Single-Frequency Light from an Argon FM Laser
Single frequency light from argon FM laser with external lithium niobate modulator, discussing overall conversion efficiency and distortion reduction
OPTICAL POWER LIMITER↗
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Results for “FREQUENCY MODULATION”
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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Measurement of Relaxation Time of Excess Carriers in Si and CIGS Solar Cells by Modulated Electroluminescence Technique
Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment. For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps.
14 SOLAR ENERGY↗
Characterization of high-frequency waves in the Martian magnetosphere
Context.Various high-frequency waves in the vicinity of upper-hybrid and Langmuir frequencies are commonly observed in different space plasma environments. Such waves and fluctuations have been reported in the magnetosphere of the Earth, a planet with an intrinsic strong magnetic field. Mars has no intrinsic magnetic field and, instead, it possesses a weak induced magnetosphere, which is highly dynamic due to direct exposure to the solar wind. In the present paper, we investigate the presence of high-frequency plasma waves in the Martian plasma environment by making use of the high-resolution electric field data from the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft. Aims.This study aims to provide conclusive observational evidence of the occurrence of high-frequency plasma waves around the electron plasma frequency in the Martian magnetosphere. We observe two distinct wave modes with frequency below and above the electron plasma frequency. The characteristics of these high-frequency waves are quantified and presented here. We discuss the generation of possible wave modes by taking into account the ambient plasma parameters in the region of observation. Methods.We have made use of the medium frequency (100 Hz–32 kHz) burst mode-calibrated electric field data from the Langmuir Probe and Waves instrument on board NASA’s MAVEN mission. Due to the weak magnetic field strength, the electron gyro-frequency is much lower than the electron plasma frequency, which implies that the upper-hybrid and Langmuir waves have comparable frequencies. A total of 19 wave events with wave activities around electron plasma frequency were identified by examining high-resolution spectrograms of the electric field. Results.These waves were observed around 5 LT when MAVEN crossed the magnetopause boundary and entered the magnetosheath region. These waves are either a broadband- or narrowband-type with distinguishable features in the frequency domain. The narrowband-type waves have spectral peak above the electron plasma frequency. However, in the case of broadband-type waves, the spectral peak always occurred below the electron plasma frequency. The broadband waves consistently show a periodic modulation of 8–14 ms. Conclusions.The high-frequency narrowband-type waves observed above the electron plasma frequency are believed to be associated with upper-hybrid or Langmuir waves. However, the physical mechanism responsible for the generation of broadband-type waves and the associated 8–14 ms modulation remain unexplained and further investigation is required.
Astronomy & Astrophysics↗
Sizing SiC Storage Inverters for Fast Grid Frequency Support
As wind and solar displace synchronous generators whose inertia stabilizes the AC grid frequency on fast time scales, it has been proposed to use energy storage systems (ESSs) to mitigate frequency transient events. Such events require a rapid surge of power from the ESS, but they occur only rarely. The high temperature tolerance of SiC MOSFETs and diodes presents an opportunity for innovative ESS inverter designs. Herein we investigate a SiC ESS inverter design such that the SiC device ratings are obeyed during mild frequency events but are exceeded during rare, major events, for a potentially more economical inverter design. In support of this proposal we present: 1. An analysis of four years of grid frequency events in the U.S. Western Interconnection. 2. A switch-level ESS inverter simulation using SiC devices with detailed loss estimates. 3. Thermal analysis of the SiC power modules during a worst-case frequency event, showing that the modules can likely withstand the brief overcurrent. This analysis supports the conclusion that it may be advantageous for economical designs (acknowledging the increased risks) to undersize the SiC switches when designing inverters to perform active power control for grid frequency support. Such a strategy may result in SiC-based designs being more competitive with less costly silicon IGBT-based designs.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Preliminary results of the on-demand vortex-generator experiments
