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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of absorbing coating on ablation of diamond by IR laser pulses

We study the possibility of increasing the efficiency and quality of laser ablation microprocessing of diamond by preliminary forming an absorbing layer on its surface. The laser pulses having a duration of 1 ps and 10 ns at a wavelength of 1030 nm irradiate the polycrystalline diamond surface coated by a thin layer of titanium or graphite. We analyse the dynamics of the growth of the crater depth as a function of the number of pulses and the change in optical transmission of the ablated surface. It is found that under irradiation by picosecond pulses the preliminary graphitisation allows one to avoid the laser-induced damage of the internal diamond volume until the appearance of a self-maintained graphitised layer. The absorbing coating (both graphite and titanium) much stronger affects ablation by nanosecond pulses, since it reduces the ablation threshold by more than an order of magnitude and allows full elimination of a laser-induced damage of deep regions of diamond and uncontrolled explosive ablation in the near-surface layer. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Path length and spectrum of single-cycle mid-IR light bullets in transparent dielectrics

Filamentation of femtosecond laser radiation with a wavelength of 800 – 3900 nm and a power slightly exceeding the critical self-focusing power is studied using the spectral method and the method of laser coloration in LiF crystal. It is found that the length of a filament formed in the single-pulse regime increases with increasing excitation wavelength from a few tens of micrometres at 80 nm to hundreds of micrometres at 3900 nm. In the spectral region of anomalous group velocity dispersion, starting from 2600 nm, the initially smooth luminescence profile of the long-lived induced colour centres acquires a periodic structure, demonstrating the formation of a light bullet with a duration of about one cycle of the light field oscillation and a diameter smaller than 10 μm. The path length of such bullets does not exceed 0.5 mm in the single-pulse regime and 2.7 mm in the waveguide regime. A consequence of periodic modulation of the bullet light field in the process of propagation, observed experimentally and confirmed by calculations, is the appearance of sidebands near the excitation wavelength, as well as the appearance of visible spectral components in the supercontinuum radiation, whose angular divergence increases with increasing wavelength. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Broadband mid-IR source based on a MgO : PPLN optical parametric oscillator

We have designed and tested a broadband fan-out PPLN-based optical parametric oscillator (OPO) pumped by a Q-switched Nd:YAG laser (1.064 μm) and operating in the spectral range 2.6 – 4.2 μm. The optical scheme of the OPO utilises a cylindrical pump beam expander for increasing the effective aperture of the PPLN structure and obtaining broadband generation. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Planar multifrequency mid-IR microwave-pumped lasers

The characteristics of planar repetitively pulsed diffusion-cooled HF, DF, HF – DF, Xe, and HF – DF – Xe(Kr) lasers pumped by a microwave discharge (2.45 GHz) are studied depending on the pump pulse duration (10 – 40 μs) and repletion rate (50 – 400 Hz), as well as on the composition and pressure of the working gas mixture (30 – 200 Torr) at low (to 0.6 L s{sup −1}) gas flow rates. It is demonstrated for the first time that a HF – DF – Xe gas-discharge laser may simultaneously operate as a HF – DF chemical molecular laser and a recombination laser based on xenon atom transitions and generate broadband (octave) radiation in the range 2.0 – 4.2 μm with an average output power of 43 mW and an efficiency of 0.9 %. With substitution of xenon for krypton, lasing in a HF – DF – Kr laser is obtained at wavelengths of 2.52 – 4.15 μm. Lasing in a HF – DF laser was achieved simultaneously in two spectral regions (2.7 – 2.9 and 3.6 – 4.2 μm) with an output power of ∼50 mW. It is found that a decrease in the pump pulse duration with a simultaneous increase in the pulse repletion rate for retaining the average energy deposition leads to an increase in the average output power and efficiency of the laser. At low pulse repetition rates (50 – 100 Hz) and a low gas mixture flow rate, helium buffer gas can be effectively substituted for neon. Operation of the Xe laser was achieved in the spectral range 2.03 – 3.65 μm with an average output power of 580 Mw at a pump pulse duration of 20 μs, a pulse repetition rate to 10 kHz, and a maximum efficiency of 55 %. The obtained experimental results demonstrate the possibility of creating broadband HF – DF – Xe lasers emitting in the frequency range 2 – 4 μm with a desired ratio of intensities in different spectral ranges. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Structural phase transition and manifestation of eddy currents in IR reflection spectra of PbSnTe semiconductor films

