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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Preparing for successful protein crystallization experiments

Crystal-based structural methods, including X-ray crystallography, are frequently utilized for the determination of high-resolution structures of biomolecules. All crystal-based diffraction methods first require the preparation of biomolecular crystals, and careful sample preparation for crystallization experiments can increase the frequency of success. In this article, strategies to optimize factors that can impact crystallization are presented, from which buffers and reducing agents are most favorable to which crystallization techniques could be used.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Macromolecular phasing using diffraction from multiple crystal forms

A phasing algorithm for macromolecular crystallography is proposed that utilizes diffraction data from multiple crystal forms – crystals of the same molecule with different unit-cell packings (different unit-cell parameters or space-group symmetries). The approach is based on the method of iterated projections, starting with no initial phase information. The practicality of the method is demonstrated by simulation using known structures that exist in multiple crystal forms, assuming some information on the molecular envelope and positional relationships between the molecules in the different unit cells. With incorporation of new or existing methods for determination of these parameters, the approach has potential as a method for ab initio phasing.

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

Perspectives on UV and x-ray photoelectron spectroscopy

Atomic photoionization using electron spectroscopy was one of the scientific topics in which Professor David A. Shirley excelled and established a research legacy. We discuss selected highlights of atomic photoionization research done by the Shirley group beginning in the 1970s. Our main topics are electron correlation satellites, photoelectron angular distributions with tunable synchrotron radiation, and developments of theory. We also discuss examples of more recent research that extends the earlier work, including double K-shell photoionization, nondipole interactions, and the pervasive role of interchannel coupling. Furthermore, we conclude with examples of current experimental and theoretical research.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Ultrafast X-Ray Probes of Elementary Molecular Events

Elementary events that determine photochemical outcomes and molecular functionalities happen on the femtosecond and subfemtosecond timescales. Among the most ubiquitous events are the nonadiabatic dynamics taking place at conical intersections. These facilitate ultrafast, nonradiative transitions between electronic states in molecules that can outcompete slower relaxation mechanisms such as fluorescence. The rise of ultrafast X-ray sources, which provide intense light pulses with ever-shorter durations and larger observation bandwidths, has fundamentally revolutionized our spectroscopic capabilities to detect conical intersections. Recent theoretical studies have demonstrated an entirely new signature emerging once a molecule traverses a conical intersection, giving detailed insights into the coupled nuclear and electronic motions that underlie, facilitate, and ultimately determine the ultrafast molecular dynamics. Following a summary of current sources and experiments, we survey these techniques and provide a unified overview of their capabilities. We discuss their potential to dramatically increase our understanding of ultrafast photochemistry.

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

LCLS RF Station Anomaly Candidates, SLAC, Nov 2020 to Dec 2020, Version 1

The data consists of radio-frequency (RF) station process variables (amplitude and amplitude-mean-out-of-tolerance bit) and beam position monitor (BPM) values for about a month of Linac Coherent Light Source (LCLS) time. The data is all from normal conducting hard X-ray operation. The dataset contains roughly 5000 anomaly “candidates.” For each candidate, we include 3.5 minutes of data from the 82 RF stations and ~20 seconds of data from 4 BPMs. We also include several CSV files with additional information and labels for each candidate.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

X-ray pulse generation with ultra-fast flipping of its orbital angular momentum

A method to temporally tailor the properties of X-ray radiation carrying Orbital Angular Momentum (OAM) is presented. In simulations, an electron beam is prepared with a temporally modulated micro-bunching structure which, when radiating at the second harmonic in a helical undulator, generates OAM light with a corresponding temporally modulated intensity. This method is shown to generate attosecond pulse trains of OAM light without the need for any additional external optics, making the wavelength range tunable. In addition to the OAM pulse train, the method can be adapted to generate radiation where the handedness of the OAM mode may also be temporally modulated (flipped).

