Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “optical absorption”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Electro-physical properties of surface-barrier diodes on low-resistance n-Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 crystals

The electro-physical properties of Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 n-type conductivity single crystals with relatively low resistivity were studied. The determined resistivity of semiconductor single crystals Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 n-type conductivity is equal to ρ≈2 Ω-cm at 293K. The activation energy of dark conductivity, measured from the temperature dependence of the resistivity of the In/Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 /In structure, is equal to ΔE≈0.11eV. From optical measurements of the absorption coefficient from the energy of photons in the region of large α, the band-gap width of the single crystal was found, which is equal to E g =1.53eV. Diode structures of Ni/Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 /In obtained by vacuum sputtering of Ni on the surface of a single crystal n-Cd 0.96 Mn 0.04 Te 0.96 Se 0.04 were manufactured and studied. Here, the rectification coefficient at a voltage of U=1V is equal to 10 8 . Within the framework of the Sah-Noys-Shockley carrier generation-recombination model, a quantitative match of the experimental measurements of the volt-ampere characteristics with the calculation was achieved.

(Cd,Mn)(Te,Se)↗
DOE OSTI2025

Plasma Assisted Combustion and Chemical Processing: Chapter 9 - Plasma Diagnostics

Plasma dynamics and chemistry have a broad range of timescales from picoseconds to milliseconds. In addition, it involves nonequilibrium energy transfer between electrons, ions, electronically and vibrationally excited states, radicals, intermediate species, and reactants and products as well as surface charges and chemistry. To understand plasma physics and chemistry, it is essential to conduct time and space resolved, quantitative detection of nonequilibrium temperature distributions, electron energy and number density, electric field, and species concentrations. There are enormous publications and review articles on this subject. The focus of this chapter is to be placed on the most recent progress in gas phase plasma properties and chemistry, especially on optical emission spectroscopy, laser absorption spectroscopy, Faraday rotational spectroscopy, Raman and Thompson scattering, femtosecond and picosecond (fs/ps) coherent anti-Stokes Raman scattering (CARS) spectroscopy, and electric field-induced second harmonic generation methods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Ultrafast transient absorption measurements of photocarrier dynamics in PdSe 2

We investigate the photocarrier dynamics in bulk PdSe 2 , a layered transition metal dichalcogenide with a novel pentagonal structure and unique electronic and optical properties. Using femtosecond transient absorption microscopy, we study the behavior of photocarriers in mechanically exfoliated bulk PdSe 2 flakes at room temperature. By employing a 400 nm ultrafast laser pulse, electron–hole pairs are generated, and their dynamics are probed using an 800 nm detection pulse. Our findings reveal that the lifetime of photocarriers in bulk PdSe 2 is approximately 210 ps. Furthermore, by spatially resolving the differential reflection signal, we determine a photocarrier diffusion coefficient of about 7.3 cm 2 s –1 . Based on these results, we estimate a diffusion length of around 400 nm and a photocarrier mobility of approximately 300 cm 2 V –1 s –1 . Furthermore, these results shed light on the ultrafast optoelectronic properties of PdSe 2 , offer valuable insights into photocarriers in this emerging material, and enable design of high-performance optoelectronic devices based on PdSe 2 .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Photocarrier Dynamics in TlGaS 2 Nanoflakes and van der Waals Heterostructures with Hexagonal Boron Nitride and WS 2 Nanoflakes: Implications for Optoelectronic Applications

