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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Two wavelength satellite laser ranging using SPAD

When ranging to satellites with lasers, there are several principal contributions to the error budget: from the laser ranging system on the ground, from the satellite retroarray geometry, and from the atmosphere. Using a single wavelength, we have routinely achieved a ranging precision of 8 millimeters when ranging to the ERS-1 and Starlette satellites. The systematic error of the atmosphere, assuming the existing dispersion models, is expected to be of the order of 1 cm. Multiple wavelengths ranging might contribute to the refinement of the existing models. Taking into account the energy balance, the existing picosecond lasers and the existing receiver and detection technology, several pairs or multiple wavelengths may be considered. To be able to improve the atmospheric models to the subcentimeter accuracy level, the differential time interval (DTI) has to be determined within a few picoseconds depending on the selected wavelength pair. There exist several projects based on picosecond lasers as transmitters and on two types of detection techniques: one is based on photodetectors, like photomultipliers or photodiodes connected to the time interval meters. Another technique is based on the use of a streak camera as an echo signal detector, temporal analyzer, and time interval vernier. The temporal analysis at a single wavelength using the streak camera showed the complexity of the problem.

Prochazka, Ivan↗
NASA NTRS2003

Looking for Speed!! Go Optical Ultra-Fast Photonic Logic Gates for the Future Optical Communication and Computing

Recently, we developed two ultra-fast all-optical switches in the nanosecond and picosecond regimes. The picosecond switch is made of a polydiacetylene thin film coated on the interior wall of a hollow capillary of approximately 50 micron diameter by a photo-polymerization process. In the setup a picosecond Nd:YAG laser at 10 Hz and at 532 nm with a pulse duration of approximately 40 ps was sent collinearly along a cw He-Ne laser beam and both were waveguided through the hollow capillary. The setup functioned as an Exclusive OR gate. On the other hand, the material used in the nanosecond switch is a phthalocyanine thin film, deposited on a glass substrate by a vapor deposition technique. In the setup a nanosecond, 10 Hz, Nd:YAG laser of 8 ns pulse duration was sent collinearly along a cw He-Ne laser beam and both were wave-guided through the phthalocyanine thin film. The setup in this case functioned as an all-optical AND logic gate. The characteristic table of the ExOR gate in polydiacetylene film was attributed to an excited state absorption process, while that of the AND gate was attributed to a saturation process of the first excited state. Both mechanisms were thoroughly investigated theoretically and found to agree remarkably well with the experimental results. An all-optical inverter gate has been designed but has not yet been demonstrated. The combination of all these three gates form the foundation for building all the necessary gates needed to build a prototype of an all-optical system.

Abdeldayem, Hossin↗
NASA NTRS2010

Simultaneous Spectral Temporal Adaptive Raman Spectrometer - SSTARS

Raman spectroscopy is a prime candidate for the next generation of planetary instruments, as it addresses the primary goal of mineralogical analysis, which is structure and composition. However, large fluorescence return from many mineral samples under visible light excitation can render Raman spectra unattainable. Using the described approach, Raman and fluorescence, which occur on different time scales, can be simultaneously obtained from mineral samples using a compact instrument in a planetary environment. This new approach is taken based on the use of time-resolved spectroscopy for removing the fluorescence background from Raman spectra in the laboratory. In the SSTARS instrument, a visible excitation source (a green, pulsed laser) is used to generate Raman and fluorescence signals in a mineral sample. A spectral notch filter eliminates the directly reflected beam. A grating then disperses the signal spectrally, and a streak camera provides temporal resolution. The output of the streak camera is imaged on the CCD (charge-coupled device), and the data are read out electronically. By adjusting the sweep speed of the streak camera, anywhere from picoseconds to milliseconds, it is possible to resolve Raman spectra from numerous fluorescence spectra in the same sample. The key features of SSTARS include a compact streak tube capable of picosecond time resolution for collection of simultaneous spectral and temporal information, adaptive streak tube electronics that can rapidly change from one sweep rate to another over ranges of picoseconds to milliseconds, enabling collection of both Raman and fluorescence signatures versus time and wavelength, and Synchroscan integration that allows for a compact, low-power laser without compromising ultimate sensitivity.