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Data reduction through optimized scalar quantization for more compact neural networks

Raw data generation for several existing and planned large physics experiments now exceeds TB/s rates, generating untenable data sets in very little time. Those data often demonstrate high dimensionality while containing limited information. Meanwhile, Machine Learning algorithms are now becoming an essential part of data processing and data analysis. Those algorithms can be used offline for post processing and post data analysis, or they can be used online for real time processing providing ultra low latency experiment monitoring. Both use cases would benefit from data throughput reduction while preserving relevant information: one by reducing the offline storage requirements by several orders of magnitude and the other by allowing ultra fast online inferencing with low complexity Machine Learning models. Moreover, reducing the data source throughput also reduces material cost, power and data management requirements. In this work we demonstrate optimized nonuniform scalar quantization for data source reduction. This data reduction allows lower dimensional representations while preserving the relevant information of the data, thus enabling high accuracy Tiny Machine Learning classifier models for online fast inferences. We demonstrate this approach with an initial proof of concept targeting the CookieBox, an array of electron spectrometers used for angular streaking, that was developed for LCLS-II as an online beam diagnostic tool. We used the Lloyd-Max algorithm with the CookieBox dataset to design an optimized nonuniform scalar quantizer. Optimized quantization lets us reduce input data volume by 69% with no significant impact on inference accuracy. When we tolerate a 2% loss on inference accuracy, we achieved 81% of input data reduction. Finally, the change from a 7-bit to a 3-bit input data quantization reduces our neural network size by 38%.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1989

Technical options for high average power free electron milimeter-wave and laser devices

Many of the potential space power beaming applications require the generation of directed energy beams with respectable amounts of average power (MWs). A tutorial summary is provided here on recent advances in the laboratory aimed at producing direct conversion of electrical energy to electromagnetic radiation over a wide spectral regime from microwaves to the ultraviolet.

Swingle, James C.↗
NASA NTRS1994

Fabrication and Testing of a Large Primary Reflector Structure

This paper discusses the fabrication considerations and proposed testing concepts related to a large twelve meter, graphite-epoxy space truss that is being developed to provide support of the primary mirror system for the Beam Transmission Optical System (BTOS).

space truss primary reflector free electron laser ↗
DOE OSTI2024

Nozzle-Free Printing of CNT Electronics Using Laser-Generated Focused Ultrasound

Printed electronics have made remarkable progress in recent years and inkjet printing (IJP) has emerged as one of the leading methods for fabricating printed electronic devices. However, challenges such as nozzle clogging, and strict ink formulation constraints have limited their widespread use. To address this issue, a novel nozzle-free printing technology is explored, which is enabled by laser-generated focused ultrasound, as a potential alternative printing modality called Shock-wave Jet Printing (SJP). Specifically, the performance of SJP-printed and IJP-printed bottom-gated carbon nanotube (CNT) thin film transistors (TFTs) is compared. While IJP required ten print passes to achieve fully functional devices with channel dimensions ranging from tens to hundreds of micrometers, SJP achieved comparable performance with just a single pass. For optimized devices, SJP demonstrated six times higher maximum mobility than IJP-printed devices. Furthermore, the advantages of nozzle-free printing are evident, as SJP successfully printed stored and unsonicated inks, delivering moderate electrical performance, whereas IJP suffered from nozzle clogging due to CNT agglomeration. Moreover, SJP can print significantly longer CNTs, spanning the entire range of tube lengths of commercially available CNT ink. The findings from this study contribute to the advancement of nanomaterial printing, ink formulation, and the development of cost-effective printable electronics.

47 OTHER INSTRUMENTATION↗
NASA NTRS2010

Free-Free Transitions in the Presence of Laser Fields at Very Low Incident Electron Energy

We study the free-free transition in electron-hydrogenic systems in ground state in presence of an external laser field at very loud incident energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen to be monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser in a nonperturbative manner by choosing a Volkov wave function for it. The scattering weave function for the electron is solved numerically by taking into account the effect of the electron exchange, short-range as well as of the long-range interactions to get the S and P wave phase shifts while for the higher angular momentum phase shifts the exchange approximation has only been considered. We calculate the laser assisted differential cross sections (LADCS) for the aforesaid free-free transition process for single photon absorption/emission. The laser intensity is chosen to be much less than the atomic field intensity. A strong suppression is noted in the LADCS as compared to the field free (FF) cross sections. Unlike the FF ones, the LADCS exhibit some oscillations having a distinct maximum at a low value of the scattering angle depending on the laser parameters as well as on the incident energies.

