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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Microwave-induced zero-resistance state in two-dimensional electron systems with unidirectional periodic modulation

In this study we fabricated lateral superlattices (LSLs) based on the selectively doped GaAs/AlAs heterostructures with a high-mobility two-dimensional (2D) electron gas. The LSLs were formed using the electron-beam lithography and lift-off techniques, which produced a set of metallic strips on top of a heterojunction. The amplitude of the 2D electron gas modulation in the LSL was controlled by the gate voltage applied to the metallic strips. The LSLs with two different periods (a = 200 nm and 500 nm) were used to investigate the influence of microwave radiation with the frequency of 110–150 GHz on the 2D electron transport at the temperature T = 1.6 K in the magnetic field B < 1 T. We have found that zero-resistance states (ZRSs) appear under the microwave radiation in the 2D systems with a unidirectional periodic modulation. These ZRSs are located at the minima of commensurability oscillations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electric field-induced transport modulation in VO{sub 2} FETs with high-k oxide/organic parylene-C hybrid gate dielectric

We report on the observation of reversible and immediate resistance switching by high-k oxide Ta{sub 2}O{sub 5}/organic parylene-C hybrid dielectric-gated VO{sub 2} thin films. Resistance change ratios at various temperatures in the insulating regime were demonstrated to occur in the vicinity of phase transition temperature. We also found an asymmetric hole-electron carrier modulation related to the suppression of phase transition temperature. The results in this research provide a possibility for clarifying the origin of metal-insulator transition in VO{sub 2} through the electrostatic field-induced transport modulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

High-speed modulator with interleaved junctions in zero-change CMOS photonics

A microring depletion modulator is demonstrated with T-shaped lateral p-n junctions used to realize efficient modulation while maximizing the RC limited bandwidth. The device having a 3 dB bandwidth of 13 GHz has been fabricated in a standard 45 nm microelectronics CMOS process. The cavity has a linewidth of 17 GHz and an average wavelength-shift of 9 pm/V in reverse-bias conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Resonant transducers for solid-state plasma density modulation

We have developed transducers capable of modulating the plasma density and plasma density gradients in indium antimonide. These transducers make use of piezoelectric drivers to excite acoustic pressure resonance at 3λ/2, generating large amplitude standing waves and plasma density modulations. The plasma density has been directly measured using a laser diagnostic. A layered media model shows good agreement with the experimental measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Drift waves enstrophy, zonal flow, and nonlinear evolution of the modulational instability

The interaction of the drift wave (DW) turbulence and zonal flow (ZF) is investigated with the modified Hasegawa–Mima equation taking into account the backreaction of ZF velocity on DW turbulence. It is shown that the y-averaged enstrophy of DW turbulence and the velocity of ZF are intrinsically related. By utilizing this feature, a nonlinear stage of DW modulational instability is considered within the framework of the wave kinetic equation. It is shown that in this approximation, the nonlinear stage of the modulational instability results in the collapsing solutions, accompanied by the “wave breaking” phenomenon. Numerical simulations based on the Hasegawa–Mima equation show that for a weak DW turbulence, Φ ̃ = ( e φ ̃ / T e ) ( L n / ρ s ) ⪝ 1 , the collapsing-like features on both ZF and y-averaged enstrophy of DW turbulence decay in time and then re-emerge again at different locations. For the case of a strong DW turbulence, Φ ̃ > 1 , where nonlinear interactions of DW harmonics dominate, stable spatial structures of ZF and y-averaged enstrophy of DW turbulence emerge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Iodine photodissociation laser with an intracavity space - time light modulator

A scheme of an iodine laser with two different intracavity space - time modulators based on electrooptic PLZT ceramics is experimentally studied. It is shown that lasing can occur in different angular directions with the use of both modulators. The output laser energy is 10 mJ with a pulse duration of 200 {mu}s and a beam divergence of 6.3 Multiplication-Sign 10{sup -4} rad. The laser field of view (5.1 Multiplication-Sign 10{sup -3} rad) consists of a discrete set of 8 Multiplication-Sign 8 directions. (control of laser radiation parameters)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Cascade amplification of self-similar frequency-modulated pulses in normal group velocity dispersion active fibres

