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Results for “diffractive optics”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Measuring charge carrier mobility in photovoltaic devices with micron-scale resolution

We present a charge-extraction technique, micron-scale charge extraction by linearly increasing voltage, which enables simultaneous spatially resolved measurements of charge carrier mobility and photocurrent in thin-film photovoltaic devices with micron-scale resolution. An intensity-modulated laser with beam diameter near the optical diffraction limit is scanned over the device, while a linear voltage ramp in reverse bias is applied at each position of illumination. We calculate the majority carrier mobility, photocurrent, and number of photogenerated charge carriers from the resulting current transient. We demonstrate this technique on an organic photovoltaic device, but it is applicable to a wide range of photovoltaic materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Solvent immersion nanoimprint lithography of fluorescent conjugated polymers

Solvent immersion imprint lithography (SIIL) was used to directly nanostructure conjugated polymer films. The technique was used to create light-emitting diffractive optical elements and organic semiconductor lasers. Gratings with lateral features as small as 70 nm and depths of ∼25 nm were achieved in poly(9,9-dioctylfluorenyl-2,7-diyl). The angular emission from the patterned films was studied, comparing measurement to theoretical predictions. Organic distributed feedback lasers fabricated with SIIL exhibited thresholds for lasing of ∼40 kW/cm{sup 2}, similar to those made with established nanoimprint processes. The results show that SIIL is a quick, convenient and practical technique for nanopatterning of polymer photonic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Local measurement of bulk thermal diffusivity using photothermal radiometry

Here, an experimental methodology using photothermal radiometry is developed for the accurate measurement of bulk thermal diffusivity of nuclear fuels and materials irradiated to high doses. Under these conditions, nuclear fuels, such as uranium oxide, and moderator materials, such as graphite, become friable, which requires characterization techniques that can accommodate irregularly shaped fragments. Photothermal radiometry, a good candidate for this application, involves locally heating a sample by using a laser and measuring the temperature field by monitoring blackbody radiation. The interaction volume for this study, less than a millimeter, is carefully chosen to sample a statistically significant number of large-scale structural features, such as pores and gas filled bubbles, and is small enough that the sample fragments can be treated as a thermal half-space. The thermal diffusivity standards considered in this study cover a range of thermal diffusivities representative of both fresh and spent nuclear fuels. We also consider a sample having a porous microstructure representative of large-scale structures found in materials irradiated to high doses. Our measurement methodology circumvents complex thermal wave models that address optical diffraction, nonlinear transfer function associated with blackbody radiation, and finite sample size effects. Consequently, the large measurement uncertainty associated with modeling these effects can be avoided. While the emphasis here is on nuclear fuels and materials, this measurement approach is well suited to measure thermal transport in a variety of technologically important materials associated with advanced synthesis techniques. Examples range from small, exotic single crystals grown using hydrothermal growth techniques to additively manufactured components having complex geometries.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A wave model of refraction of laser beams with a discrete change in intensity in their cross section and their application for diagnostics of extended nonstationary phase objects

A beam model with a discrete change in the cross-sectional intensity is proposed to describe refraction of laser beams formed on the basis of diffractive optical elements. In calculating the wave field of the beams of this class under conditions of strong refraction, in contrast to the traditional asymptotics of geometric optics which assumes a transition to the infinite limits of integration and obtaining an analytical solution, it is proposed to calculate the integral in the vicinity of stationary points. This approach allows the development of a fast algorithm for correct calculation of the wave field of the laser beams that are employed in probing and diagnostics of extended optically inhomogeneous media. Examples of the algorithm application for diagnostics of extended nonstationary objects in liquid are presented. (laser beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Highly sensitive nonlinear luminescent ceramics for volumetric and multilayer data carriers