We present an experimental investigation on photocarrier dynamics in a TlGaS 2 bulk crystal and its heterostructures with hexagonal BN and WS 2 . The samples were obtained by mechanical exfoliation and dry transfer techniques. The photocarrier dynamics was monitored by a transient absorption technique. We observed a direct optical transition of about 555 nm in the TlGaS 2 crystal. By utilizing transient absorption of that transition, we obtained a hot-carrier energy relaxation time of less than 1 ps and a carrier lifetime of about 300 ps in TlGaS 2 at room temperature. In the hexagonal-BN-TlGaS 2 heterostructure, the photocarrier dynamics was similar to that in TlGaS 2 , indicating the type-I band alignment of this structure with both band extremes located in TlGaS 2 . In the monolayer WS 2 -TlGaS 2 heterostructure, we observed charge transfer from TlGaS 2 to WS 2 and an extended lifetime of the transferred carriers in WS 2 . Here, these results introduce TlGaS 2 as a promising layered material for developing two-dimensional van der Waals materials that can be combined with other two-dimensional materials for various optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optical Classification of Lower Amazon Waters Based on In Situ Data and Sentinel-3 Ocean and Land Color Instrument Imagery

Optical water types (OWTs) were identified from an in situ dataset of concomitant biogeochemical and optical parameters acquired in the Amazon River and its tributaries, in the Lower Amazon region, at different hydrological conditions from 2014 to 2017. A seasonal bio-optical characterization was performed. The k-means classification was applied to the in situ normalized reflectance spectra (rn(λ)), allowing the identification of four OWTs. An optical index method was also applied to the rn(λ) defining the thresholds of the OWTs. Next, level-3 Sentinel-3 Ocean and Land Color Instrument images representative of the seasonal discharge conditions were classified using the identified in situ OWTs as reference. The differences between Amazon River and clearwater tributary OWTs were dependent on the hydrological dynamics of the Amazon River, also showing a strong seasonal variability. Each OWT was associated with a specific bio-optical and biogeochemical environment assessed from the corresponding absorption coefficient values of colored dissolved organic matter (aCDOM) and particulate matter (ap), chlorophyll-a and suspended particulate matter (SPM) concentrations, and aCDOM/ap ratio. The rising water season presented a unique OWT with high SPM concentration and high relative contribution of ap to total absorption compared to the other OWTs. This bio-optical characterization of Lower Amazon River waters represents a first step for developing remote sensing inversion models adjusted to the optical complexity of this region.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Ultrafast vertical photoconductive intrinsic diamond switch with high current (17.1 A at 1 kV)

Here, this Letter reports on a vertical, bulk-conducting photoconductive semiconductor switch (PCSS) fabricated on an intrinsic Type IIa single-crystal diamond substrate. Under near-bandgap excitation at 225 nm with a 20 μ J pulse, a strong photocurrent response of 17.1 A at 1 kV DC bias magnitude is obtained by (i) tuning the optical trigger wavelength to the “matched-absorption” window (224–235 nm) near the band edge, where the optical penetration depth becomes comparable to the 500 μ m substrate thickness, and (ii) choosing the bias polarity ensuring electron-dominant conduction, given that electrons have a higher mobility than holes in diamond. The PCSS has an area-normalized responsivity of 54.2 mA W −1 cm −2 and an effective on-resistance of 8.48 Ω, with a fast 90%–10% transient fall time of 25 ns, attributed to carrier sweep-out. These results support vertical, bulk-conducting intrinsic diamond PCSS as a promising platform for high-power optical switching and provide new insight into intrinsic photoconductivity in diamond.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Assessing the link between aerosol mixing state, structure and composition and their optical properties: Ascension Island as a testbed for the South‐East Atlantic aerosol regimes

