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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Multi-MHz time-of-flight electronic bandstructure imaging of graphene on Ir(111)

In the quest for detailed spectroscopic insight into the electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines the 3D detection scheme of a time-of-flight momentum microscope with an optimized filling pattern of the BESSY II storage ring. Here, comprehensive data sets covering the full surface Brillouin zone have been used to study faint substrate-film hybridization effects in the electronic structure of graphene on Ir(111), revealed by a pronounced linear dichroism in angular distribution. The method paves the way to 3D electronic bandmapping with unprecedented data recording efficiency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Nd:AlN polycrystalline ceramics: A candidate media for tunable, high energy, near IR lasers

We present processing and characterization of Nd-doped aluminum nitride (Nd:AlN) polycrystalline ceramics. We compare ceramics with significant segregation of Nd to those exhibiting minimal segregation. Spatially resolved photoluminescence maps reveal a strong correlation between homogeneous Nd doping and spatially homogeneous light emission. The spectroscopically resolved light emission lines show excellent agreement with the expected Nd electronic transitions. Notably, the lines are significantly broadened, producing near IR emission (~1077 nm) with a remarkable ~100 nm bandwidth at room temperature. We attribute the broadened lines to a combination of effects: multiple Nd-sites, anisotropy of AlN and phonon broadening. These broadened, overlapping lines in a media with excellent thermal conductivity have potential for Nd-based, tunable lasers with high average power.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

Many of water’s remarkable properties arise from its tendency to form an intricate and robust hydrogen bond network. Understanding the dynamics that govern this network is fundamental to elucidating the behavior of pure water and water in biological and physical systems. In ultrafast nonlinear infrared experiments, the accessible time scales are limited by water’s rapid vibrational relaxation (1.8 ps for dilute HOD in H 2 O), precluding interrogation of slow hydrogen bond evolution in non-bulk systems. Here in this paper, hydrogen bonding dynamics in bulk D 2 O were studied from the perspective of the much longer lived (36.2 ps) CN stretch mode of selenocyanate (SeCN-) using polarization selective pump-probe (PSPP) experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and molecular dynamics simulations. The simulations make use of the empirical frequency mapping approach, applied to SeCN - for the first time. The PSPP experiments and simulations show that the orientational correlation function decays via fast (2.0 ps) restricted angular diffusion (wobbling-in-a-cone) and complete orientational diffusive randomization (4.5 ps). Spectral diffusion, quantified in terms of the frequency-frequency correlation function, occurs on two time scales. The initial 0.6 ps time scale is attributed to small length and angle fluctuations of the hydrogen bonds between water and SeCN - . The second 1.4 ps measured time scale, identical to that for HOD in bulk D 2 O, reports on the collective reorganization of the water hydrogen bond network around the anion. Lastly, the experiments and simulations provide details of the anion-water hydrogen bonding and demonstrate that SeCN- is a reliable vibrational probe of the ultrafast spectroscopy of water.

14 SOLAR ENERGY↗
DOE OSTI2013

Lasing in the UV, IR and visible spectral ranges in a runaway-electron-preionised diffuse dischrage

Lasers on the mixtures of inert gases, H{sub 2}, D{sub 2}, and nitrogen with NF{sub 3} and (or) SF{sub 6} are studied under pumping by the volume (diffusive) discharge formed in a nonuniform electric field due to runaway-electron preionisation. Generation in the IR, visible and UV spectral ranges is obtained on atomic transitions of neon ({lambda} = 585.3 nm), argon (750.3 nm) and fluorine (712.8 and 731.1 nm), and on molecular transitions of N2 (337.1 nm), XeF * (351 and 353 nm), HF (2.8 - 3.2 {mu}m) and DF (3.8 - 4.2 {mu}m). It is shown that in N{sub 2} - SF{sub 6}, H{sub 2} - SF{sub 6} and D{sub 2} - SF{sub 6} mixtures the generation efficiency approaches the limiting values. (lasers)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Near-IR supercontinuum generation based on a telecom single-mode fibre in an all-fibre format, and its power combining

Near-IR supercontinuum (SC) is generated based on a standard telecommunication single-mode (SM) fibre in an all-fibre format. The observed spectrum covers the spectral range from 1050 nm to 1700 nm. High-efficiency combining of the SC power is demonstrated for the first time, and the spectral SC properties are shown to be maintained after power combining. The results may find applications in sensing, spectroscopy and medicine. (control of laser radiation parameters)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

