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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Every Good Virtue You Ever Wanted in a Q-switched Solid-state Laser and More: Monolithic, Diode-pumped, Self-q-switched, Highly Reproducible, Diffraction-limited Nd:yag Laser

The applications of Q-switched lasers are well known, for example, laser radar, laser remote sensing, satellite orbit determination, Moon orbit and 'moon quake' determination, satellite laser communication, and many nonlinear optics applications. Most of the applications require additional properties of the Q-switched lasers, such as single-axial and/or single-transverse mode, high repetition rate, stable pulse shape and pulse width, or ultra compact and rugged oscillators. Furthermore, space based and airborne lasers for lidar and laser communication applications require efficient, compact, lightweight, long-lived, and stable-pulsed laser sources. Diode-pumped solid-state lasers (DPSSL) have recently shown the potential for satisfying all of these requirements. We will report on the operating characteristics of a diode-pumped, monolithic, self-Q-switched Cr,Nd:YAG laser where the chromium ions act as a saturable absorber for the laser emission at 1064 nm. The pulse duration is 3.5 ns and the output is highly polarized with an extinction ratio of 700:1. It is further shown that the output is single-longitudinal-mode with transform-limited spectral line width without pulse-to-pulse mode competition. Consequently, the pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25 percent. This self-stabilization mechanism is because the lasing mode bleaches the distributed absorber and establishes a gain-loss grating similar to that used in the distributed feedback semiconductor lasers. A repetition rate above 5 KHz has also been demonstrated. For higher power, this laser can be used for injection seeding an amplifier (or amplifier chain) or injection locking of a power oscillator pumped by diode lasers. We will discuss some research directions on the master oscillator for higher output energy per pulse as well as how to scale the output power of the diode-pumped amplifier(s) to multi-kilowatt average power.

Chen, Y. C.↗
DOE OSTI2021

Comparison of the Capacitances and Switching Losses of 1.2 kV Common-Source and Common- Drain Bidirectional Switch Topologies

Bidirectional, or four-quadrant switches (FQS) can be designed as back-to-back MOSFETs connected in common-drain (CD) or common-source (CS) topologies. CDFQS and CS-FQS assembled from discrete 1.2 kV commercially available SiC power MOSFETs were characterized to obtain capacitance and switching loss values. The CD-FQS exhibited a 1.17x larger turn-on loss compared to the CS-FQS, while the CS-FQS exhibited a 1.52x larger turn-off loss compared to the CD-FQS. The CS-FQS exhibited a lower input capacitance, while the CD-FQS exhibited a lower output and reverse transfer capacitance.

Silicon Carbide, Bidirectional Switch, Switching P↗
DOE OSTI2019

Dual-wavelength Q-switched laser based on a lens-shaped Nd : YAG active element and a Cr{sup 4+}: YAG passive Q-switch

Dual-wavelength Q-switched lasing at wavelengths of 1047 and 1053 nm is achieved in a longitudinally diode-pumped laser with a lens-shaped Nd:YLF active element and a Cr{sup 4+} : YAG passive Q-switch. Dual-wavelength lasing is achieved as a result of transverse mode locking due to the choice of a cavity length corresponding to the close-to-semiconfocal configuration, which provides identical gains for the two laser wavelengths. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Switching between the mode-locking and Q-switching modes in two-section QW lasers upon a change in the absorber properties due to the Stark effect

The passive Q-switching and mode-locking modes are implemented in two-section lasers with three quantum wells. It is demonstrated that raising the reverse bias on the absorbing section changes its spectral and dynamic properties and, accordingly, leads to a change from the Q-switching mode to mode-locking. The pulse-repetition frequency in the mode-locking mode is 75 GHz, with the product of the pulse duration by the spectrum bandwidth being 0.49, which is close to the theoretical limit. It is shown that, in structures with three quantum wells, strong absorption at the lasing wavelength gives rise to a photocurrent across a section of the saturable absorber, which is sufficient for compensation of the applied bias.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Safety Related Concerns with Installation and Use of Switch-Rated Plug/Receptacle Combinations in Lieu of Metal-Enclosed Disconnect Switches

The manufacturers of Nationally Recognized Testing Laboratory (NRTL) listed, switch-rated, plug and receptacle combinations tout their convenience, reliability, efficiency, and compliance with both the National Fire Protection Association (NFPA) 70®, National Electric Code (NEC), and National Fire Protection Association 70E®, The Standard for Electrical Safety in the Workplace, as advantages to using these products in lieu of traditional metal-enclosed disconnect switches. The purpose of this paper is to raise awareness of several unintended consequences that can result when replacement involves high energy cord and plug connected equipment. This paper describes several possible issues in complying with the NFPA 70 Articles 110 and 400 and NFPA 70E Articles 110 and 130 that should be considered when using load rated plug/receptacle combinations. This paper is intended to address high energy circuits typically associated with 480 volt pin and sleeve type connections in applications where incident energy levels may exceed 1.2 calories/centimeter² (cal/cm²).