Forest and savanna fires are a major source of pollution over the globe. Such fire events emit to the atmosphere a considerable amount of “fluffy” fractal black looking particles that are often referred to as black carbon (BC) or soot aerosols. In fact, BC particles (aerosols) emitted from savanna and agricultural fires over the African continent play an important role in the region’s and the global climate. These fires occur each year between July and October, which is referred to as the biomass burning (BB) season and are considered among the globe's largest man-made emission sources of BC particles. However, during these fire events, not only BC particles are emitted, but also other types of particles and gases that can interact with each other to create new particles, generating a slew of particles often generally referred to as BB aerosols. Although the majority of the fire emissions occur inland in the sub-Saharan part of Africa, their effect reaches far beyond the continent due to the prevailing easterly winds, which transport those aerosols over the South-East Atlantic (SEA) ocean, off the west-coast of Africa. The reason why these particles are so important to the regional and global climate is that they absorb sunlight radiation, which overall warms the climate. However, the magnitude of this warming effect is highly uncertain and depends upon a multitude of aspects. Our overarching goal for this project was to better understand the changes in the aerosol properties as they transport from fire sources downstream toward the ocean and how this can eventually affect the earth's radiative budget in terms of warming or cooling. Following the above, our work here was focused on the investigation of the African BB aerosol plumes mixing state (mixing of BB aerosols and other aerosol types), composition and size distribution as they transport from the African continent towards the SEA ocean, and their link with some of the commonly measurable bulk optical properties such as mass absorption coefficient (MAC) and single scattering albedo (SSA). We utilized three field missions that were conducted over the SEA ocean between 2016 and 2018. Specifically, we used (1) ground-based measurements from the DOE ARM Mobile Facility (AMF1), which was deployed at Ascension Island (ASI) for the LASIC (Layered Atlantic Smoke Interactions with Clouds) campaign between June 2016 and October 2017, (2) airborne measurements from the UK CLARIFY (Clouds and Aerosol Radiative impacts and Forcing) campaign during Aug-Sep-2017, and (3) airborne measurements from the ORACLES (Observations of Aerosols above Clouds and their interactions) campaign during Aug-2017, and Sep-Oct-2018. The three campaigns cover a relatively large region, from the western African coast on the east towards Ascension Island in the middle of the SEA to the west. We used the data gathered by these campaigns to find how BB properties and composition change from near emission sources (the ORACLES campaign flights) downstream (the CLARIFY flights and the ground based LASIC measurements). We used particle trajectory following methodologies to connect the measurements from the different campaigns, which allowed us to follow a certain aerosol plume (airmass) from near-source towards Ascension Island. We found out that atmospheric aging processes governed by the UV light from the sun (photochemistry) and cloud processes (aqueous chemistry) govern the changes seen in the particle composition during the transport were more dominant in dictating aerosol composition than specific emission composition or source types. We assessed how aerosol optical properties change during the BB season and what are the main drivers of this change. We found that the enhanced ratio of BC to CO is well correlated with single scattering albedo (SSA) and mass absorption coefficient (MACBC), providing a simple way to estimate the aerosol optical characteristics in the south-eastern Atlantic Ocean. From the analysis of the location of BB, the primary source fuel, the water content in the fuel, combined with the mean cloud cover and precipitation in the transport areas of the BB plume, we conclude that the increase in BC/CO from June to August is likely to be caused by burning becoming more flaming (hot fires), and the decrease in BC/CO in September and October may be caused by smoldering (colder) fires. We found that aerosol hygroscopicity increases with decreasing altitude below 2km, and that enhanced BB hygroscopicity at lower altitudes is mainly due to a lower organic aerosol (OA) fraction, increased sulfate fraction, and greater hygroscopicity parameter of OA at lower altitudes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Linear response of molecular polaritons

In this article, we show that the collective light–matter strong coupling regime where N molecular emitters couple to the photon mode of an optical cavity can be mapped to a quantum impurity model where the photon is the impurity that is coupled to a bath of anharmonic transitions. In the thermodynamic limit where N ≫ 1, we argue that the bath can be replaced with an effective harmonic bath, leading to a dramatic simplification of the problem into one of the coupled harmonic oscillators. We derive simple analytical expressions for linear optical spectra (transmission, reflection, and absorption) where the only molecular input required is the molecular linear susceptibility. This formalism is applied to a series of illustrative examples, showing the role of temperature, disorder, vibronic coupling, and optical saturation of the molecular ensemble, explaining that it is useful even when describing an important class of nonlinear optical experiments. For completeness, we provide Appendixes A–C that include a self-contained derivation of the relevant spectroscopic observables for arbitrary anharmonic systems (for both large and small N) within the rotating-wave approximation. While some of the presented results herein have already been reported in the literature, we provide a unified presentation of the results as well as new interpretations that connect powerful concepts in open quantum systems and linear response theory with molecular polaritonics.