This is a report on the continuation of our experimental investigations (Saddoughi 1994) of 'on-demand' vortex generators. Conventional vortex generators as found on aircraft wings are mainly for suppression of separation during the off-design conditions. In cruise they perform no useful function and exert a significant drag penalty. Therefore, replacement of fixed rectangular or delta-wing generators by devices that could be activated when needed would be of interest. Also in our previous report, we described one example of an 'on-demand' device, which was developed by Jacobson & Reynolds (1995) at Stanford University, suitable for manufacture by micro-electro-mechanical technology. This device consists of a surface cavity elongated in the stream direction and covered with a lid cantilevered at the upstream end. The lid, which is a metal sheet with a sheet of piezoelectric ceramic bonded to it, lies flush with the boundary. On application of a voltage the ceramic expands or contracts; however, adequate amplitude can be obtained only by running at the cantilever resonance frequency and applying amplitude modulation: for 2.5 mm x 20 mm cantilevered lids, they obtained maximum tip displacements of the order of 100 pm. Thus fluid is expelled from the cavity through the gap around the lid on the downstroke. They used an asymmetrical gap configuration and found that periodic emerging jets on the narrow side induced periodic longitudinal vorticity into the boundary layer. Their device was used to modify the inner layer of the boundary layer for skin-friction reduction. The same method could be implemented for the replacement of the conventional vortex generators; however, to promote mixing and suppress separation we needed to deposit longitudinal vortices into the outer layer of the boundary layer, which required a larger vortex generator than the device built by Jacobson & Reynolds. Our vortex generator was built with a mechanically-driven cantilevered lid with an adjustable frequency. The device was made about ten times the size of Jacobson & Reynolds', the shape or size of the cavity and lid (28 mm x 250 mm) could be easily changed. The cavity depth, the cantilever-tip displacement, and the maximum lid frequency were 20 mm, 10 mm, and 60 Hz respectively. Our vortex generator was mounted on a turntable so that its yaw angle could be changed. Finally, tests over a range of ratios of vortex generator size to boundary-layer thickness could be carried out simply by changing the streamwise location of the device.
Saddoughi, Seyed G.↗
Digital Distortion Caused by Traveling- Wave-Tube Amplifiers Simulated
Future NASA missions demand increased data rates in satellite communications for near real-time transmission of large volumes of remote data. Increased data rates necessitate higher order digital modulation schemes and larger system bandwidth, which place stricter requirements on the allowable distortion caused by the high-power amplifier, or the traveling-wave-tube amplifier (TWTA). In particular, intersymbol interference caused by the TWTA becomes a major consideration for accurate data detection at the receiver. Experimentally investigating the effects of the physical TWTA on intersymbol interference would be prohibitively expensive, as it would require manufacturing numerous amplifiers in addition to acquiring the required digital hardware. Thus, an accurate computational model is essential to predict the effects of the TWTA on system-level performance when a communication system is being designed with adequate digital integrity for high data rates. A fully three-dimensional, time-dependent, TWT interaction model has been developed using the electromagnetic particle-in-cell code MAFIA (Solution of Maxwell's equations by the Finite-Integration-Algorithm). It comprehensively takes into account the effects of frequency-dependent AM (amplitude modulation)/AM and AM/PM (phase modulation) conversion, gain and phase ripple due to reflections, drive-induced oscillations, harmonic generation, intermodulation products, and backward waves. This physics-based TWT model can be used to give a direct description of the effects of the nonlinear TWT on the operational signal as a function of the physical device. Users can define arbitrary excitation functions so that higher order modulated digital signals can be used as input and that computations can directly correlate intersymbol interference with TWT parameters. Standard practice involves using communication-system-level software packages, such as SPW, to predict if adequate signal detection will be achieved. These models use a nonlinear, black-box model to represent the TWTA. The models vary in complexity, but most make several assumptions regarding the operation of the high-power amplifier. When the MAFIA TWT interaction model was used, these assumptions were found to be in significant error. In addition, digital signal performance, including intersymbol interference, was compared using direct data input into the MAFIA model and using the system-level analysis tool SPW for several higher order modulation schemes. Results show significant differences in predicted degradation between SPW and MAFIA simulations, demonstrating the significance of the TWTA approximations made in the SPW model on digital signal performance. For example, a comparison of the SPW and MAFIA output constellation diagrams for a 16-ary quadrature amplitude modulation (16-QAM) signal (data shown only for second and fourth quadrants) is shown. The upper-bound degradation was calculated from the corresponding eye diagrams. In comparison to SPW simulations, the MAFIA data resulted in a 3.6-dB larger degradation.