The interaction of optical ceramics based on wide-bandgap crystals with near-IR femtosecond laser radiation is studied experimentally. The formation of luminescent centres in LiF and MgF{sub 2} ceramics under the action of single laser pulses is considered. Two interaction regimes are used. In the regime of low-aperture focusing of laser radiation (800 nm, 30 fs, 0.3 mJ), multiple selffocusing and filamentation in the samples are observed. The luminescent centres are formed in thin channels induced by light filaments. The average effective self-focusing length is ∼100 μm; the formation of luminescent centres begins at this length and ceases at a wavelength of about 380 mm. The luminescent trace (spur) induced by a single laser filament was ∼30 μm long and 1.3 μm in diameter. The second regime of light interaction with the sample was based on high-aperture focusing with a simultaneous decrease in the laser pulse energy. This led to the formation of single pits with a diameter smaller than the optical diffraction limit. The luminescent centres induced by the laser radiation were aggregated colour centres. The mechanism of their creation included the highly-nonlinear generation of electron – hole pairs in the filamentation region, their recombination with the formation of anion excitons and the decay of excitons into Fresnel defects by the Lushchik – Vitol – Hersh – Pooley mechanism, as well as their recharging, migration and aggregation. (laser applications and other topics in quantum electronics)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Highly multicolored light-emitting arrays for compressive spectroscopy

Miniaturized, multicolored light-emitting device arrays are promising for applications in sensing, imaging, computing, and more, but the range of emission colors achievable by a conventional light-emitting diode is limited by material or device constraints. In this work, we demonstrate a highly multicolored light-emitting array with 49 different, individually addressable colors on a single chip. The array consists of pulsed-driven metal-oxide-semiconductor capacitors, which generate electroluminescence from microdispensed materials spanning a diverse range of colors and spectral shapes, enabling facile generation of arbitrary light spectra across a broad wavelength range (400 to 1400 nm). When combined with compressive reconstruction algorithms, these arrays can be used to perform spectroscopic measurements in a compact manner without diffractive optics. As an example, we demonstrate microscale spectral imaging of samples using a multiplexed electroluminescent array in conjunction with a monochrome camera.

42 ENGINEERING↗
DOE OSTI2019

Large Aperture and Wedged Multilayer Laue Lens for X-ray Nanofocusing

Diffraction optics fabricated from multilayers offer an intriguing alternative to lithography-based zone plates due to their advantages of virtually limitless aspect ratio and extremely small feature size. However, other issues, intrinsic to thin-film deposition, such as film stress and deposition rate instability, for example, limit the total achievable aperture. Over the last decade, Multilayer Laue Lens (MLLs) have progressed from a mere curiosity with initial aperture sizes in the 3–10 μm range, to real beamline-deployed optics with apertures in the 40–50 μm range (X. Huang, et al., Scientific Reports 3, 3562 (2013); E. Nazaretski, et al., Rev. Sci. Instrum. 85, 033707 (2014); E. Nazaretski, et al., Journal of Synchrotron Radiation 24, 1113 (2017)). By optimizing deposition conditions and incorporating new materials, MLLs have now broken the 100 μm thickness milestone. A flat WSi 2 /Al–Si MLL with a deposition thickness of 102 μm, the largest MLL to date, is reviewed. New large aperture wedged MLLs (wMLL), which were first fabricated by APS in 2006 using the WSi 2 /Si material system, are presented which demonstrate high focusing efficiency across a broad energy range. Furthermore, these results confirm findings by other groups who have also independently fabricated wMLL (A. J. Morgan, et al., Scientific Reports 5, 9892 (2015); S. Bajt, et al., Nature Light: Science and Applications 7, 17162 (2017)) based on a similar material system.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Fast scanning in x-ray microscopy: the effects of offset in the central stop position

Scanning of lightweight circular diffractive optics, separate from central stops and apertures, is emerging as an approach to exploit advances in synchrotron x-ray sources. We consider the effects in a scanning microscope of offsets between the optic and its central stop and find that scan ranges of up to about half the diameter of the optic are possible with only about a 10% increase in the focal spot width. Finally, for large scanning ranges, we present criteria for the working distance between the last aperture and the specimen to be imaged.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Snapshot multifocal light field microscopy