Infrared reflection spectra of thin (∼60 nm) Pb{sub 1−x} Sn{sub x}Te (x = 0.25, 0.53, 0.59) films grown by molecular beam epitaxy on GaAs/CdTe hybrid substrates have been measured at frequencies from 20 to 5500 cm{sup −1} and temperatures from 5 to 300 K. The spectra have been used to determine temperature-dependent transverse phonon and plasmon frequencies in the films, which has made it possible to identify a structural phase transition at T{sub C} ≈ 50 K. The plasma frequency of the films has been shown to increase with decreasing band gap on cooling from 300 to 77 K. The increase in plasma frequency is mainly attributable to the increase in carrier concentration and a transition of the carriers from vortex states on the film surface to the valence band. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Laser-induced transient magnons in Sr 3 Ir 2 O 7 throughout the Brillouin zone

Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic X-ray scattering we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in gapped antiferromagnets and that they persist for several picoseconds, which is opposite to what is observed in nearly gapless magnets. Overall, our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Equation of state for Hf, Ta, W, Re, Os, Ir, Pt, and Au to multi-terapascal pressures from density-functional theory

We present the zero-temperature equation of state (pressure dependence of compression) and phase stability predictions for the 5d-transition metals obtained from all-electron density-functional theory (DFT) calculations. The results compare favorably with experiments but extend beyond current experimental capabilities to 10 TPa. Our study reveals phase changes that are explained from the calculated electronic structure. The cubic face-centered and body-centered structures (fcc and bcc), together with two-, three-, and four-layered hexagonal structures, play major roles under compression. The results’ dependence on the electron exchange and correlation in the DFT approach is investigated, and it is shown that the impact of the choice, while significant at lower pressures, diminishes in the terapascal regime. We further illustrate that the normal parabolic trends in atomic volume and bulk modulus with atomic number, due to the occupation of bonding and anti-bonding 5d states, break down at TPa pressures, suggesting drastically different chemical bonding at these extreme conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Andromeda (M31) optical and infrared disk survey. I. Insights in wide-field near-IR surface photometry

We present wide-field near-infrared J and K{sub s} images of the Andromeda Galaxy (M31) taken with WIRCam at the Canada-France-Hawaii Telescope as part of the Andromeda Optical and Infrared Disk Survey. This data set allows simultaneous observations of resolved stars and near-infrared (NIR) surface brightness across M31's entire bulge and disk (within R = 22 kpc), permitting a direct test of the stellar composition of near-infrared light in a nearby galaxy. Here we develop NIR observation and reduction methods to recover a uniform surface brightness map across the 3° × 1° disk of M31 with 27 WIRCam fields. Two sky-target nodding strategies are tested, and we find that strictly minimizing sky sampling latency cannot improve background subtraction accuracy to better than 2% of the background level due to spatio-temporal variations in the NIR skyglow. We fully describe our WIRCam reduction pipeline and advocate using flats built from night-sky images over a single night, rather than dome flats that do not capture the WIRCam illumination field. Contamination from scattered light and thermal background in sky flats has a negligible effect on the surface brightness shape compared to the stochastic differences in background shape between sky and galaxy disk fields, which are ∼0.3% of the background level. The most dramatic calibration step is the introduction of scalar sky offsets to each image that optimizes surface brightness continuity. Sky offsets reduce the mean surface brightness difference between observation blocks from 1% to <0.1% of the background level, though the absolute background level remains statistically uncertain to 0.15% of the background level. We present our WIRCam reduction pipeline and performance analysis to give specific recommendations for the improvement of NIR wide-field imaging methods.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Near-IR polarized scattered light imagery of the DoAr 28 transitional disk

