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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Reflection-Absorption Infrared Spectroscopy of Thin Films Using an External Cavity Quantum Cascade Laser

We present experimental demonstrations using a broadly tunable external cavity quantum cascade laser (ECQCL) to perform Reflection-Absorption InfraRed Spectroscopy (RAIRS) of thin layers and residues on surfaces. The ECQCL compliance voltage was used to measure fluctuations in the ECQCL output power and improve the performance of the RAIRS measurements. Absorption spectra from self-assembled monolayers of a fluorinated alkane thiol and a thiol carboxylic acid were measured and compared with FTIR measurements. RAIRS spectra of the explosive compounds PETN, RDX, and tetryl deposited on gold substrates were also measured. Rapid measurement times and low noise were demonstrated, with < 1E-3 absorbance noise for a 10 second measurement time.

Infrared Spectroscopy↗
DOE OSTI2022

Using spectroscopic ellipsometry and single-angle reflectance to derive accurate optical constants for chemical forms of aspartame

Variable angle spectroscopic ellipsometry and single-angle infrared reflectance methods have been used to derive the complex optical constants n and k in the mid-infrared spectral region for aspartame. Aspartame exists in four unique forms – three of which incorporate water into the lattice, as well as the anhydrate form. The different forms can induce splitting or slight wavenumber shifts in the spectral features. Pressed pellets of neat powder were prepared and measured using both methods to derive the optical constants. Different n and k values were obtained depending on the percentage of the forms of aspartame, which was determined using powder X-ray diffraction (XRD) analysis.

optical constants, refractive index, extinction co↗
DOE OSTI2018

Determining the Size of Pores in a Partially Transparent Ceramics from Total-Reflection Spectra

A technique is proposed for determining the pore-size distribution based on measuring the dependence of total reflectance in the domain of partial transparency of a material. An assumption about equality of scattering-coefficient spectra determined by solving the inverse radiation transfer problem and by theoretical calculation with the Mie theory is used. The technique is applied to studying a quartz ceramics. The poresize distribution is also determined using mercury and gas porosimetry. All three methods are shown to produce close results for pores with diameters of <180 nm, which occupy ~90% of the void volume. In the domain of pore dimensions of >180 nm, the methods show differences that might be related to both specific procedural features and the structural properties of ceramics. The spectral-scattering method has a number of advantages over traditional porosimetry, and it can be viewed as a routine industrial technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Andreev bound states. Some quasiclassical reflections

We discuss a very simple and essentially exactly solvable model problem which illustrates some nice features of Andreev bound states, namely, the trapping of a single Bogoliubov quasiparticle in a neutral s-wave BCS superfluid by a wide and shallow Zeeman trap. In the quasiclassical limit, the ground state is a doublet with a splitting which is proportional to the exponentially small amplitude for “normal” reflection by the edges of the trap. We comment briefly on a prima facie paradox concerning the continuity equation and conjecture a resolution to it.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Reflection of a probe pulse and thermal emission of electrons produced by an aluminum film heated by a femtosecond laser pulse

It is shown that an experimental decrease in the reflection of a probe femtosecond pulse from an aluminum film heated by a higher-power femtosecond pulse can be quantitatively described taking into account the inhomogeneous distribution of the laser pulse field in the film and the evolution of the electron and lattice temperature during absorption of the heating inhomogeneous field. Analysis of the electron temperature evolution on the heated film surface combined with modern concepts about the influence of a surface volume charge on thermal emission gave the relation between the amount of emitted electrons and experimental data on the heating of the aluminum film by the femtosecond pulse.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Selective reflection of laser radiation from submicron layers of Rb and Cs atomic vapors: Applications in atomic spectroscopy

We studied selective reflection (SR) of laser radiation from a window of a nanocell with thickness L ~ λ{sub 1,2}/2 filled with Rb and Cs atoms, where λ{sub 1} = 780 nm and λ{sub 2} = 852 nm are the wavelengths resonant with the D{sub 2} laser lines for Rb and Cs, respectively. It is demonstrated that the negative derivative of the SR signal profile for L > λ/2 changes to the positive one for L < λ/2. It is shown that the real-time formation of the SR signal profile derivative (SRD) with the spectral width 30–40 MHz and located at the atomic transition is, in particular, a convenient frequency marker of D{sub 2} transitions in Rb and Cs. The amplitudes of SRD signals are proportional to the atomic transition probabilities. A comparison with the known saturated absorption (SA) method demonstrated a number of advantages, such as the absence of cross-over resonances in the SRD spectrum, the simplicity of realization, a low required power, etc. An SRD frequency marker also operates in the presence of the Ne buffer gas at a pressure of 6 Torr, which allowed us to determine the Ne–Rb collisional broadening, whereas the SA method is already inapplicable at buffer gas pressures above 0.1 Torr. The realization simplicity makes the SRD method a convenient tool for atomic spectroscopy. Our theoretical model well describes the SRD signal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Selective Reflection of Potassium Vapor Nanolayers in a Magnetic Field