Chemistry↗
DOE OSTI2025

Online monitoring of lanthanide species with combined spectroscopy in flowing aqueous aerosol systems

Combined spectroscopic analysis through absorption and laser-induced breakdown spectroscopy (LIBS) was used to monitor Nd and Pr concentrations in a flowing aqueous system. A unique, online sampling approach was employed that allowed for an approximately closed analysis loop of liquids from a reservoir. Absorption spectroscopy was performed with an optical flow cell, and LIBS was performed on an aerosol stream. Multivariate calibrations based on combined absorption and LIBS signals were built for Nd and Pr and then used to monitor concentrations in mixed solutions in a series of spiking tests. In these tests, the concentrations of Nd and Pr in solution were intermittently changed while spectroscopic signals were monitored in real-time. The combined spectroscopic signals and multivariate models were successful in monitoring changing concentrations of lanthanide species with high accuracy and minimal latency. Root-mean squared error of predictions were 0.015 mol L −1 and 0.019 mol L −1 for Nd and Pr respectively, and these lanthanides were able to be monitored to an accuracy of < 0.2 wt%. This work demonstrates both the capabilities of a sampling system for online analysis of liquids and the capabilities of multimodal spectroscopic characterization for real-time, continuous tracking of species in potentially hazardous liquid systems.

absorbance spectroscopy↗
DOE OSTI2024

"Soiling, Cleaning, and Abrasion: The Results of the Five-Year Photovoltaic Glass Coating Field Study" [Slides]

External contamination ("soiling") of the incident surface is a major limiting factor for solar technologies. A 5-year field glass coupon study was conducted to better understand external contamination and its effects; compare cleaning methods and the use of preventative coatings; and explore the abrasion resulting from cleaning to advise on accelerated abrasion testing. Test sites included the cities of Dubai (UAE), Kuwait City (Kuwait), Mesa (AZ), Mumbai (India), and Sacramento (CA). Through the 5-year cumulative study, dry brush, water spray, and wet sponge and squeegee cleaning methods were compared to no cleaning. Optical microscopy was used to obtain images, including representative color images, grayscale images for object analysis, and oblique images for coating integrity assessment. A thresholding protocol was developed to analyze and distinguish specimens using the ImageJ software. Optical performance was quantified using a spectrophotometer, including comprehensive optical characterization (transmittance, reflectance, and absorptance in addition to forward- and back-scattering). Atomic force microscopy was used to verify the abrasion damage morphology, including the width and depth of surface scratches. Analysis of the results included correlation of optical performance and particle area coverage, rank order (by coating or location), and the acceleration factor for abrasion damage. The efficacy of external cleaning was more readily distinguished from the effectiveness of antisoiling coatings. The acceleration factor for dry brush cleaning of a porous silica coating was found to be on the order of unity.

14 SOLAR ENERGY↗
DOE OSTI2022

Gamma-radiation-induced negative nonlinear absorption in quartz glass

The effect of ionizing radiation on the nonlinear optical properties of materials needs to be considered for applications that employ high-power laser pulses in extreme radiation environments. The Heraeus Infrasil302 optical quartz glass was irradiated by gamma rays, and its nonlinear absorption was measured using the open-aperture Z-scan technique with nanosecond laser pulses. Irradiation results in a negative nonlinear absorption coefficient whose magnitude increases with irradiation dose. Nonlinear absorption coefficients of -0.78, -1.14, -1.29, and -1.88~ × ~10 -13 m/W are measured for gamma doses of 600 krad, 1.2 Mrad, 3.6 Mrad, and 10 Mrad, respectively. Thermal annealing restores the optical properties of quartz-glass to their unirradiated values. It is suggested that metallic impurities introduced by the manufacturing process have a role in inducing saturated absorption in irradiated quartz glass, which manifests as negative nonlinear absorption coefficient, and is demonstrated by comparing Infrasil302 quartz results to equivalent irradiated measurements for Spectrosil2000 quartz.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Realization of a wide steering end-fire facet optical phased array using silicon rich silicon nitride

