interference device, optical absorbance and photoluminescence spectroscopy. A superparamagnetic response revealed from the magnetisation measurements of the as synthesised magnetite nanoparticles was retained even after the growth of the CdS shell. From luminescence and high resolution atomic force microscopy measurements, it is shown that the core–shell structures advantageously combine magnetic as well as fluorescence response with a tendency towards self-organization.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Assembly of Building Blocks by Double-End-Anchored Polymers in the Dilute Regime Mediated by Hydrophobic Interactions at Controlled Distances

Hierarchical assembly of building blocks via competing, orthogonal interactions is a hallmark of many of nature’s composite materials that do not require highly specific ligand-receptor interactions. To mimic this assembly mechanism requires the development of building blocks capable of tunable interactions. In the present work, we explored the interplay between repulsive (steric and electrostatic) and attractive hydrophobic forces. The designed building blocks allow hydrophobic forces to effectively act at controlled, large distances, to create and tune the assembly of membrane-based building blocks under dilute conditions and affect their interactions with cellular membranes via physical cross-bridges. Specifically, we employed double-end-anchored poly(ethylene glycol)s (DEA-PEGs)—hydrophilic PEG tethers with hydrophobic tails on both ends. Using differential-interference-contrast optical microscopy, synchrotron small angle X-ray scattering (SAXS), and cryogenic electron microscopy, we investigated the ability of DEA-PEGs to mediate assembly in the dilute regime on multiple length scales and on practical time scales. The PEG length, anchor hydrophobicity, and molar fraction of DEA-PEG molecules within a membrane strongly affect the assembly properties. Additional tuning of the intermembrane interactions can be achieved by adding repulsive interactions via PEG-lipids (steric) or cationic lipids to the DEA-PEG-mediated attractions. Further, while the optical and electron microscope imaging methods provided qualitative evidence of the ability of DEA-PEGs to assemble liposomes, the SAXS measurements and quantitative line-shape analysis in dilute preparations demonstrated that the ensemble average of loosely organized liposomal assemblies maintains DEA-PEG concentration-dependent tethering on defined nanometer length scales. For cationic liposome–DNA nanoparticles (CL–DNA NPs), aggregation induced by DEA-PEGs decreased internalization of NPs by cells, but tuning the DEA-PEG-induced attractions by adding repulsive steric interactions via PEG-lipids limited aggregation and increased NP uptake. However, confocal microscopy imaging together with colocalization studies with Rab11 and LysoTracker as markers of intracellular pathways showed that modifying CL–DNA NPs with DEA-PEGs alters their interactions with the plasma and endosomal membranes.

- x-ray scattering↗
DOE OSTI2020

Experimental demonstration of broadband solar absorption beyond the lambertian limit in certain thin silicon photonic crystals

The tantalizing possibility of 31% solar-to-electric power conversion efficiency in thin film crystalline silicon solar cell architectures relies essentially on solar absorption well beyond the Lambertian light trapping limit (Bhattacharya and John in Nat Sci Rep 9:12482, 2019). Up to now, no solar cell architecture has exhibited above-Lambertian solar absorption, integrated over the broad solar spectrum. In this work, we experimentally demonstrate two types of photonic crystal (PhC) solar cells architectures that exceed Lambertian light absorption, integrated over the entire 300–1,200 nm wavelength band. These measurements confirm theoretically predicted wave-interference-based optical resonances associated with long lifetime, slow-light modes and parallel-to-interface refraction. These phenomena are beyond the realm of ray optics. Using two types of 10-μm thick PhC’s, first an Inverted Pyramid PhC with lattice constant a= 2,500 nm and second a Teepee PhC with a = 1,200 nm, we observe solar absorption well beyond the Lambertian limit over λ = 950–1,200 nm. Our absorption measurements correspond to the maximum-achievable-photocurrent-density (MAPD), under AM1.5G illumination at 4-degree incident angle, 41.29 and 41.52 mA/cm2 for the Inverted Pyramid and Teepee PhC, respectively, in agreement with wave-optics, numerical simulations. Both of these values exceed the MAPD (= 39.63 mA/cm2) corresponding to the Lambertian limit for a 10-μm thick silicon for solar absorption over the 300–1,200 nm band.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Quantum interference and control of the optical response in quantum dot molecules

We discuss the optical response of a quantum molecule under the action of two lasers fields. Using a realistic model and parameters, we map the physical conditions to find three different phenomena reported in the literature: the tunneling induced transparency, the formation of Autler-Townes doublets, and the creation of a Mollow-like triplet. We found that the electron tunneling between quantum dots is responsible for the different optical regime. Our results not only explain the experimental results in the literature but also give insights for future experiments and applications in optics using quantum dots molecules.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Interfacial stability of ultrathin films of magnetite Fe 3 O 4 (111) on Al 2 O 3 (001) grown by ozone-assisted molecular-beam epitaxy

Thin films of iron oxides including magnetite (Fe 3 O 4 ) and hematite (α-Fe 2 O 3 ) have many important applications. Both forms of oxide can occur naturally during film growth by iron deposition under various oxidation environment; an important issue is to understand and control the process resulting in a single-phase film. We have performed in-situ real-time studies using x-ray diffraction of such film growth on sapphire (001) under pure ozone by monitoring the (00L) rod. Stable magnetite growth can be maintained at growth temperatures below 600° C up to a certain critical film thickness, beyond which the growth becomes hematite. The results demonstrate the importance of interfacial interaction in stabilizing the magnetite phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Simple imaging for the diamond anvil cell: Applications to hard-to-reach places

The employment of high-pressure gases as a pressure-transmitting medium, sample, or reactant for diamond anvil cell experiments is widespread. As a pressure transmitter, high-pressure gases are crucial to forming quasi-hydrostatic compression atmospheres for samples inside the uniaxially driven cell. We describe an optical design for forming high-resolution images of the gasket and sample chamber of the diamond anvil cell under high gas pressures in a gas loading apparatus. Our design is simple, is of low-cost, and may be easily adapted to suit gas loading apparatus of any design, as well as other common hard-to-reach environments in diamond anvil cell experiments, i.e., those with large stand-off distances, such as cryostats.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