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2016

Controlled Generation of Singlet Oxygen in Living Cells with Tunable Ratios of the Photochromic Switch in Metal–Organic Frameworks

Abstract Development of a photosensitizing system that can reversibly control the generation of singlet oxygen ( 1 O 2 ) is of great interest for photodynamic therapy (PDT). Recently several photosensitizer–photochromic‐switch dyads were reported as a potential means of the 1 O 2 control in PDT. However, the delivery of such a homogeneous molecular dyad as designed (e.g., optimal molar ratio) is extremely challenging in living systems. Herein we show a Zr‐MOF nanoplatform, demonstrating energy transfer‐based 1 O 2 controlled PDT. Our strategy allows for tuning the ratios between photosensitizer and the switch molecule, enabling maximum control of 1 O 2 generation. Meanwhile, the MOF provides proximal placement of the functional entities for efficient intermolecular energy transfer. As a result, the MOF nanoparticle formulation showed enhanced PDT efficacy with superior 1 O 2 control compared to that of homogeneous molecular analogues.

Park, Jihye↗
DOE OSTI2016

Evaluation of a commercially available passively Q-switched Nd:YAG laser with LiF:F-2(-) saturable absorber for laser-induced breakdown spectroscopy

Interest in passively Q-switched microchip lasers as a means for miniaturization of laser-induced breakdown spectroscopy (LIBS) apparatus has rapidly grown in the last years. To explore the possibility of using a comparatively UV-Vis transparent absorber, we herein present the first report on the evaluation of a commercially available flash lamp-pumped passively Q-switched Nd:YAG laser with LiF:F 2 - saturable absorber as an excitation source in LIBS. Quantitative measurements of barium, strontium, rubidium and lithium in granite, rhyolite, basalt and syenite whole-rock glass samples were performed. Ablation craters produced on a rock glass sample were characterized using a computerized X-ray tomography. Using a gated intensified benchtop spectrometer, limits of detection of 0.97, 23, 37, and 144 ppm were obtained for Li, Sr, Rb, and Ba, respectively. Finally, we discuss the advantages of using such a laser unit for LIBS applications in terms of ablation efficiency, analytical performances, output energy, and standoff capabilities.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber

Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. As a result, by combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A microbial sensor for organophosphate hydrolysis exploiting an engineered specificity switch in a transcription factor

A whole-cell biosensor utilizing a transcription factor (TF) is an effective tool for sensitive and selective detection of specialty chemicals or anthropogenic molecules, but requires access to an expanded repertoire of TFs. Using homology modeling and ligand docking for binding pocket identification, assisted by conservative mutations in the pocket, we engineered a novel specificity in an Acinetobacter TF, PobR, to ‘sense’ a chemical p-nitrophenol (pNP) and measured the response via a fluorescent protein reporter expressed from a PobR promoter. Out of 107 variants of PobR, four were active when dosed with pNP, with two mutants showing a specificity switch from the native effector 4-hydroxybenzoate (4HB). One of the mutants, pNPmut1 was then used to create a smart microbial cell responding to pNP production from hydrolysis of an insecticide, paraoxon, in a coupled assay involving phosphotriesterase (PTE) enzyme expressed from a separate promoter. We show the fluorescence of the cells correlated with the catalytic efficiency of the PTE variant expressed in each cell. High selectivity between similar molecules (4HB versus pNP), high sensitivity for pNP detection (~2 μM) and agreement of apo- and holo-structures of PobR scaffold with predetermined computational models are other significant results presented in this work.

Jha, Ramesh K.↗
DOE OSTI2022

Electronegative metal dopants improve switching variability in Al 2 ⁢O 3 resistive switching devices

Resistive random-access memories are promising for nonvolatile memory and brain-inspired computing applications. High variability and low yield of these devices are key drawbacks hindering reliable training of physical neural networks. In this paper, we show that doping an oxide electrolyte, Al 2 ⁢O 3 , with electronegative metals makes resistive switching significantly more reproducible, surpassing the reproducibility requirements for obtaining reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. Throughout this work, we validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of Al 2 ⁢O 3 and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Neutron and X-ray investigations of the Jahn–Teller switch in partially deuterated ammonium copper Tutton salt, (NH 4 ) 2 [Cu(H 2 O) 6 ](SO 4 ) 2

The structural phase transition accompanied by a Jahn–Teller switch has been studied over a range of H/D ratios in (NH 4 ) 2 [Cu(H 2 O) 6 ](SO 4 ) 2 (ACTS). In particular, single-crystal neutron diffraction investigations of crystals with deuteration in the range 50 to 82% are shown to be consistent with previous electron paramagnetic resonance (EPR) experiments exhibiting a phase boundary at 50% deuteration under ambient pressure. Polycrystalline samples show that the two phases can co-exist. In addition, single-crystal neutron and polycrystalline X-ray diffraction pressure experiments show a shift to lower pressure at 60% deuteration versus previous measurements at 100% deuteration.

