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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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Mergers of Black-Hole Binaries with Aligned Spins: Waveform Characteristics

"We apply our gravitational-waveform analysis techniques, first presented in the context of nonspinning black holes of varying mass ratio [1], to the complementary case of equal-mass spinning black-hole binary systems. We find that, as with the nonspinning mergers, the dominant waveform modes phases evolve together in lock-step through inspiral and merger, supporting the previous model of the binary system as an adiabatically rigid rotator driving gravitational-wave emission - an implicit rotating source (IRS). We further apply the late-merger model for the rotational frequency introduced in [1], along with a new mode amplitude model appropriate for the dominant (2, plus or minus 2) modes. We demonstrate that this seven-parameter model performs well in matches with the original numerical waveform for system masses above - 150 solar mass, both when the parameters are freely fit, and when they are almost completely constrained by physical considerations."

Kelly, Bernard J.↗
NASA NTRSDate not supplied

Quasi-Wide-Band Laser

Quasi-Wide-Band (QWB) laser is first-time presented, whose gain-line-shape depends on the frequency-shift and line-broadening caused by temperature gradient and others. The self-mode-locking, ultra-low phase-noise amplification, and coherent beam combination of QWB laser are investigated.

Yingxin Bai↗
DOE OSTI2015

Formation mechanism of steep wave front in magnetized plasmas

Bifurcation from a streamer to a solitary drift wave is obtained in three dimensional simulation of resistive drift waves in cylindrical plasmas. The solitary drift wave is observed in the regime where the collisional transport is important as well as fluctuation induced transport. The solitary drift wave forms a steep wave front in the azimuthal direction. The phase of higher harmonic modes are locked to that of the fundamental mode, so that the steep wave front is sustained for a long time compared to the typical time scale of the drift wave oscillation. The phase entrainment between the fundamental and second harmonic modes is studied, and the azimuthal structure of the stationary solution is found to be characterized by a parameter which is determined by the deviation of the fluctuations from the Boltzmann relation. There are two solutions of the azimuthal structures, which have steep wave front facing forward and backward in the wave propagation direction, respectively. The selection criterion of these solutions is derived theoretically from the stability of the phase entrainment. The simulation result and experimental observations are found to be consistent with the theoretical prediction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

An efficient magnetron transmitter for superconducting accelerators

A concept of a highly-efficient high-power magnetron transmitter allowing wide-band phase and the mid-frequency power control at the frequency of the locking signal is proposed. The proposal is aimed for powering Superconducting RF (SRF) cavities of intensity-frontier accelerators. The transmitter is intended to operate with phase and amplitude control feedback loops allowing suppression of microphonics and beam loading in the SRF cavities. The concept utilizes injectionlocked magnetrons controlled in phase by the locking signal supplied by a feedback system. The injection-locking signal pre-excites the magnetron and allows its operation below the critical voltage. This realizes control of the magnetron power in a wide range by control of the magnetron current. Pre-excitation of the magnetron by the locking signal provides an output power range up to 10 dB. Experimental studies were carried out with 2.45 GHz, 1 kW, CW magnetrons. They demonstrated stable operation of the magnetrons and power control at a low noise level. In conclusion, an analysis of the kinetics of the drifting charge in the drift approximation substantiates the concept and the experimental results.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Helical Edge States and Quantum Phase Transitions in Tetralayer Graphene

Helical conductors with spin-momentum locking are promising platforms for Majorana fermions. Here we report observation of two topologically distinct phases supporting helical edge states in charge neutral Bernal-stacked tetralayer graphene in Hall bar and Corbino geometries. As the magnetic field B ⊥ and out-of-plane displacement field D are varied, we observe a phase diagram consisting of an insulating phase and two metallic phases, with 0, 1, and 2 helical edge states, respectively. These phases are accounted for by a theoretical model that relates their conductance to spin-polarization plateaus. Transitions between them arise from a competition among interlayer hopping, electrostatic and exchange interaction energies. Finally, our work highlights the complex competing symmetries and the rich quantum phases in few-layer graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Longitudinal phase space manipulation of an ultrashort electron beam via THz IFEL interaction

A scheme where a laser locked THz source is used to manipulate the longitudinal phase space of an ultrashort electron beam using an IFEL interaction is investigated. The efficiency of THz source based on the pulse front tilt optical rectification scheme is increased by cryogenic cooling to achieve sufficient THz power for compression and synchronization. Start-to-end simulations describing the evolution of the beam from the cathode to the compression point after the undulator are presented.

43 PARTICLE ACCELERATORS↗
NASA NTRS2011

System and method for tuning adjusting the central frequency of a laser while maintaining frequency stabilization to an external reference

A method and system for stabilizing a laser to a frequency reference with an adjustable offset. The method locks a sideband signal generated by passing an incoming laser beam through the phase modulator to a frequency reference, and adjusts a carrier frequency relative to the locked sideband signal by changing a phase modulation frequency input to the phase modulator. The sideband signal can be a single sideband (SSB), dual sideband (DSB), or an electronic sideband (ESB) signal. Two separate electro-optic modulators can produce the DSB signal. The two electro-optic modulators can be a broadband modulator and a resonant modulator. With a DSB signal, the method can introduce two sinusoidal phase modulations at the phase modulator. With ESB signals, the method can further drive the optical phase modulator with an electrical signal with nominal frequency OMEGA(sub 1) that is phase modulated at a frequency OMEGA(sub 2)