On the possibility of the generation of high harmonics with photon energies greater than 10 keV upon interaction of intense mid-IR radiation with neutral gases

Based on the analytical quantum-mechanical description in the framework of the modified strong-field approximation, we have investigated high harmonic generation of mid-IR laser radiation in neutral gases taking into account the depletion of bound atomic levels of the working medium and the electron magnetic drift in a high-intensity laser field. The possibility is shown to generate high-order harmonics with photon energies greater than 10 keV under irradiation of helium atoms by intense femtosecond laser pulses with a centre wavelength of 8 – 10.6 μm. (interaction of radiation with matter)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Comparative analysis of post-focal filamentation of focused UV and IR laser pulses in air

We report the results of laboratory experiments and numerical calculations of the spatial position and structure of a plasma channel produced in air by high-power focused femtosecond laser radiation with wavelengths of 740 and 248 nm as a result of its self-focusing and filamentation. A comparative analysis of the physical patterns of filamentation of IR and UV laser beams with variations in the beam focal length, transverse size and power is performed. It is found that a plasma channel beyond the linear focal waist of the laser beam is formed differently for two different spectral ranges. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Visible supercontinuum radiation of light bullets in the femtosecond filamentation of IR pulses in fused silica

We report experimental and theoretical investigations of visible supercontinuum generation in the formation of light bullets in a filament produced by IR pulses. In the filamentation of a 1700 – 2200 nm pulse in fused silica, bright tracks are recorded resulting from the recombination glow of carriers in the laser plasma produced by a sequence of light bullets and from the scattering in silica of the visible supercontinuum generated by the light bullets. It is found that the formation of a light bullet is attended with an outburst of a certain portion of supercontinuum energy in the visible range. The energy outburst is the same for all bullets in the sequence and becomes smaller with increasing pulse wavelength. (extreme light fields and their applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Periodic colour-centre structure formed under filamentation of mid-IR femtosecond laser radiation in a LiF crystal

A colour-centre structure formed in a LiF crystal under filamentation of a femtosecond mid-IR laser pulse with a power slightly exceeding the critical power for self-focusing has been experimentally and theoretically investigated. Strictly periodic oscillations have been detected for the first time for the density of the colour centres induced in an isotropic LiF crystal under filamentation of a laser beam with a wavelength tuned in the range from 2600 to 3350 nm. The structure period is found to be about 30 μm. With an increase in the laser radiation wavelength, the period of the oscillations decreases and their amplitude increases. The maximum colour centre density, observed under filamentation of a 3100-nm beam, is related to the increased contribution of the direct generation of colour centres as a result of the absorption of an integer number of photons by the exciton band. It is numerically shown that the formation of a periodic colour-centre structure in LiF is due to the periodic change in the light field amplitude in the light bullet (1.5 optical periods long) formed under filamentation. (extreme laser radiation: physics and fundamental applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

IR luminescence of Fe{sup 2+} : ZnSe single crystals excited by an electron beam

Spectral-kinetic characteristics of the cathodoluminescence of Fe{sup 2+} : ZnSe single crystals are studied at T='300' and 80 K. These characteristics correspond to the IR luminescence spectrum and kinetics of Fe{sup 2+} ions in ZnSe crystals optically excited into the impurity absorption band. The obtained results open a real possibility of pumping Fe{sup 2+} : ZnSe lasers by hot electrons. (letters)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Superluminescent bismuth-doped fibre IR source for the range 1700−1750 nm

We have demonstrated the first superluminescent IR (1700−1750 nm) source based on bismuth-doped high-germania fibre. Its main output characteristics are as follows: centre wavelength, 1730 nm; emission bandwidth, 50 nm at an output power of ∼7 mW; optical efficiency, ∼1%. (paper)

42 ENGINEERING↗
DOE OSTI2017

Influence of induced colour centres on the frequency – angular spectrum of a light bullet of mid-IR radiation in lithium fluoride

The influence of the occurrence of a structure consisting of long-lived colour centres, formed in an LiF crystal upon filamentation of femtosecond mid-IR radiation, on the supercontinuum characteristics is investigated. With an increase in the number of incident pulses, the length and transverse size of the structure of colour centres induced in LiF increase, and the supercontinuum spectrum in the short-wavelength region is markedly transformed due to the occurrence of the waveguide propagation regime, absorption, and scattering of radiation from the newly formed structure of colour centres. Under these conditions, the intensity of the anti-Stokes wing decreases by two orders of magnitude after several tens of pulses. Spectral components arise in the visible range, the angular divergence of which increases with increasing wavelength. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