Blacksberg, Jordana↗
NASA NTRS2012

Two Years of Simultaneous K(sub a)-Band Measurements: Goldstone, CA; White Sands, NM; and Guam, USA

In order to statistically characterize the effect of the Earth's atmosphere on Ka-Band links, site test interferometers (STIs) have been deployed at three of NASA s operational sites to directly measure each site's tropospheric phase stability and rain attenuation. These STIs are composed of two antennas on a short baseline (less than 1km) that observe the same unmodulated beacon signal broadcast from a geostationary satellite (e.g., Anik F2). The STIs are used to measure the differential phase between the two received signals as well as the individual signal attenuation at each terminal. There are currently three NASA sites utilizing STIs; the Goldstone Deep Space Communications Complex near Barstow, California; the White Sands Complex in Las Cruces, New Mexico; and the Guam Remote Ground Terminal on the island of Guam. The first two sites are both located in desert regions that have highly similar climates in terms of their seasonal temperatures, average humidity, and annual rain fall (the primary factors in determining phase stability). In contrast, Guam is in a tropical region with drastically higher annual rainfall and humidity. Five station years of data have been collected in Goldstone, three in White Sands, and two in Guam, yielding two years of simultaneous data collection across all three sites. During this period of simultaneous data collection, the root-mean-square (RMS) of the time delay fluctuations stayed under 2.40 picoseconds for 90% of the time in Goldstone, under 2.07 picoseconds for 90% of the time in White Sands, and under 10.13 picoseconds for 90% of the time in Guam. For the 99th percentile, the statistics were 6.32 ps, 6.03 ps, and 24.85 ps, respectively. These values, as well as various other site quality characteristics, will be used to determine the suitability of these sites for NASA s future communication services at Ka-Band.

Acosta, Roberto J.↗
DOE OSTI2021

Cadmium Magnesium Telluride for Next Generation X-Ray Free Electron Laser, Synchrotron and Many Other Applications

We developed a picosecond photodetector based on our Bridgman grown and specially engineered Cadmium Magnesium Telluride (Cd 1-x Mg x Te) single crystal that is sensitive to both optical and x-ray pulses for coarse timing in Free Electron Laser applications. Cd 1-x Mg x Te is a wide bandgap semiconductor material with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma ray radiation, thermal neutrons, and medical imaging. However, for femtosecond optical and x-ray cross correlation, the material has to have very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have very low bulk leakage current, in the 0.10 pA range. Hence the ability to tailor or engineer the material is very crucial. In this paper, picosecond response and the crystal growth of this specially engineered cadmium magnesium telluride material will be presented. Other material characterization and transient measurements will also be discussed along with room temperature semiconductor detector performance for other nuclear radiation detection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cadmium Magnesium Telluride for Next-Generation X-Ray Free Electron Laser, Synchrotron, and Many Other Applications

We developed a picosecond photodetector based on our Bridgman-grown and specially engineered cadmium magnesium telluride (Cd 1–x MgxTe) single crystal that is sensitive to both optical and X-ray pulses for coarse timing in free-electron laser applications. Cd 1–x MgxTe is a widebandgap semiconductor with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma-ray radiation, thermal neutrons, and medical imaging. For femtosecond optical and X-ray crosscorrelation, the material must have a very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have a very low bulk leakage current, in the 10–90 nA range for voltages to even 1000 V. Hence, the ability to tailor or engineer the material is very crucial. Picosecond response and the crystal growth of this specially engineered Cd 1–x MgxTe material are presented. Furthermore, other characterization and transient measurements are discussed along with room-temperature semiconductor detector performance for other nuclear radiation detection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development of an MCP-Based Timing Layer for the LHCb ECAL Upgrade-2

The increase in instantaneous luminosity during the high-luminosity phase of the LHC represents a significant challenge for future detectors. A strategy to cope with high-pileup conditions is to add a fourth dimension to the measurements of the hits, by exploiting the time separation of the various proton–proton primary collisions. According to LHCb simulation studies, resolutions of about 10–20 picoseconds, at least an order of magnitude shorter than the average time span between primary interactions, would be greatly beneficial for the physics reach of the experiment. Microchannel plate (MCP) photomultipliers are compact devices capable of measuring the arrival time of charged particles with the required resolution. The technology of large-area picosecond photodetectors (LAPPDs) is under investigation to implement a timing layer that can be placed within a sampling calorimeter module with the purpose of measuring the arrival time of electromagnetic showers. LAPPD performances, using a Gen-I tile with a delay-line anode and a Gen-II with a capacitively coupled anode, have been measured thoroughly both with laser (wavelength of 405 nm and pulse width of 27.5 ps FWHM) and high-energy electron (1–5.8 GeV) beams. Time resolutions of the order of 30 ps for single photoelectrons and 15 ps for electromagnetic showers initiated by 5-GeV electrons, as measured at the shower maximum, are obtained.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Sub‐Nanosecond Reconfiguration of Ferroelectric Domains in Bismuth Ferrite