Kory, Carol L.↗
Spin and mass of the supermassive black hole in the Galactic Center
A new method for exact determination of the masses and spins of black holes from the observations of quasi-periodic oscillations is discussed. The detected signal from the hot clumps in the accretion plasma must contain modulations with two characteristic frequencies: the frequency of rotation of the black hole event horizon and the frequency of the latitudinal precession of the clump’s orbit. Application of the method of two characteristic frequencies for interpretation of the observed quasi-periodic oscillations from the supermassive black hole in the Galactic center in the X-rays and in the near IR region yields the most exact, for the present, values of the mass and the spin (Kerr parameter) of the Sgr A* black hole: M = (4.2 ± 0.2) × 10{sup 6}M{sub ⊙} and a = 0.65 ± 0.05. The observed quasi-periodic oscillations with a period of about 11.5 min are identified as the black hole event horizon rotation period and those with a period of about 19 min are identified as the latitudinal oscillation period of the hot spot orbits in the accretion disk.
79 ASTRONOMY AND ASTROPHYSICS↗
Bell state analyzer for spectrally distinct photons
We demonstrate a Bell state analyzer that operates directly on frequency mismatch. Based on electro-optic modulators and Fourier-transform pulse shapers, our quantum frequency processor design implements interleaved Hadamard gates in discrete frequency modes. Experimental tests on entangled-photon inputs reveal fidelities of ∼ <#comment/> 98 % <#comment/> for discriminating between the | Ψ <#comment/> + ⟩ <#comment/> and | Ψ <#comment/> − <#comment/> ⟩ <#comment/> frequency-bin Bell states. Our approach resolves the tension between wavelength-multiplexed state transport and high-fidelity Bell state measurements, which typically require spectral indistinguishability.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Dynamics of the magnetic shearing instability and magnetohydrodynamic turbulence in accretion disks. 1: Vertical magnetic field
Recently, the magnetic shearing instability (MSI) has been proposed as a dynamical mechanism for angular momentum transport in accretion disks (Balbus & Hawley 1991; Hawley & Balbus 1991). In this paper, the nonlinear dynamics of MSI modes in the presence of a vertical magnetic field B(sub 0) is discussed. In particular, the saturation levels of the fluctuating fields, the angular momentum flux, and the energy dissipation mechanism, are examined in detail. It is shown that MSI induces strong magnetohydrodynamic (MHD) turbulence in a range of wavenumbers 1/H is less than K is less than or equal to Omega/V(sub A)(sub 0)), where H is the thickness, Omega is the rotation frequency of the disk, and V(sub A)(sub 0) is the Alfven velocity. Despite the fact that the linear growth rate of MSI is maximal at small-scale (i.e., k is approximately Omega/V(sub A(sub 0)), angular momentum transport due to MSI turbulence is dominated by the magnetic Reynolds stress driven by large-scale modes (k is approximately 1/H). It is shown that the amplitude of low k(sub r) MSI eddies is limited primarily by subscale shear flow instability. Thus, dominant MSI cells are quasi-isotropic. In a stationary state, the effective Shakura-Sunyaev 'alpha' value is predicted to be of order V(sub A)(sub 0)0/C(sub s). In addition, the veritcal magnetic-field-induced MSI cells convert vertical magnetic field B(sub 0) into azimuthal magnetic field B(sub theta) in the disk. The generation of azimuthal magnetic field in turn introduces new physical processes, such as dynamo activity and azimuthal MSI turbulence. We conclude that it is not possible to decouple vertical MSI saturation from azimuthal MSI evolution. Low-frequency MSI cells are shown to co-exist with high-frequency radial buoyancy or internal waves. We show that modulational interaction between waves on these two frequency ranges is usually weak in the case when mean magnetic field is vertical. Thus, MSI and internal wave dynamics must be treated on an equal footing.
