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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evidence for ionization damage in mid-wave infrared nBn detectors

The effects of 63 MeV proton and 60Co gamma irradiation on the operation of 4.3 μm cutoff nBn photodetectors are demonstrated separately, and both are shown to yield a total ionizing dose (TID) effect. The effect is shown here in an InAsSbBi nBn detector and has been observed in other bulk alloy nBn detectors, and is unusual as it is notably absent in superlattice nBn detectors. The non-antireflection coated detectors exhibit a pre-radiation quantum efficiency of 17% at 3.3 μm wavelength and a dark current density of 50 μA/cm2, or roughly 300× the Rule 07 expectation, at their ideal operating voltage of −0.4 V bias at 150 K. Step-wise proton irradiation and in situ measurement indicate that the dark current increases to about 400× Rule 07 at the highest proton dose level of 150 krad(Si) (9.10 × 1011 p+/cm2), while the quantum efficiency is degraded at a relatively faster rate than the majority of analogous detectors characterized by our lab. Both the photocurrent and dark current are also shown to exhibit a turn-on voltage magnitude reduction of 100 mV following either gamma or proton irradiation, a trend which is attributable to negative trapped charge at the barrier interface (TID effect). This theory is further supported by an observed capacitance density magnitude reduction with dose and affirmed with Silvaco TCAD simulations. Following both proton exposure and subsequent anneal and gamma exposure and subsequent anneal; dark current, photocurrent, and CV all approach their pre-radiation baseline values.

Physics↗
DOE OSTI2024

Carbon-related donor–acceptor pair transition in the infrared in h-BN

Experimental studies of intentionally doped impurities for the understanding of conductivity control in hexagonal boron nitride (h-BN) ultrawide bandgap (UWBG) semiconductor are limited but are highly desired for emerging applications of h-BN. We report synthesis by hydride vapor phase epitaxy and comparison photoluminescence (PL) emission spectroscopy studies of intentionally carbon (C)-doped and undoped h-BN semi-bulk crystals. In addition to the well-known C-related emission lines observed previously, a C-impurity-related transition near 1.31 eV consisting of multiple phonon replicas has been observed in C-doped h-BN at room temperature. Phonon replicas involved in the 1.31 eV emission have been identified using polarization resolve PL spectroscopy as the transverse acoustic (TA)/longitudinal acoustic (LA) and out-of-plane optical phonon (ZO) modes at the middle point, T, between the Γ- and K-points in the first Brillouin zone. Based on the agreement between the spectral peak position of the observed dominant emission line at 1.31 eV and the calculated energy-level separation between CB donor (carbon replacing boron) and Ci acceptor (carbon interstitial), the observed IR emission line can be decisively assigned to the donor–acceptor pair (DAP) transition involving the CB donor and Ci acceptor assisted by the intervalley (Κ → Μ) scattering processes. The results reinforce the perception that C impurities form deep-level centers and provided an improved understanding of C impurities in h-BN.

Physics↗
DOE OSTI2024

Infrared spectroscopy of the syn -methyl-substituted Criegee intermediate: A combined experimental and theoretical study

An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies.

Chemistry↗
DOE OSTI2025

Thermoradiative energy conversion in infrared interband cascade InAs/GaSb/AlInSb/GaSb type-II superlattice diodes

Thermoradiative energy conversion presents a means for the direct conversion of thermal energy through radiative transfer to a cold scene. However, much of the study of thermoradiative principles has been based on theory and simulations, with only sparse reports on the experimental demonstration of the concept. This work studies thermoradiative energy conversion in InAs/GaSb/AlInSb/GaSb type-II superlattice cascade devices. The devices exhibit a cutoff wavelength of 3.2 μm at 300 K, corresponding to a bandgap of 0.39 eV. Testing under a temperature-controlled chamber and scene demonstrates a maximum power density of 2.9 mW/m2 at a cell temperature of 121 °C. It is consistent with expected values for device operation limited by Shockley–Read–Hall non-radiative recombination. This result is a significant step in providing an experimental demonstration of thermoradiative energy conversion and a means to characterize cell performance, providing a foundation for further development to achieve practical values for power generation.