10-W mid-IR optical parametric oscillators based on ZnGeP{sub 2} elements pumped by a fibre-laser-pumped Ho: YAG Laser. Experimental and numerical study

The possibility of increasing the power and efficiency of 3.5 – 5.0 μm optical parametric oscillators (OPOs) based on one or two ZnGeP{sub 2} crystals pumped by a repetitively pulsed Ho: YAG laser ( λ = 2097 nm), which, in turn, is pumped by a thulium fibre laser ( λ = 1908 nm), is studied. The OPO based on a tandem of ZnGeP{sub 2} elements is demonstrated to generate high-quality beams with an average power up to 10 W in pulses with durations of 15 – 25 ns at a repetition rate of ∼17 kHz. The total conversion efficiency of the fibre laser power to the mid-IR radiation reached 25%. A theoretical OPO model explaining a cluster spectrum and higher output power in the case of the ZnGeP{sub 2} tandem than in the case of a single element is developed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Broadband mid-IR difference-frequency generation in 5 mol % MgO-doped periodically and aperiodically poled lithium niobate

We have theoretically investigated broadband mid-infrared (mid-IR) difference-frequency generation (DFG) in 5 mol % MgO-doped periodically poled lithium niobate (5 mol % MgO : PPLN) based on quasi-phase-matching (QPM) with group-velocity matching (GVM) between the pump and the idler for the eee interaction of QPM. The acceptance bandwidths are 282.3 nm and 35.4 nm around 3.4 μm with the signal and pump wavelengths fixed at 1.550 μm and 1.064 μm, and the required QPM periods are 30.26 μm and 30.25 μm, respectively. A method which can broaden the flattop QPM DFG acceptance bandwidth (ABW) around the GVM wavelength for the idler wavelength in 5 mol % MgO-doped aperiodically poled lithium niobate (5 mol % MgO : APPLN) is proposed. The structure of 5 mol % MgO : APPLN is optimised using a genetic algorithm by adjusting its parameters. The simulation results show that under the GVM conditions, the maximum ABW for the idler is 1045.9 nm and 96.6 nm at a fixed signal wavelength of 1.550 μm and at a fixed pump wavelength of 1.064 μm, respectively. The tradeoff between the reduced effective nonlinear coefficient and DFG ABW is discussed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Mid-IR hollow-core silica fibre Raman lasers

This paper presents a brief overview of the main designs, recent advances and future prospects in the development of mid-IR hollow-core silica fibre Raman lasers. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Similarity parameter for the process of mid-IR light bullet formation

We study the influence of the ratio of diffraction and dispersion lengths of a femtosecond mid-IR wave packet on the filamentation threshold power and the light bullet (LB) formation upon nonlinear optical interaction with solid-state dielectrics under the conditions of anomalous group velocity dispersion. It is found that the ratio of the threshold power of filamentation and LB formation to the critical power of stationary self-focusing is independent of the radiation wavelength and the medium characteristics and is determined by the similarity parameter, equal to the ratio of the diffraction length to the dispersion one. With an increase in the similarity parameter, the threshold power of filamentation and light bullet formation increases. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Mid-IR reflectance spectrum of multilayer graphene: Influence of adsorbate at the graphene – substrate interface

Water adsorbate at the interface between graphene and SiO{sub 2}/Si substrate is found to affect the reflectance spectra of (3 – 6)-layer graphene in the mid-IR range (λ = 2 – 16 μm). The sample under study was previously kept in acetone vapour to remove water adsorbate from the graphene – substrate interface. The graphene reflectance in the range of 8 – 16 μm tends to decrease with recovery of water adsorbate layer at the graphene – substrate interface at room temperature and relative air humidity RH = 40 % – 60 %. The observed effect is most likely caused by the blue shift of the absorption edge at interband transitions due to the change in the Fermi level position in the graphene valence band under the influence of the charge induced in graphene by the water adsorbate film. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Formation and optical properties of IR photoluminescence centres in bismuth-containing aluminophosphate glass

We have prepared aluminophosphate glass samples differing in bismuth oxide content and demonstrating broadband near-IR photoluminescence. Analysis of their photoluminescence spectra leads us to conclude that they contain two main types of emission centres, one of which seems to be a bismuth monocation and the other is a cluster ion. In addition to these luminescence centres, the aluminophosphate glasses contain a nonluminescent bismuth-containing centre responsible for the broad, strong optical absorption band peaking at 450 nm. (active media)

36 MATERIALS SCIENCE↗