Light field microscopy (LFM) is an emerging technology for high-speed wide-field 3D imaging by capturing 4D light field of 3D volumes. However, its 3D imaging capability comes at a cost of lateral resolution. In addition, the lateral resolution is not uniform across depth in the light field dconvolution reconstructions. To address these problems, here, we propose a snapshot multifocal light field microscopy (MFLFM) imaging method. The underlying concept of the MFLFM is to collect multiple focal shifted light fields simultaneously. We show that by focal stacking those focal shifted light fields, the depth-of-field (DOF) of the LFM can be further improved but without sacrificing the lateral resolution. Also, if all differently focused light fields are utilized together in the deconvolution, the MFLFM could achieve a high and uniform lateral resolution within a larger DOF. We present a house-built MFLFM system by placing a diffractive optical element at the Fourier plane of a conventional LFM. The optical performance of the MFLFM are analyzed and given. Both simulations and proof-of-principle experimental results are provided to demonstrate the effectiveness and benefits of the MFLFM. We believe that the proposed snapshot MFLFM has potential to enable high-speed and high resolution 3D imaging applications.

He, Kuan↗
DOE OSTI2021

Stabilization of the 81-channel coherent beam combination using machine learning

We develop a rapidly converging algorithm for stabilizing a large channel-count diffractive optical coherent beam combination. An 81-beam combiner is controlled by a novel, machine-learning based, iterative method to correct the optical phases, operating on an experimentally calibrated numerical model. A neural-network is trained to detect phase errors based on interference pattern recognition of uncombined beams adjacent to the combined one. Due to the non-uniqueness of solutions in the full space of possible phases, the network is trained within a limited phase perturbation/error range. This also reduces the number of samples needed for training. Simulations have proven that the network can converge in one step for small phase perturbations. When the trained neural-network is applied to a realistic case of 360 degree full range, an iterative scheme exploits random walking at the beginning, with the accuracy of prediction on phase feedback direction, to allow the neural-network to step into the training range for fast convergence. This neural-network-based iterative method of phase detection works tens of times faster than the commonly used stochastic parallel gradient descent approach (SPGD) using a single-detector and random dither when both are tested with random phase perturbations.

Wang, Dan↗
DOE OSTI2021

Maskless Fourier transform holography

Fourier transform holography is a lensless imaging technique that retrieves an object's exit-wave function with high fidelity. It has been used to study nanoscale phenomena and spatio-temporal dynamics in solids, with sensitivity to the phase component of electronic and magnetic textures. However, the method requires an invasive and labor-intensive nanopatterning of a holography mask directly onto the sample, which can alter the sample properties, forces a fixed field-of-view, and leads to a low signal-to-noise ratio at high resolution. In this work, we propose using wavefront-shaping diffractive optics to create a structured probe with full control of its phase at the sample plane, circumventing the need for a mask. We demonstrate in silico that the method can image nanostructures and magnetic textures and validate our approach with a visible light-based experiment. The method enables investigation of a plethora of phenomena at the nanoscale including magnetic and electronic phase coexistence in solids, with further uses in soft and biological matter research.

Keskinbora, Kahraman↗
DOE OSTI2016

Multiwavelength polarization-insensitive lenses based on dielectric metasurfaces with meta-molecules

Metasurfaces are nanostructured devices composed of arrays of subwavelength scatterers (or meta-atoms) that manipulate the wavefront, polarization, or intensity of light. Like most other diffractive optical devices, metasurfaces are designed to operate optimally at one wavelength. Here in this paper, we present a method for designing multiwavelength metasurfaces using unit cells with multiple meta-atoms, or meta-molecules. A transmissive lens that has the same focal distance at 1550 and 915 nm is demonstrated. The lens has a NA of 0.46 and measured focusing efficiencies of 65% and 22% at 1550 and 915 nm, respectively. With proper scaling, these devices can be used in applications where operation at distinct known wavelengths is required, like various fluorescence microscopy techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single-shot spatiotemporal plasma density measurements with a chirped probe pulse