Abstract Domain switching is crucial for achieving desired functions in ferroic materials that are used in various applications. Fast control of domains at sub‐nanosecond timescales remains a challenge despite its potential for high‐speed operation in random‐access memories, photonic, and nanoelectronic devices. Here, ultrafast laser excitation is shown to transiently melt and reconfigure ferroelectric stripe domains in multiferroic bismuth ferrite on a timescale faster than 100 picoseconds. This dynamic behavior is visualized by picosecond‐ and nanometer‐resolved X‐ray diffraction and time‐resolved X‐ray diffuse scattering. The disordering of stripe domains is attributed to the screening of depolarization fields by photogenerated carriers resulting in the formation of charged domain walls, as supported by phase‐field simulations. Furthermore, the recovery of disordered domains exhibits subdiffusive growth on nanosecond timescales, with a non‐equilibrium domain velocity reaching up to 10 m s −1 . These findings present a new approach to image and manipulate ferroelectric domains on sub‐nanosecond timescales, which can be further extended into other complex photoferroic systems to modulate their electronic, optical, and magnetic properties beyond gigahertz frequencies. This approach could pave the way for high‐speed ferroelectric data storage and computing, and, more broadly, defines new approaches for visualizing the non‐equilibrium dynamics of heterogeneous and disordered materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Broadband Ultrafast Dynamics of Refractory Metals: TiN and ZrN

Transition metal nitrides have recently gained attention in the fields of plasmonics, plasmon-enhanced photocatalysis, photothermal applications, and nonlinear optics because of their suitable optical properties, refractory nature, and large laser damage thresholds. Here we report comparative studies of the transient response of films of titanium nitride (TiN), zirconium nitride (ZrN), and gold (Au) under femtosecond excitation. Broadband transient optical characterization helps to adjudicate earlier, somewhat inconsistent reports regarding hot electron lifetimes based upon single wavelength measurements. These pump–probe experiments show sub-picosecond transient dynamics only within the epsilon-near-zero window of the refractory metals. The dynamics are dominated by photoinduced interband transitions resulting from ultrafast electron energy redistribution. The enhanced reflection modulation in the epsilon-near-zero window makes it possible to observe the ultrafast optical response of these films at low pump fluences. These results indicate that electron–phonon coupling in TiN and ZrN is 25–100 times greater than in Au. Strong electron–phonon coupling drives the sub-picosecond optical response and facilitates greater lattice heating compared to Au, making TiN and ZrN promising for photothermal applications. The spectral response and dynamics of TiN and ZrN are only weakly sensitive to pump fluence and pump excitation energy. However, the magnitude of the response is much greater at higher pump photon energies and higher fluences, reaching peak observed values of 15% in TiN and 50% in ZrN in the epsilon-near-zero window.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In-Situ Observation of the Formation of Laser-Induced Periodic Surface Structures with Extreme Spatial and Temporal Resolution

Irradiation of solid surfaces with intense ultrashort laser pulses represents a unique way of depositing energy into materials. It allows to realize states of extreme electronic excitation and/or very high temperature and pressure and to drive materials close to and beyond fundamental stability limits. As a consequence, structural changes and phase transitions often occur along unusual pathways and under strongly nonequilibrium conditions. Furthermore, due to the inherent multiscale nature—both temporally and spatially—of these irreversible processes, their direct experimental observation requires techniques that combine high temporal resolution with the appropriate spatial resolution and the capability to obtain good quality data on a single pulse/event basis. In this respect, fourth-generation light sources, namely, short wavelength and short pulse free electron lasers (FELs), are offering new and fascinating possibilities. As an example, this chapter will discuss the results of scattering experiments carried out at the FLASH free electron laser at DESY (Hamburg, Germany), which allowed us to resolve laser-induced structure formation at surfaces on the nanometer to submicron length scale and in temporal regimes ranging from picoseconds to several nanoseconds with sub-picosecond resolution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Time-domain modelling and thermometry of the CH 4 v 1 Q-branch using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering

Here, we present time-domain measurements and modelling of the CH 4 v 1 vibrational Q-branch, as well as simultaneous temperature acquisition from the CH 4 and N 2 vibrational Q-branches using broadband hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS). Accurate measurements with fs/ps CARS require knowledge of the time-domain response of the probed molecule at different temperatures and pressures. In this work, a fs/ps CARS model was developed for theCH 4 v 1 Q-branch and validated using time-resolved probe delay scans at pressures between 70 and 600 Torr and temperatures between 295 and 1000 K. A simplified modified exponential energy gap model was used to determine the linewidths of the Raman transitions within the Q-branch. Total Q-branch linewidths for the entire explored parameter space were also determined from the probe delay scans. This enabled quantitative measurements of CH 4 with fs/ps CARS as well as the temperature through the hot bands of the CH 4 v 1 Q-branch. With a broadband fs laser pulse in a two-beam phase matching scheme, the N 2 Q-branch and CH 4 v 1 Q-branch were simultaneously measured in a heated cell, and the temperatures from each molecule's spectra was evaluated. Here, the fitted temperatures corresponded well with differences ranging from 4 to 17%. It was also shown that exchanging 90% of CH 4 for N 2 or Ar at 295 K and 500 Torr did not significantly impact the normalized time-domain signal prior to a 100 picosecond probe delay. Spatially resolved one-dimensional (1-D) thermometry using the CH 4 Q-branch was also demonstrated with an imaged spatial resolution of 40 µm. With the developed model, 1-D quantitative measurements of CH 4 concentration and temperature can be measured with time resolution of tens of picoseconds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Extraordinarily large permittivity modulation in zinc oxide for dynamic nanophotonics

The dielectric permittivity of a material encapsulates the essential physics of light-matter interaction into the material's local response to optical excitation. Photo-induced modulation of the permittivity can enable an unprecedented level of control over the phase, amplitude, and polarization of light. Therefore, the detailed dynamic characterization of technology-relevant materials with substantially tunable optical properties and fast response times is a crucial step to realize tunable optical devices. This work reports on the extraordinarily large permittivity changes in zinc oxide thin films (up to similar to 3.6 relative change in the real part of the dielectric permittivity at 1600 nm wavelength) induced by optically generated free carriers. We demonstrate broadband reflectance modulation up to 70% in metal-backed oxide mirrors at the telecommunication wavelengths, with picosecond-scale relaxation times. The epsilon near zero points of the films can be dynamically shifted from 8.5 mm to 1.6 mm by controlling the pump fluence. Additionally, the modulation can be selectively enhanced at specific wavelengths employing metal-backed zinc oxide disks while maintaining picosecond-scale switching times. This work provides insights into the free-carrier assisted permittivity modulation in zinc oxide and could enable the realization of novel dynamic devices for beam-steering, polarizers, and spatial light modulators.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Evaluation of the absolute single-photon detection efficiency of HRPPD

Pixelated High Rate Picosecond Photon Detectors (HRPPDs) by Incom Inc. are promising photosensors for use in Ring Imaging CHerenkov (RICH) detectors, where a high gain, sub-mm position resolution and sub-100ps timing resolution are required in a single photon mode. Quantum Efficiency (QE) has been measured for the first batch of EIC HRPPDs both by Incom and EIC research groups at Jefferson Lab and Brookhaven Lab, with peak values at ∼365 nm typically exceeding 30%. Furthermore, in this study, we present a first direct measurement of Photon Detection Efficiency being equal to (17.1 ± 0.1 [stat] ± 0.3 [sys])% at 398.6 nm, for a pixel near the center of HRPPD, in a photoelectron pulse counting mode using a picosecond diode laser. HRPPD QE at the same spot and at the same wavelength was evaluated to be (24.4 ± 0.1 [stat] ± 0.3 [sys])%, leading to a Collection Efficiency estimate of (70.3 ± 1.6)%, which is consistent with the expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Kinetics for the reaction between the solvated electron and dissolved oxygen in n-dodecane from 2.5 to 40 °C

Temperature-controlled, time-resolved picosecond electron pulse radiolysis was utilized to measure the rate of reaction between the solvated electron (eS–) and dissolved oxygen in n-dodecane solutions from 2.5 to 40 °C for the first time. At 20.0 °C, the reaction rate was determined to be k(eS– + O2) = (4.54 ± 0.21) × 1010 M-1 s-1, with an activation energy of Ea = 14.4 ± 1.3 kJ mol-1. These newly determined kinetic parameters are important for predicting and managing the effects of aerated environments on the degradation of organic solvents used in nuclear fuel reprocessing technologies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Structural and dynamic effects of paraoxon binding to human acetylcholinesterase by X-ray crystallography and inelastic neutron scattering

Organophosphorus (OP) compounds, including nerve agents and some pesticides, covalently bind to the catalytic serine of human acetylcholinesterase (hAChE), thereby inhibiting acetylcholine hydrolysis necessary for efficient neurotransmission. Oxime antidotes can reactivate the OP-conjugated hAChE, but reactivation efficiency can be low for pesticides, such as paraoxon (POX). Understanding structural and dynamic determinants of OP inhibition and reactivation can provide insights to design improved reactivators. Here, in this study, X-ray structures of hAChE with unaged POX, with POX and oximes MMB4 and RS170B, and with MMB4 are reported. A significant conformational distortion of the acyl loop was observed upon POX binding, being partially restored to the native conformation by oximes. Neutron vibrational spectroscopy combined with molecular dynamics simulations showed that picosecond vibrational dynamics of the acyl loop soften in the ~20–50 cm –1 frequency range. The acyl loop structural perturbations may be correlated with its picosecond vibrational dynamics to yield more comprehensive template for structure-based reactivator design.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Functional Connectivity of Red Chlorophylls in Cyanobacterial Photosystem I Revealed by Fluence-Dependent Transient Absorption