deuterium isotope phase transition↗
DOE OSTI2024

High-temperature quantum valley Hall effect with quantized resistance and a topological switch

Edge states of a topological insulator can be used to explore fundamental science emerging at the interface of low dimensionality and topology. Achieving a robust conductance quantization, however, has proven challenging for helical edge states. In this work, we show wide resistance plateaus in kink states—a manifestation of the quantum valley Hall effect in Bernal bilayer graphene—quantized to the predicted value at zero magnetic field. The plateau resistance has a very weak temperature dependence up to 50 kelvin and is flat within a dc bias window of tens of millivolts. We demonstrate the electrical operation of a topology-controlled switch with an on/off ratio of 200. These results demonstrate the robustness and tunability of the kink states and its promise in constructing electron quantum optics devices.

Science & Technology - Other Topics↗
DOE OSTI2017

A single mutation in Taiwanese H6N1 influenza hemagglutinin switches binding to human‐type receptors

Abstract In June 2013, the first case of human infection with an avian H6N1 virus was reported in a Taiwanese woman. Although this was a single non‐fatal case, the virus continues to circulate in Taiwanese poultry. As with any emerging avian virus that infects humans, there is concern that acquisition of human‐type receptor specificity could enable transmission in the human population. Despite mutations in the receptor‐binding pocket of the human H6N1 isolate, it has retained avian‐type (NeuAcα2‐3Gal) receptor specificity. However, we show here that a single nucleotide substitution, resulting in a change from Gly to Asp at position 225 (G225D), completely switches specificity to human‐type (NeuAcα2‐6Gal) receptors. Significantly, G225D H6 loses binding to chicken trachea epithelium and is now able to bind to human tracheal tissue. Structural analysis reveals that Asp225 directly interacts with the penultimate Gal of the human‐type receptor, stabilizing human receptor binding.

de Vries, Robert P.↗
NASA NTRS1967

Hybrid solid state switch replaces motor- driven power switch

Hybrid solid state switch replaces existing motor-driven power switches used on spacecraft. It uses a transistor circuit to limit the open circuit voltage and allow small relay contacts to handle high transient currents at reasonable cycle life.

Booth, R. A.↗
NASA NTRS1993

Characteristics of switching plasma in an inverse-pinch switch

Characteristics of the plasma that switches on tens of giga volt-ampere in an inverse-pinch plasma switch (INPIStron) have been made. Through optical and spectroscopic diagnostics of the current carrying plasma, the current density, the motion of current paths, dominant ionic species have been determined in order to access their effects on circuit parameters and material erosion. Also the optimum operational condition of the plasma-puff triggering method required for azimuthally uniform conduction in the INPIStron has been determined.

Lee, Ja H.↗
NASA NTRS2002

MEMS, Ka-Band Single-Pole Double-Throw (SPDT) Switch for Switched Line Phase Shifters

Ka-band MEMS doubly anchored cantilever beam capacitive shunt devices are used to demonstrate a MEMS SPDT switch fabricated on high resistivity silicon (HRS) utilizing finite ground coplanar waveguide (FGC) transmission lines. The SPDT switch has an insertion loss (IL), return loss (RL), and isolation of 0.3dB, 40dB, and 30 dB, respectively at Ka-band.

Scardelletti, Maximilian C.↗
DOE OSTI2018

Simultaneous Switching of Multiple GaN Transistors in a High-Speed Switch

broadband travelling wave kicker operating with 80 MHz repetition rates is required for the new PIP-II accelerator at Fermilab. We present a technique to drive simultaneously four series-connected enhancement mode GaN-on-silicon power transistors by means of microwave photonics techniques. These four transistors are arranged into a high voltage and high repetition rate switch. Using multiple transistors in series is required to share switching losses. Using a photonic signal distribution system is required to achieve precise synchronization between transistors. We demonstrate 600 V arbitrary pulse generation into a 200 Ohm load with 2 ns rise/fall time. The arbitrary pulse widths can be adjusted from 4 ns to essentially DC.

Frolov, Daniil↗
DOE OSTI2016

Investigation of a gain-switched Cr{sup 2+}:ZnSe laser pumped by an acousto-optic Q-switched Ho : YAG laser

We demonstrate a gain-switched Cr{sup 2+}:ZnSe laser pumped by a high energy Ho : YAG laser. The maximum output power of 5.5 W in the spectrum range from 2450 nm to 2570 nm is obtained at a pulse repetition rate of 2 kHz, corresponding to a pulse energy of 2.75 mJ. With a volume Bragg grating (VBG) for compressing the linewidth, a 2.4 W output power with a narrow linewidth (<1 nm) is obtained at 2570.5 nm. The pulse shapes obtained at different pump energies are also studied and analysed. A minimum pulse width of ∼28.5 ns is achieved at a pump energy of 14.6 mJ, corresponding to a peak power of ∼96.5 kW. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