Zhang, W.↗
Model of a laser gyroscope with frequency dithering
The model of a laser gyroscope (LG) with frequency dithering is described by a system of recurrent equations for the electric fields of counterpropagating waves. The phenomenon of frequency locking is taken into account in the form of the wave coupling through backward scattering; the frequency bias factor is the controlled phase nonreciprocity. The character of the output signal is considered, which corresponds to two types of frequency dithering, namely, sinusoidal and in the form of meander that are produced by various methods, including intracavity phase modulation. Results of calculation of a frequency characteristic of the LG are presented as functions of frequency dithering, rotational velocity and LG parameters. It is shown that the method of processing an output signal by measuring the time interval between intensity oscillations has an advantage due to the absence of so-called dynamic lock-in zones in the output characteristic. (laser gyroscope)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Dual-Photoelastic-Modulator-Based Polarimetric Imaging Concept for Aerosol Remote Sensing
A dual-photoelastic-modulator- (PEM-) based spectropolarimetric camera concept is presented as an approach for global aerosol monitoring from space. The most challenging performance objective is to measure degree of linear polarization (DOLP) with an uncertainty of less than 0.5% in multiple spectral bands, at moderately high spatial resolution, over a wide field of view, and for the duration of a multiyear mission. To achieve this, the tandem PEMs are operated as an electro-optic circular retardance modulator within a high-performance reflective imaging system. Operating the PEMs at slightly different resonant frequencies generates a beat signal that modulates the polarized component of the incident light at a much lower heterodyne frequency. The Stokes parameter ratio q = Q/I is obtained from measurements acquired from each pixel during a single frame, providing insensitivity to pixel responsivity drift and minimizing polarization artifacts that conventionally arise when this quantity is derived from differences in the signals from separate detectors. Similarly, u = U/I is obtained from a different pixel; q and u are then combined to form the DOLP. A detailed accuracy and tolerance analysis for this polarimeter is presented.
spectropolarimetric imaging↗
On the Regionality of Moist Kelvin Waves and the MJO: The Critical Role of the Background Zonal Flow
Abstract A global model with superparameterized physics is used to shed light on the observed regionality of convectively coupled Kelvin waves and the Madden‐Julian Oscillation (MJO). A series of aquaplanet simulations over zonally uniform sea‐surface temperatures is performed, in which the axisymmetric structure of the background zonal flow is altered through nudging, while maintaining a quasi‐fixed rainfall climatology. Results show that nudging at the equator to match profiles typical of the Indo‐Pacific or eastern Pacific sectors yields eastward‐moving tropical rain spectra typical of those sectors. Two different mechanistic pathways are identified as being responsible for this mean‐flow dependence, in addition to Doppler shifting effects. The first is through shifts of the Rossby wave critical line in the subtropical upper troposphere that affect the lateral forcing of Kelvin‐mode circulations at the equator by eastward and equatorward‐propagating eddies impinging on the tropics from higher latitudes. The second is through changes in the strength of the mean cyclonic shear in the lower tropical troposphere that affect the degree to which intraseasonal fluctuations in Kelvin‐mode zonal winds modulate the activity of higher‐frequency equatorial Rossby‐type eddies. In cases where the mean low‐level cyclonic shear is enhanced, the strength of this modulation, referred to as “shear‐induced eddy modulation” or SIEM, is also seen to be enhanced, such that MJO‐like modes of variability are rendered either unstable or near neutral, depending on the strength of the shear.
Tulich, S. N.↗
Random access quantum information processors using multimode circuit quantum electrodynamics
Qubit connectivity is an important property of a quantum processor, with an ideal processor having random access—the ability of arbitrary qubit pairs to interact directly. This a challenge with superconducting circuits, as state-of-the-art architectures rely on only nearest-neighbor coupling. Here, we implement a random access superconducting quantum information processor, demonstrating universal operations on a nine-qubit memory, with a Josephson junction transmon circuit serving as the central processor. The quantum memory uses the eigenmodes of a linear array of coupled superconducting resonators. We selectively stimulate vacuum Rabi oscillations between the transmon and individual eigenmodes through parametric flux modulation of the transmon frequency. Utilizing these oscillations, we perform a universal set of quantum gates on 38 arbitrary pairs of modes and prepare multimode entangled states, all using only two control lines. We thus achieve hardware-efficient random access multi-qubit control in an architecture compatible with long-lived microwave cavity-based quantum memories.