The selective reflection of laser radiation from the interface between a dielectric window and the atomic vapors confined in a nanocell of thickness L ≈ 350 nm is used to develop effective Doppler-broadening- free spectroscopy of potassium atoms. A small atomic line width and a relation between the signal intensity and the transition probability allowed us to resolve four lines of atomic transitions responsible for the D1 lines of the {sup 39}K and {sup 41}K isotopes. Two groups containing four atomic transitions form in an applied magnetic field upon pumping by radiation with circular polarization σ{sup +} or σ{sup –}. Different intensities (probabilities) of transitions for the σ{sup +} and σ{sup –} excitations are detected in magnetic field B{sub 0} ≈ A{sub hfs}/μ{sub B} ≈ 165 G (A{sub hfs} is the magnetic dipole constant for the ground state and μ{sub B} is the Bohr magneton). A substantially different situation is observed at B ≫ B{sub 0}, since high symmetry appears for the two groups formed by radiation with circular polarization σ{sup +} or σ{sup –}. Each group is the mirror image of the other group with respect to the frequency of the 4{sup 2}S{sub 1/2}–4{sup 2}P{sub 1/2} transition, which additionally proves the occurrence of the complete Paschen–Back regime of the hyperfine structure at B ≈ 2.5 kG. A developed theoretical model well reproduces the experimental results. Possible practical applications are described. The results obtained can also be applied to the D{sub 1} lines of {sup 87}Rb and {sup 23}Na.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Masking of a High-Reflectivity Sphere by a Layer with a Random Quasi-Zero Refractive Index

The method of masking of a large-radius sphere made of an arbitrary material by a masking coating with a random quasi-zero refractive index is substantiated theoretically and experimentally. In this method of masking, the sphere is first coated with a mirror layer (e.g., high-reflectivity silver) and then with a masking layer with a thickness much smaller than the radius of the sphere. The fraction of the external radiation intensity bending around the sphere at the points of observation near the surface of the sphere and the extinction cross section of the sphere with the masking coating for points of observation far away from the sphere are calculated. It is shown that extinction cross section Q of the sphere with a masking coating is much smaller than 2D, where D is the geometrical cross section of the sphere; this corresponds to the masking effect for the sphere in the wavelength range of at least 450–1200 nm in the transparency region of the masking coating.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Peculiarities in Transmission (Reflection) of Ultrashort Resonant Laser Pulses by a Thin Semiconductor Film in the Conditions of Exciton and Biexciton Excitation

We have studied the nonstationary transmission of two ultrashort laser pulses incident on a thin film. The radiation frequency of one of these pulses is in resonance with the two-photon transition from the ground state of the crystal to the biexciton state, while the other pulse coherently mixes the exciton and biexciton states, leading to strong renormalization of the energy spectrum of the crystal. We have obtained a system of nonlinear equations describing the time evolution of the exciton and biexciton amplitudes and the fields of three pulses transmitted through the film. We have analyzed the effect of amplitudes and widths of incident pulsed and of the time delay between them on the peculiarities of film transmission of these pulses. We have predicted the effect of a substantial time delay in the generation of the pulse transmitted through the film relative to the incident pulse, which is in resonance with the exciton–biexciton transition frequency. The possibility of generation of a precursor, viz., a pulse transmitted through the film sooner than the peak of the incident pulse reaches the film, as well as possibility of generation of a reflected pulse in the absence of the incident pulse, has been proven.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Study of photomodulated reflectance in 6H-SiC single crystals

The effect of ultraviolet irradiation of the surface of silicon-carbide (6H-SiC) single crystals on their optical reflectivity in the visible and violet spectral regions is studied. It is shown that the photoreflection-signal intensity is maximal, if the light beam is incident at the Brewster angle and polarized parallel to the plane of incidence. The relative change induced in the refractive index of the surface layers of a crystal (10{sup -3}) upon exposure to nitrogen laser radiation, caused by the generation of nonequilibrium free charge carriers in the conduction band of the material, is established.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Excitation of plasmonic terahertz photovoltaic effects in a periodic two-dimensional electron system by the attenuated total reflection method