Islam, Md Toriqul (ORCID:0000000249871320)↗
DOE OSTI2024

Software For Automated Leak Detection Using Infrared Camera

This code can read in videos or images in either a batch or real-time format. Videos are broken up into frames, and the frames are processed using an optical flow algorithm to decipher movement between adjacent frames. This adherent movement is ran through a convolutional neural network that automatically classifies the contents of the video. Additional content inside the code aids with noisy images and removal of nuisance movement.

Walker, CodyM. [Idaho National Laboratory (INL), I↗
DOE OSTI2025

Laser damage of crazed electron-beam high-reflectors following infrared and ultraviolet irradiation in the nanosecond pulse regime

Laser damage of optical components can be a limiting factor in scaling the energetics of high-peak and average power laser systems. Specifically for optical coatings, damage under nanosecond pulsed irradiation is initiated by pre-existing defects in the coating layers, including those that cause discontinuities in the structure, like craze lines. Crazing or cracking in a multilayer dielectric optical coating is induced when the overall coating stress is sufficiently tensile, and is an occasionally observed issue when employing more porous deposition techniques like electron-beam evaporation. Here, in this study, electron-beam high-reflectors were fabricated utilizing process parameters that are known to induce crazing based on prior processing history to systematically evaluate the impact of crazing on reflector damage performance for 1064 and 355 nm lasers. The crazing that was observed was apparently nucleated at nodular defects. When the cross-section of these nodules was investigated, it was observed that there were cracks into the fused silica substrate of approximately 5 µm in depth. The craze lines were irradiated with 1064 and 355 nm light at fluences slightly above the onset of damage initiation fluence of the coating. The 1064 nm irradiated sub-apertures exhibit laser damage but with no spatial correlation with the craze line, whereas the 355 nm irradiated area exhibited many damage sites along the craze line. Finite-difference time-domain electric-field simulations were conducted, and ∼2× field amplification in hafnia was observed for the 355 nm wavelength case. The laser damage can be attributed to a slight electric-field intensification coincidental with an area where UV damage-prone precursors are known to occur. The 355 nm laser damage in uncoated fused silica substrates has been previously correlated to initiate through localized UV absorption at the broken silica bonds in the tips of fractures.

Harthcock, Colin [Lawrence Livermore National Labo↗
DOE OSTI2025

High-repetition rate, CEP-stable shortwave infrared source with two-cycle pulses for field-resolved spectroscopy

We report on a passively carrier-envelope phase (CEP)-stable optical parametric amplifier generating two-cycle pulses at 2060 nm with energies of up to 2.25 µJ operating at a repetition rate of 400 kHz, specifically designed for applications in field-resolved spectroscopy. The measured pulse duration is 13.6 fs, resulting in two cycles of the carrier wave. Due to the robust CEP-stable front-end design, we achieve an open-loop CEP stability of 250 mrad (rms) and the capability for fast CEP modulation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Constructing the infrared conformal generators on the fuzzy sphere

We investigate the conformal algebra on the fuzzy sphere, and in particular the generators of translations and special conformal transformations which are emergent symmetries in the infinite IR but are broken along the RG flow. We show how to extract these generators using the energy momentum tensor, which is complicated by the fact that one does not have a priori access to the energy momentum tensor of the CFT limit but rather must construct it numerically. We discuss and quantitatively analyze the main sources of corrections to the conformal generators due to the breaking of scale-invariance at finite energy, and develop efficient methods for removing these corrections. The resulting generators have matrix elements that match CFT predictions with accuracy varying from sub-percent level for the lowest-lying states up to several percent accuracy for states with dimension \sim 5 ∼ 5 with N=16 N = 16 fermions. We show that the generators can be used to accurately identify primary operators vs descendant operators in energy ranges where the spectrum is too dense to do the identification solely based on the approximate integer spacing within conformal multiplets.

Fardelli, Giulia (ORCID:0000000217998124)↗