97 MATHEMATICS AND COMPUTING↗
RF wave simulation for cold edge plasmas using the MFEM library
A newly developed generic electro-magnetic (EM) simulation tool for modeling RF wave propagation in SOL plasmas is presented. The primary motivation of this development is to extend the domain partitioning approach for incorporating arbitrarily shaped SOL plasmas and antenna to the TORIC core ICRF solver, which was previously demonstrated in the 2D geometry [S. Shiraiwa, et. al., “HISTORIC: extending core ICRF wave simulation to include realistic SOL plasmas”, Nucl. Fusion in press], to larger and more complicated simulations by including a 3D realistic antenna and integrating RF rectified sheath potential model. Such an extension requires a scalable high fidelity 3D edge plasma wave simulation. We used the MFEM [http://mfem.org], open source scalable C++ finite element method library, and developed a Python wrapper for MFEM (PyMFEM), and then a radio frequency (RF) wave physics module in Python. This approach allows for building a physics layer rapidly, while separating the physics implementation being apart from the numerical FEM implementation. An interactive modeling interface was built on pScope [S Shiraiwa, et. al. Fusion Eng. Des. 112, 835] to work with an RF simulation model in a complicated geometry.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Spin transfer torque generated magnetic droplet solitons (invited)
We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90°, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Measuring chirality in NMR in the presence of a time-dependent electric field
Traditional nuclear magnetic resonance (NMR) experiments are “blind” to chirality since the spectra for left and right handed enantiomers are identical in an achiral medium. However, theoretical arguments have suggested that the effective Hamiltonian for spin-1/2 nuclei in the presence of electric and magnetic fields can be different for left and right handed enantiomers, thereby enabling NMR to be used to spectroscopically detect chirality even in an achiral medium. However, most proposals to detect the chiral NMR signature require measuring signals that are equivalent to picomolar concentrations for {sup 1}H nuclei, which are outside current NMR detection limits. In this work, we propose to use an AC electric field that is resonantly modulated at the Larmor frequency, thereby enhancing the effect of the chiral term by four to six orders of magnitude. We predict that a steady-state transverse magnetization, whose direction will be opposite for different enantiomers, will build up during application of an AC electric field. We also propose an experimental setup that uses a solenoid coil with an AC current to generate the necessary periodic electric fields that can be used to generate chiral signals which are equivalent to the signal from a {sup 1}H submicromolar concentration.
36 MATERIALS SCIENCE↗
Phase-only laser control in the weak-field limit: Two-pulse control of IBr photofragmentation revisited
We demonstrate theoretically that laser-induced coherent quantum interference control of asymptotic states of dissociating molecules is possible, starting from a single vibrational eigenstate, after the interaction with two laser pulses—at a fixed time delay—both operating in the weak-field limit. Thus, phase dependence in the interaction with the second fixed-energy phase-modulated pulse persists after the pulse is over. This is illustrated for the nonadiabatic process: I + Br{sup *}←IBr → I + Br, where the relative yield of excited Br{sup *} can be changed by pure phase modulation. Furthermore, a strong frequency dependence of the branching ratio is observed and related to the re-crossing dynamics of the avoided crossing in the above-mentioned process.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Combined fluorescence and phosphorescence lifetime imaging
We present a lifetime imaging technique that simultaneously records the fluorescence and phosphorescence lifetime images in confocal laser scanning systems. It is based on modulating a high-frequency pulsed laser synchronously with the pixel clock of the scanner, and recording the fluorescence and phosphorescence signals by multidimensional time-correlated single photon counting board. We demonstrate our technique on the recording of the fluorescence/phosphorescence lifetime images of human embryonic kidney cells at different environmental conditions.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