We present the first spatially resolved polarized scattered light H-band detection of the DoAr 28 transitional disk. Our two epochs of imagery detect the scattered light disk from our effective inner working angle of 0.″10 (13 AU) out to 0.″50 (65 AU). This inner working angle is interior to the location of the system’s gap inferred by previous studies using spectral energy distribution modeling (15 AU). We detected a candidate point source companion 1.″08 northwest of the system; however, our second epoch of imagery strongly suggests that this object is a background star. We constructed a grid of Monte Carlo Radiative Transfer models of the system, and our best fit models utilize a modestly inclined (50°), 0.01 M{sub ⊙} disk that has a partially depleted inner gap from the dust sublimation radius out to ∼8 AU. Subtracting this best fit, axi-symmetric model from our polarized intensity data reveals evidence for two small asymmetries in the disk, which could be attributable to a variety of mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

HYDROGEN PERMITTED LINES IN THE FIRST NEAR-IR SPECTRA OF Th 28 MICROJET: ACCRETION OR EJECTION TRACERS?

We report the first near-infrared detection of the bipolar microjet from T Tauri star ThA 15-28 (hereafter Th 28). Spectra were obtained with Very Large Telescope (VLT)/ISAAC for the slit both perpendicular and parallel to the flow to examine jet kinematics and gas physics within the first arcsecond from the star. The jet was successfully detected in both molecular and atomic lines. The H{sub 2} component was found to be entirely blueshifted around the base of the bipolar jet. It shows that only the blue lobe is emitting in H{sub 2} while light is scattered in the direction of the red lobe, highlighting an asymmetric extinction and/or excitation between the two lobes. Consistent with this view, the red lobe is brighter in all atomic lines. Interestingly, the jet was detected not only in [Fe II], but also in Br{gamma} and Pa{beta} lines. Though considered tracers mainly of accretion, we find that these high excitation hydrogen permitted lines trace the jet as far as 150 AU from the star. This is confirmed in a number of ways: the presence of the [Fe II] 2.13 {mu}m line which is of similarly high excitation; H I velocities which match the jet [Fe II] velocities in both the blue and red lobe; and high electron density close to the source of >6 x 10{sup 4} cm{sup -3} derived from the [Fe II] 1.64, 1.60 {mu}m ratio. These near-infrared data complement Hubble Space Telescope Imaging Spectrograph (HST/STIS) optical and near-ultraviolet data for the same target which were used in a jet rotation study, although no rotation signature could be identified here due to insufficient angular resolution. The unpublished HST/STIS H{alpha} emission is included here alongside the other H I lines. Identifying Br{gamma} and Pa{beta} as tracers of ejection is significant because of the importance of finding strong near-infrared probes close to the star, where forbidden lines are quenched, which will help understand accretion ejection when observed with high spatial resolution instruments such as VLTI/AMBER.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

NEAR-IR H{sub 2} EMISSION OF PROTOSTARS: PROBING CIRCUMSTELLAR ENVIRONMENTS

We present new observations of near-infrared molecular hydrogen (H{sub 2}) line emission in a sample of 18 Class I and flat-spectrum low-mass protostars, primarily in the Tau-Aur and {rho} Oph dark clouds. The line emission is extended by up to several arcseconds (several hundred AU) for most objects, and there is little night-to-night variation in line strength coincident with the continuum point source. Flux ratios of H{sub 2} v = 2-1 S(1) and v = 1-0 S(1) lines are consistent with this emission arising in jets or winds in many objects. However, most objects have only small offsets (under 10 km s{sup -1}) between their H{sub 2} and photospheric radial velocities. No objects have line ratios which are clearly caused solely by UV excitation, but the H{sub 2} emission of several objects may be caused by UV or X-ray excitation in the presence of circumstellar dust. There are several objects in the sample whose observed velocities and line fluxes suggest quiescent, non-mechanical origins for their molecular hydrogen emissions. Overall, we find the H{sub 2} emission properties of these protostars to be similar to the T Tauri stars studied in previous surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE CONTRIBUTION OF TP-AGB AND RHeB STARS TO THE NEAR-IR LUMINOSITY OF LOCAL GALAXIES: IMPLICATIONS FOR STELLAR MASS MEASUREMENTS OF HIGH-REDSHIFT GALAXIES