Bhatia, A. K.↗
NASA NTRS2009

Free-Free Transitions in the Presence of Laser Fields at Very Low Incident Electron Energy

We study the free-free transition in electron-hydrogenic systems in ground state in presence of an external laser field at very low incident energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen to be monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser in a nonperturbative manner by choosing a Volkov wave function for it The scattering wave function for the electron is solved numerically by taking into account the effect of the electron exchange, short-range as well as of the long-range interactions to get the S and P wave phase shifts while for the higher angular momentum phase shifts, the exchange approximation has only been considered. We calculate the laser-assisted differential cross sections (LADCS) for the aforesaid free-free transition process for single photon absorption/emission. The laser intensity is chosen to be much less than the atomic field intensity. A strong suppression is noted in the LADCS as compared to the field free (FF) cross sections. Unlike the FF ones, the LADCS exhibit some oscillations having a distinct maximum at a low value of the scattering angle depending on the laser parameters as well as on the incident energies.

Bhatia, Anand K.↗
DOE OSTI2023

Toward direct spatial and intensity characterization of ultra-high-intensity laser pulses using ponderomotive scattering of free electrons

Spatial distributions of electrons ionized and scattered from ultra-low-pressure gases are proposed and experimentally demonstrated as a method to directly measure the intensity of an ultra-high-intensity laser pulse. Analytic models relating the peak scattered electron energy to the peak laser intensity are derived and compared to paraxial Runge–Kutta simulations highlighting two models suitable for describing electrons scattered from weakly paraxial beams (f#>5) for intensities in the range of 1018−1021 W cm−2. Scattering energies are shown to be dependent on gas species, emphasizing the need for specific gases for given intensity ranges. Direct measurements of the laser intensity at full power of two laser systems are demonstrated, both showing a good agreement between indirect methods of intensity measurement and the proposed method. One experiment exhibited the role of spatial aberrations in the scattered electron distribution, motivating a qualitative study on the effect. We propose the use of convolutional neural networks as a method for extracting quantitative information on the spatial structure of the laser at full power. We believe the presented technique to be a powerful tool that can be immediately implemented in many high-power laser facilities worldwide.

47 OTHER INSTRUMENTATION↗
NASA NTRS2017

Mixture-Fraction Measurements with Femtosecond-Laser Electronic-Excitation Tagging

Tracer-free mixture-fraction measurements were demonstrated in a jet using femtosecond-laser electronic-excitation tagging. Measurements were conducted across a turbulent jet at several downstream locations both in a pure-nitrogen jet exiting into an air-nitrogen mixture and in a jet containing an air-nitrogen mixture exiting into pure nitrogen. The signal was calibrated with known concentrations of oxygen in nitrogen. The spatial resolution of the measurement was approx.180 microns. The measurement uncertainty ranged from 5% to 15%, depending on the mixture fraction and location within the beam, under constant temperature and pressure conditions. The measurements agree with a mixture fraction of unity within the potential core of the jet and transition to the self-similar region.

Halls, Benjamin R.↗
NASA NTRS2012

Free-Free Transitions in the Presence of Laser Fields and Debye Potential at Very Low Incident Electron Energies

We study the free-free transition in electron-helium ion in the ground state and embedded in a Debye potential in the presence of an external laser field at very low incident electron energies. The laser field is treated classically while the collision dynamics is treated quantum mechanically. The laser field is chosen as monochromatic, linearly polarized and homogeneous. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing Volkov wave function for it. The scattering wave function for the incident electron on the target embedded in a Debye potential is solved numerically by taking into account the effect of electron exchange. We calculate the laser-assisted differential and total cross sections for free-free transition for absorption/emission of a single photon or no photon exchange. The results will be presented at the conference.

Bhatia, Anand↗
NASA NTRS1981

Plasma lasers (a strong source of coherent radiation in astrophysics)

The generation of electromagnetic radiation from the free energy available in electron streams is discussed. The fundamental principles involved in a particular class of coherent plasma radiation sources, i.e., plasma lasers, are reviewed, focusing on three wave coupling, nonlinear parametric instabilities, and negative energy waves. The simplest case of plasma lasers, that of an unmagnetized plasma containing a finite level of density fluctuations and electrons streaming with respect to the ions, is dealt with. A much more complicated application of plasma lasers to the case of auroral kilometric radiation is then examined. The concept of free electron lasers, including the role of relativistic scattering, is elucidated. Important problems involving the escape of the excited radiation from its generation region, effects due to plasma shielding and nonlinear limits, are brought out.

Papadopoulos, K.↗
NASA NTRS1992

Electronic Subsystems For Laser Communication System

Electronic subsystems of free-space laser communication system carry digital signals at 650 Mb/s over long distances. Applicable to general optical communications involving transfer of great quantities of data, and transmission and reception of video images of high definition.

Long, Catherine↗