Livas, Jeffrey↗
DOE OSTI2020

Backscatter-Immune Injection-Locked Brillouin Laser in Silicon

As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser’s frequency and phase can be controlled by an injected signal. Because of its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection-locking dynamics remain relatively untapped—despite significant potential for technological and scientific impact. In this work, we demonstrate injection locking in a silicon photonic Brillouin laser. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the Brillouin gain bandwidth. Harnessing these dynamics, we demonstrate amplification of small signals by more than 23 dB. Moreover, we demonstrate that the injection-locking dynamics of this system are inherently nonreciprocal, yielding unidirectional control and backscatter immunity in an all-silicon system. This device physics opens the door to strategies for phase-noise reduction, low-noise amplification, and backscatter immunity in silicon photonics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Bulk-SQUID effect in a discrete superconductor as a consequence of generation frequency locking in constituent josephson junctions

The theory of the bulk-SQUID effect in discrete superconductors is constructed for the first time. It is shown that the bulk-SQUID effect emerges in the system of 2D intrinsically stochastic multijunction SQUID (i.e., with random values of critical currents of the junctions, injection currents, and the coupling coefficients between the junction) due to generation frequency locking in all junctions. It is demonstrated that the bulk-SQUID effect occurs in a wide range of random parameters of the system. This domain of variation of the system parameters can be divided into three subdomains. The first one is the subdomain of coherent dynamics of phases at the junctions, the second is the subdomain of incoherent dynamics, in which the phases of the junctions are not locked, but the bulk-SQUID effect persists, and the third is the subdomain of transient dynamics, in which coherent dynamics and the bulk-SQUID effect are observed in parts. A simple mathematical model of noninteracting junctions, which correctly describes basic features of the dynamics of the initial system and makes it possible to calculate some of its statistical characteristics, is proposed and analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Delay-locked-loop timing error mitigation

Systems, methods, and circuits provide delay-locked loop (DLL) timing error mitigation. A DLL false-lock detection system can include DLL circuitry configured to receive a reference clock signal having a time period. The system can include shift register circuitry and latched comparison circuitry which can determine a time period of a locked condition of the DLL delay line with respect to the reference clock signal time period. The system can determine whether the system is correctly locked to the base time period or incorrectly locked to a multiple of the base time period. A further system can operate to cause a phase detector circuitry in a DLL to ignore the first edge of a reference clock signal presented to the phase detector circuitry and thereby avoid stuck-lock conditions.

Filippini, Leo↗
NASA NTRS2010

Optimization of A 2-Micron Laser Frequency Stabilization System for a Double-Pulse CO2 Differential Absorption Lidar

A carbon dioxide (CO2) Differential Absorption Lidar (DIAL) for accurate CO2 concentration measurement requires a frequency locking system to achieve high frequency locking precision and stability. We describe the frequency locking system utilizing Frequency Modulation (FM), Phase Sensitive Detection (PSD), and Proportional Integration Derivative (PID) feedback servo loop, and report the optimization of the sensitivity of the system for the feed back loop based on the characteristics of a variable path-length CO2 gas cell. The CO2 gas cell is characterized with HITRAN database (2004). The method can be applied for any other frequency locking systems referring to gas absorption line.

Chen, Songsheng↗
NASA NTRS1987

Response of a Fabry-Perot cavity to phase modulated light

A solution to the lock-in detection method, which is valid for arbitrary values of the modulation frequency, is described. The theory for determining frequency modulation of a single frequency laser is presented. The theoretical predictions for the optimum modulation index are compared to experimental solutions for the quasi-static regime. Signal line shapes for first, second, and third harmonic generations are derived and examined. It is noted that there is good correlation between experimental and quasi-static theory data for the relation between small modulation frequency and resonance linewidth.

Hils, Dieter↗
DOE OSTI2023

Offset lock with a 440-GHz range using electro-optic modulation

Offset locking is crucial to many physics experiments. Wide range offset locks are desirable, as they increase the span of usable frequencies in an experiment. Here, we experimentally realize a wide-range offset lock using a beat-note setup combined with electro-optic phase modulation. By using frequency down-conversion of the beat note and locking to sidebands generated by electro-optic modulation, we achieve an offset range of ± 220.1 GHz with offset frequency fluctuations under 0.1 Hz and a phase error variance of 0.017 rad 2 over a 100 kHz bandwidth, greatly widening the range compared to past setups using this method. The relative simplicity of our setup provides a compelling method for locking at offsets in the hundreds of GHz range.

Zhou, Ocean (ORCID:0000000279192636)↗
DOE OSTI2023

Ultrafast Laser Pulse Generation by Mode Locking: MATLAB-Based Demonstrations

Ultrafast laser spectroscopy is a valuable and increasingly accessible technique for studies of rapid chemical reactions. Critical to ultrafast spectroscopy is the concept of mode locking, a technique that enables a fixed phase relationship between laser modes, resulting in laser pulses with very short duration (in the fs or ps range). Despite the increasing importance of ultrafast lasers in chemistry, the introduction of key concepts behind their operation into the undergraduate and graduate chemistry coursework has been limited. To help the incorporation of these topics into chemistry courses, we report here a hands-on activity that helps students develop an intuitive understanding of the factors that impact electromagnetic wave evolution in optical cavities and the process of mode locking. We first provide the theoretical background by introducing cavity modes and contrasting them with well-known propagating electromagnetic waves. We then explore what happens when modes are added and how the relative phase between the modes affects their behavior. In the second section of this report, three teaching modules are provided, along with associated MATLAB codes and animated images, that can be used in the classroom to introduce concepts of cavity modes and mode locking. These teaching modules start by contrasting propagating electromagnetic waves with cavity modes and then illustrate what happens when multiple modes are present in the cavity and how the relative phase between the modes affects the overall electromagnetic field in the cavity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