Using high spatial resolution Hubble Space Telescope WFC3 and Advanced Camera for Surveys imaging of resolved stellar populations, we constrain the contribution of thermally pulsing asymptotic giant branch (TP-AGB) stars and red helium burning (RHeB) stars to the 1.6 {mu}m near-infrared (NIR) luminosities of 23 nearby galaxies, including dwarfs and spirals. The TP-AGB phase contributes as much as 17% of the integrated F160W flux, even when the red giant branch is well populated. The RHeB population contribution can match or even exceed the TP-AGB contribution, providing as much as 21% (18% after a statistical correction for foreground) of the integrated F160W light. We estimate that these two short-lived phases may account for up to 70% of the rest-frame NIR flux at higher redshift. The NIR mass-to-light (M/L) ratio should therefore be expected to vary significantly due to fluctuations in the star formation rate (SFR) over timescales from 25 Myr to several Gyr, an effect that may be responsible for some of the lingering scatter in NIR galaxy scaling relations such as the Tully-Fisher and metallicity-luminosity relations. We compare our observational results to predictions based on optically derived star formation histories and stellar population synthesis (SPS) models, including models based on the 2008 Padova isochrones (used in popular SPS programs) and the updated 2010 Padova isochrones, which shorten the lifetimes of low-mass (old) low-metallicity TP-AGB populations. The updated (2010) SPS models generally reproduce the expected numbers of TP-AGB stars in the sample; indeed, for 65% of the galaxies, the discrepancy between modeled and observed numbers is smaller than the measurement uncertainties. The weighted mean model/data number ratio for TP-AGB stars is 1.5 (1.4 with outliers removed) with a standard deviation of 0.5. The same SPS models, however, give a larger discrepancy in the F160W flux contribution from the TP-AGB stars, overpredicting the flux by a weighted mean factor of 2.3 (2.2 with outliers removed) with a standard deviation of 0.8. This larger offset is driven by the prediction of modest numbers of high-luminosity TP-AGB stars at young (<300 Myr) ages. The best-fit SPS models simultaneously tend to underpredict the numbers and fluxes of stars on the RHeB sequence, typically by a factor of 2.0 {+-} 0.6 for galaxies with significant numbers of RHeBs. Possible explanations for both the TP-AGB and RHeB model results include (1) difficulties with measuring the SFHs of galaxies especially on the short timescales over which these stars evolve (several Myr), (2) issues with the way the SPS codes populate the color-magnitude diagrams (e.g., how they handle pulsations or self-extinction), and/or (3) lingering issues with the lifetimes of these stars in the stellar evolution codes. Coincidentally these two competing discrepancies-overprediction of the TP-AGB and underprediction of the RHeBs-result in a predicted NIR M/L ratio largely unchanged for a rapid SFR, after correcting for these effects. However, the NIR-to-optical flux ratio of galaxies could be significantly smaller than AGB-rich models would predict, an outcome that has been observed in some intermediate-redshift post-starburst galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DETECTION OF POWERFUL MID-IR H{sub 2} EMISSION IN THE BRIDGE BETWEEN THE TAFFY GALAXIES