External stressors modulate the oligomerization state of photosystem I (PSI) in cyanobacteria. The number of red chlorophylls (Chls), pigments lower in energy than the P700 reaction center, depends on the oligomerization state of PSI. Here, we use ultrafast transient absorption spectroscopy to interrogate the effective connectivity of the red Chls in excitonic energy pathways in trimeric PSI in native thylakoid membranes of the model cyanobacterium Synechocystis sp. PCC 6803, including emergent dynamics, as red Chls increase in number and proximity. Fluence-dependent dynamics indicate singlet–singlet annihilation within energetically connected red Chl sites in the PSI antenna but not within bulk Chl sites on the picosecond time scale. These data support picosecond energy transfer between energetically connected red Chl sites as the physical basis of singlet–singlet annihilation. The time scale of this energy transfer is faster than predicted by Förster resonance energy transfer calculations, raising questions about the physical mechanism of the process. Our results indicate distinct strategies to steer excitations through the PSI antenna; the red Chls present a shallow reservoir that direct excitations away from P 700 , extending the time to trapping by the reaction center.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Superradiance and Directional Exciton Migration in Metal–Organic Frameworks

Crystalline metal–organic frameworks (MOFs) are promising synthetic analogues of photosynthetic light-harvesting complexes (LHCs). The precise assembly of linkers (organic chromophores) around the topology-defined pores offers the evolution of unique photophysical behaviors that are reminiscence of LHCs. These include MOF excited states with photoabsorbed energy that is spatially dispersed over multiple linkers defining the molecular excitons. The multilinker molecular excitons display superradiance–a hallmark of coupled oscillators seen in LHCs–with radiative rate constant (k rad ) exceeding that of a single linker. Our theoretical model and experimental results on three zirconium MOFs, namely, PCN-222(Zn), NU-1000, and SIU-100, with similar topology but varying linkers suggest that the size of such molecular excitons depends on the electronic symmetry of the linker. This multilinker exciton model effectively predicts the energy transfer rate constant; corresponding single-step exciton hopping time, ranging from a few picoseconds in SIU-100 and NU-1000 to a few hundreds of picoseconds in PCN-222(Zn), matches well with the experimental data. The model also predicts the anisotropy of exciton displacement with preferential migration along the crystallographic c-axis. Overall, these findings establish various missing links defining the exciton size and dynamics in MOF-assembled linkers. Furthermore, the understandings will provide design principles, especially, positioning the catalysts or electrode relative to the linker orientation for low-density solar energy conversion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Exchange-Mediated Transport in Battery Electrolytes: Ultrafast or Ultraslow?

Understanding the mechanisms of charge transport in batteries is important for the rational design of new electrolyte formulations. Persistent questions about ion transport mechanisms in battery electrolytes are often framed in terms of vehicular diffusion by persistent ion–solvent complexes versus structural diffusion through the breaking and reformation of ion–solvent contacts, i.e., solvent exchange events. Ultrafast two-dimensional (2D) IR spectroscopy can probe exchange processes directly via the evolution of the cross-peaks on picosecond time scales. However, vibrational energy transfer in the absence of solvent exchange gives rise to the same spectral signatures, hiding the desired processes. Here we employ 2D IR on solvent resonances of a mixture of acetonitrile isotopologues to differentiate chemical exchange and energy-transfer dynamics in a comprehensive series of Li + , Mg 2+ , Zn 2+ , Ca 2+ , and Ba 2+ bis(trifluoromethylsulfonyl)imide electrolytes from the dilute to the superconcentrated regime. No exchange phenomena occur within at least 100 ps, regardless of the ion identity, salt concentration, and presence of water. All of the observed spectral dynamics originate from the intermolecular energy transfer. These results place the lower experimental boundary on the ion–solvent residence times to several hundred picoseconds, much slower than previously suggested. With the help of MD simulations and conductivity measurements on the Li + and Zn 2+ systems, we discuss these results as a continuum of vehicular and structural modalities that vary with concentration and emphasize the importance of collective electrolyte motions to ion transport. These results hold broadly applicable to many battery-relevant ions and solvents.

25 ENERGY STORAGE↗