The problem of the rectification of terahertz radiation due to plasmonic nonlinearities in a periodic two-dimensional electron system upon the excitation of plasma oscillations by the attenuated total reflection method is solved. This model allows the independent study of different plasmonic rectification mechanisms, i.e., plasmonic electron drag and plasmonic ratchet effects.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Determination of the Free Charge Carrier Concentration in Boron-Doped Silicon Nanowires Using Attenuated Total Reflection Infrared Spectroscopy

Attenuated total reflection infrared spectroscopy is used to determine the free charge carrier concentration in arrays of silicon nanowires with characteristic transverse sizes of 50–100 nm and a length of the order of 10 μm formed on lightly doped crystalline p-type silicon by metal-assisted chemical etching and subjected to the additional thermal-diffusion doping of boron at temperatures of 850–1000°C. It is found that the free hole concentration in arrays varies from 5 × 10{sup 18} to 3 × 10{sup 19} cm{sup –3} depending on the annealing temperature and is maximal at temperatures of 900–950°C. These results can be used to extend the range of potential application of silicon nanowires in photonics, sensorics, and thermoelectric power converters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Determination of Plasma Oscillations in Metals Using Total External Reflection of X-Rays

A method to determine plasma oscillations in metals with the aid of total external reflection (TER) of X-rays is proposed. It is shown that the plasmon energy, concentration of conduction electrons, and Fermi energies can be calculated using experimentally measured grazing angles of X-rays after TER. Such characteristics depend on crystallographic directions and may depend on the TER depth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Plasma Reflection in Multigrain Layers of Narrow-Bandgap Semiconductors

Qualitatively similar spectral characteristics of plasma-resonance reflection in the region of 15–25 μm were obtained for layers of electrodeposited submicron particles of InSb, InAs, and GaAs and plates of these semiconductors ground with M1-grade diamond powder. The most narrow-bandgap semiconductor InSb (intrinsic absorption edge ∼7 μm) is characterized by an absorption band at 2.1–2.3 μm, which is interpreted in terms of the model of optical excitation of electrons coupled by the Coulomb interaction. The spectra of a multigrain layer of chemically deposited PbS nanoparticles (50–70 nm) exhibited absorption maxima at 7, 10, and 17 μm, which can be explained by electron transitions obeying the energy-quantization rules for quantum dots.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Point-contact Andreev reflection spectroscopy on Bi 2 Se 3 single crystals

In order to study how Andreev reflection (AR) occurs between a superconductor and a three-dimensional topological insulator (TI), we use superconducting Nb tips to perform point-contact AR spectroscopy at 4.2 K on as-grown single crystals of Bi 2 Se 3 . Scanning tunneling spectroscopy and scanning tunneling microscopy are also used to characterize the superconducting tip and both the doping level and surface condition of the TI sample. Furthermore, the point-contact measurements show clear spectral signatures of AR, as well as a depression of zero-bias conductance with decreasing junction impedance. The latter observation can be attributed to interfacial Rashba spin-orbit coupling, and the presence of bulk bands at the Fermi level in our samples suggests that bulk states of Bi2Se3 are involved in the observed AR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

UAS remote sensing (AltaX platform): Red-green-blue (RGB) imagery, thermal infrared (TIR) imagery, and canopy reflectance (Level 0 data), Seward Peninsula, Alaska, 2023

Airborne remote sensing data collected using Brookhaven National Laboratory’s (BNL) heavy-lift unoccupied aerial system (UAS) AltaX platform on the Seward Peninsula, Alaska, USA. This package includes raw (L0) data from 11 flights flown over the NGEE-Arctic Kougarok mile marker 64 (MM64) and Teller MM 27 sites in July, 2023. The AltaX is a multi-sensor UAS platform that simultaneously measures very high spatial resolution optical red/green/blue (RGB) and thermal infrared (TIR) surface “skin” temperature imagery, as well as near-surface surface reflectance at 1 nm intervals in the visible to near-infrared spectral range from ~350 – 1000 nm. This package provides the Level 0 (raw, unprocessed) data collected by the platform and sensors. Ancillary aircraft data, flight mission parameters, and general flight conditions provided by the onboard flight and data collection computers are also included. Data and metadata are provided as text (*.txt, *.json), binary (*.dat, *.ulg), tabular (*.csv), geospatial (*.kml. *kmz), image (*.jpg, *.png, *.tif) and pdf formats. The metadata documents contain flight campaign, platform, sensor, flight and file metadata, along with a description of the L0 data and the file naming scheme.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a 15-year research effort (2012-2027) to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