We report the detection of strong, resolved emission from warm H{sub 2} in the Taffy galaxies and bridge. Relative to the continuum and faint polyclic aromatic hydrocarbon (PAH) emission, the H{sub 2} emission is the strongest in the connecting bridge, approaching L(H{sub 2})/L(PAH 8 {mu}m) = 0.1 between the two galaxies, where the purely rotational lines of H{sub 2} dominate the mid-infrared spectrum in a way very reminiscent of the group-wide shock in the interacting group Stephan's Quintet (SQ). The surface brightness in the 0-0 S(0) and S(1) H{sub 2} lines in the bridge is more than twice that observed at the center of the SQ shock. We observe a warm H{sub 2} mass of 4.2 Multiplication-Sign 10{sup 8} M{sub Sun} in the bridge, but taking into account the unobserved bridge area, the total warm mass is likely to be twice this value. We use excitation diagrams to characterize the warm molecular gas, finding an average surface mass of {approx}5 Multiplication-Sign 10{sup 6} M{sub Sun} kpc{sup -2} and typical excitation temperatures of 150-175 K. H{sub 2} emission is also seen in the galaxy disks, although there the emission is more consistent with normal star-forming galaxies. We investigate several possible heating mechanisms for the bridge gas but favor the conversion of kinetic energy from the head-on collision via turbulence and shocks as the main heating source. Since the cooling time for the warm H{sub 2} is short ({approx}5000 yr), shocks must be permeating the molecular gas in the bridge region in order to continue heating the H{sub 2}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Discovery of a population of bulgeless galaxies with extremely red MID-IR colors: Obscured AGN activity in the low-mass regime?

In contrast to massive, bulge hosting galaxies, very few supermassive black holes (SMBHs) are known in either low-mass or bulgeless galaxies. Such a population could provide clues to the origins of SMBHs and to secular pathways for their growth. Using the all-sky Wide-field Infrared Survey Explorer (WISE ) survey, and bulge-to-disk decompositions from the Sloan Digital Sky Survey (SDSS) Data Release 7, we report the discovery of a population of local (z < 0.3) bulgeless disk galaxies with extremely red mid-infrared colors which are highly suggestive of a dominant active galactic nucleus (AGN), despite having no optical AGN signatures in their SDSS spectra. Using various mid-infrared selection criteria from the literature, there are between 30 and over 300 bulgeless galaxies with possible AGNs. Other known scenarios that can heat the dust to high temperatures do not appear to explain the observed colors of this sample. If these galaxies are confirmed to host AGNs, this study will provide a breakthrough in characterizing the properties of SMBHs in the low bulge mass regime and in understanding their relation with their host galaxies. Mid-infrared selection identifies AGNs that dominate their host galaxy's emission and therefore reveal a different AGN population than that uncovered by optical studies. We find that the fraction of all galaxies identified as candidate AGNs by WISE is highest at lower stellar masses and drops dramatically in higher mass galaxies, in striking contrast to the findings from optical studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Emission from water vapor and absorption from other gases at 5-7.5 μm in Spitzer-IRS Spectra Of Protoplanetary Disks

We present spectra of 13 T Tauri stars in the Taurus-Auriga star-forming region showing emission in Spitzer Space Telescope Infrared Spectrograph 5-7.5 μm spectra from water vapor and absorption from other gases in these stars' protoplanetary disks. Seven stars' spectra show an emission feature at 6.6 μm due to the ν{sub 2} = 1-0 bending mode of water vapor, with the shape of the spectrum suggesting water vapor temperatures >500 K, though some of these spectra also show indications of an absorption band, likely from another molecule. This water vapor emission contrasts with the absorption from warm water vapor seen in the spectrum of the FU Orionis star V1057 Cyg. The other 6 of the 13 stars have spectra showing a strong absorption band, peaking in strength at 5.6-5.7 μm, which for some is consistent with gaseous formaldehyde (H{sub 2}CO) and for others is consistent with gaseous formic acid (HCOOH). There are indications that some of these six stars may also have weak water vapor emission. Modeling of these stars' spectra suggests these gases are present in the inner few AU of their host disks, consistent with recent studies of infrared spectra showing gas in protoplanetary disks.

79 ASTRONOMY AND ASTROPHYSICS↗