In this work, we present the development and demonstration of a diagnostic for the measurement of the spatial and temporal evolution of plasma density in a single shot. Single-shot Advanced Plasma Probe HolographIc REconstruction (SAPPHIRE) utilizes a chirped probe pulse, a diffractive optical element, a self-referenced interferometer, and an interference bandpass filter to achieve high-fidelity electron density measurements suitable for underdense plasmas that exhibit cylindrical symmetry. The method overcomes limitations in conventional diagnostics, such as reliance on shot-to-shot reproducibility, while capturing plasma dynamics on picosecond timescales with micron-level spatial resolution. The capabilities of SAPPHIRE are demonstrated through measurements of laser-driven plasma channels in helium–nitrogen gas jets. SAPPHIRE demonstrates the formation and expansion of plasma channels in a single shot and the propagation of supersonic ionization fronts while revealing shot-to-shot variations in the plasma profiles. Experimental results are validated against theoretical models and scaling laws, underscoring the robustness and accuracy of this technique. By enabling ultrafast, high-resolution plasma diagnostics in a single exposure, SAPPHIRE represents a transformative advancement in plasma measurement technology.

Grace, Elizabeth S. [Lawrence Livermore National L↗
NASA NTRS1969

Acousto-optic tunable filter.

Electronically tunable lithium niobate optical filter utilizing collinear acousto-optic diffraction in anisotropic medium

Harris, S. E.↗
NASA NTRS1971

Methods of analyzing microsize particulate aerosols and contaminants.

Methods for analyzing atmospheric aerosols and particulate contaminants from natural and industrial sources are briefly described. Their development was spurred by interest in cosmic dust investigations. These methods make it possible to analyze individual particles ranging in size from 0.01 to 1000 microns for elemental and mineralogical content. The described methods include transmission electron microscopy, scanning electron microscopy, electron probe microanalysis, X-ray diffraction, optical mineralogy, and density measurement.

Blanchard, M. B.↗
NASA NTRS1972

Automated thematic mapping and change detection of ERTS-A images

The author has identified the following significant results. For the exploitation of the ERTS-1 images, both multispectral and spatial pattern recognition techniques are important. A multispectral recognition software program was successfully tested. A technique for the generation of resource boundaries has been successfully combined with terrain recognition software resulting in a regionalized terrain classification system. Digital registration of multispectral images has been achieved. Also, photointerpretation results from one test site are reported and the development of spatial terrain signatures from optical diffraction patterns is described.

Gramenopoulos, N.↗
NASA NTRS1972

Analysis of a dual-reflector antenna system using physical optics and digital computers

The application of physical-optics diffraction theory to a deployable dual-reflector geometry is discussed. The methods employed are not restricted to the Conical-Gregorian antenna, but apply in a general way to dual and even multiple reflector systems. Complex vector wave methods are used in the Fresnel and Fraunhofer regions of the reflectors. Field amplitude, phase, polarization data, and time average Poynting vectors are obtained via an IBM 360/91 digital computer. Focal region characteristics are plotted with the aid of a CalComp plotter. Comparison between the GSFC Huygens wavelet approach, JPL measurements, and JPL computer results based on the near field spherical wave expansion method are made wherever possible.

Schmidt, R. F.↗
NASA NTRS1981

Experiment K305: Quantitative analysis of selected bone parameters. Supplement 3A: Trabecular spacing and orientation in the long bones

Values of mean trabecular spacing computed from optical diffraction patterns of 1:1 X-ray micrographs of tibial metaphysis and those obtained by standard image digitization techniques show excellent agreement. Upper limits on values of mean trabecular orientation deduced from diffraction patterns and the images are also in excellent agreement. Values of the ratio of mean trabecular spatial density in a region of 300 micrometers distal to the downwardly directed convexity in the cartilage growth plate to the value adjacent to the plate determined for flight animals sacrificed at recovery were significantly smaller than values for vivarium control animals. No significant differences were found in proximal regions. No significant differences in mean trabecular orientation were detected. Decreased values of trabecular spatial density and of both obsteoblastic activity and trabecular cross-sectional area noted in collateral researches suggest decreased modeling activity under weightlessness.

Judy, M. M.↗