The design, fabrication, and characterization of a 16-element optical phased array (OPA) using a high index (n = 3.1) silicon-rich silicon nitride (SRN) is demonstrated. Here, we present one-dimensional beam steering with end-fire facet antennas over a wide steering range of >115° at a fixed wavelength of 1525 nm. A beam width of 6.3° has been measured at boresight, consistent with theory. We demonstrate SRN as a viable material choice for chip-scale OPA applications due to its high thermo-optic coefficient, high optical power handling capacity [negligible two-photon absorption (TPA)], wide transparency window, and CMOS compatibility.

Nejadriahi, Hani↗
DOE OSTI2022

Elimination of remnant phases in low-temperature growth of wurtzite ScAlN by molecular-beam epitaxy

We report growth of wurtzite Sc x Al 1-x N (x < 0.23) by plasma-assisted molecular-beam epitaxy on c-plane GaN at high temperatures significantly alters the extracted lattice constants of the material due to defects likely associated with remnant phases. In contrast, ScAlN grown below a composition-dependent threshold temperature exhibits uniform alloy distribution, reduced defect density, and atomic-step surface morphology. The c-plane lattice constant of this low-temperature ScAlN varies with composition as expected from previous theoretical calculations and can be used to reliably estimate alloy composition. Moreover, lattice-matched Sc 0.18 Al0 .82 N/GaN multi-quantum wells grown under these conditions display strong and narrow near-infrared intersubband absorption lines that confirm advantageous optical and electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamical Control of Broadband Coherent Absorption in ENZ Films

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Visualization of Thermal and Strain Dynamics in X-ray Optics by Time-Resolved Rocking Curve Imaging

The absorption of intense X-ray pulses from free-electron lasers by X-ray crystal optics triggers rapid thermal and mechanical responses, including lattice compression, expan- sion, and strain-wave propagation, which dynamically modify diffraction conditions and wavefront properties. These effects pose significant challenges for next-generation high- repetition-rate X-ray sources, particularly for crystal monochromators used in XFEL beam- lines and self-seeding. Here, we demonstrate time-resolved rocking curve imaging (TrRCI) of X-ray Bragg optics with high spatial resolution (6.4 μm) and sub-1-μrad angular resolu- tion, enabling direct visualization of lattice dynamics from nanoseconds to microseconds. By combining a high-flux beamline at SPring-8, a scintillator-coupled sCMOS detector, and a synchronized femtosecond laser system, we capture lattice dynamics induced by tran- sient laser heating with a strain sensitivity on the order of 10−6 . Our results reveal transient lattice deformation and the propagation of laser-induced strain waves over millimeter-scale distances. This approach provides experimental benchmarks for understanding heat-load effects in high-repetition-rate X-ray optics.

Source record↗
DOE OSTI2023

Spin–orbit effects on the electronic and optical properties of lead iodide

Lead iodide (PbI2) has gained much interest due to its direct electronic gap in the visible range and layered crystal structure. It has thereby been considered as a promising material for applications in atomically thin optoelectronic devices. In this work, we present a detailed investigation of the effect of spin–orbit coupling (SOC) that arises from the presence of heavy atoms on the electronic and optical properties of PbI2 using first-principles calculations based on density-functional theory and many-body perturbation theory. We find that SOC not only alters the bandgap but also induces the mixing of orbital characters, resulting in a significant change in the overall band structure and charge carrier effective masses. Moreover, the band orbital mixing caused by SOC results in the dramatic change in optical transition matrix elements and, correspondingly, the absorption spectrum. Our experimentally measured absorption spectra validate the calculation results and demonstrate the importance of SOC in the optical processes of PbI2. Our findings provide insights that are important for the potential use of PbI2 as a material platform for visible optoelectronic devices.

Physics↗