This paper examines the possibility of efficient amplification of self-similar frequency-modulated wave packets in longitudinally inhomogeneous active fibres. We analyse the dynamics of parabolic pulses with a constant frequency modulation rate and derive algorithms for optimising the group velocity dispersion profile in order to ensure self-similar propagation of such pulses. We demonstrate that the use of a cascade scheme can ensure efficient amplification of individual subpicosecond pulses of this type. (optical fibres, lasers and amplifiers. properties and applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Self-modulation oscillation regimes in fibre lasers with microoptomechanical resonance structures

Self-modulation oscillation regimes are studied in erbium fibre lasers with intracavity microoptomechanical structures (microoscillators) of different types, namely, based on silicon structures and consisting of special waveguide segments. Optical excitation of acoustomechanical vibrations of microoscillators is accomplished using photothermal effect or light pressure. Under the conditions of resonance interaction, i.e., when the eigenfrequencies of microoscillators coincide with the frequencies of relaxation oscillations or with those of intermode beats, the dependences of self-oscillation characteristics on the system parameters are found and the stability of the self-modulation frequency within 10{sup -4} - 10{sup -6} is obtained at relatively low (40 - 300) Q-factors of microoscillators. The possibility to construct multivariate (multichannel) fibreoptical sensors of physical quantities with frequency division of measurement channels is demonstrated. (optical fibres, lasers and amplifiers. properties and applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Diode amplifier of modulated optical beam power

Analytical relations are obtained between characteristics of modulated light at the output and input of an optical diode power amplifier operating in the highly saturated gain regime. It is shown that a diode amplifier may act as an amplitude-to-phase modulation converter with a rather large bandwidth (∼10 GHz). The low sensitivity of the output power of the amplifier to the input beam power and its high energy efficiency allow it to be used as a building block of a high-power multielement laser system with coherent summation of a large number of optical beams. (lasers)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Frequency modulation of semiconductor disk laser pulses

A numerical model is constructed for a semiconductor disk laser mode-locked by a semiconductor saturable absorber mirror (SESAM), and the effect that the phase modulation caused by gain and absorption saturation in the semiconductor has on pulse generation is examined. The results demonstrate that, in a laser cavity with sufficient second-order dispersion, alternating-sign frequency modulation of pulses can be compensated for. We also examine a model for tuning the dispersion in the cavity of a disk laser using a Gires–Tournois interferometer with limited thirdorder dispersion. (control of radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Frequency modulation and compression of optical pulses in an optical fibre with a travelling refractive-index wave

We have studied the conditions for spectral broadening, frequency modulation and compression (both temporal and spectral) of Gaussian pulses propagating in a fibre with a travelling refractive-index wave. Analytical expressions have been derived for the dependences of pulse duration, chirp and spectral width on the distance travelled through the fibre, parameters of the fibre and radiation launched into it. Based on the numerical analysis we have studied the behaviour of these characteristics by changing the coefficient of the refractive-index modulation and other parameters of the travelling refractive-index wave. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Compensation for nonlinear effects in an optical orthogonal frequency-division multiplexed signal using adaptive modulation

We study the influence of nonlinear effects on symbol error statistics when a 16-QAM orthogonal frequency-division multiplexed signal is transmitted in a 1000 km length of fibre. A technique of adaptive modulation is proposed for generating signals that are resistant to nonlinear distortions. A considerable improvement of the transmission quality is shown to take effect in using an adaptive modulation scheme. (paper)

42 ENGINEERING↗
DOE OSTI2017

Amplitude/phase modulation and spectrum of the vertical-cavity surface-emitting laser output

A new approach has been proposed for analysing the dynamics of the laser field amplitude on the basis of Maxwell’s equations. This approach has been used to develop a theory for calculating modulation characteristics of vertical-cavity surface-emitting lasers in the small modulation limit. The present analysis allows one to sequentially examine the dynamics of the amplitude and phase of the electromagnetic field of light in the framework of a single physical model, proceeding from fundamental principles. The proposed approach offers a natural and unique procedure for finding all laser cavity parameters necessary for calculation. An analytical calculation in the ‘small’-signal approximation has ensured good agreement with experimental data. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Laser autodyne registration of nanodisplacements under laser wavelength modulation

The formation of an autodyne interference signal under the current modulation of the laser radiation wavelength is studied. For the first time we propose a method for determining the stationary phase of the autodyne signal based on the analysis of the low-frequency spectrum of the laser autodyne system. The results of measuring nanodisplacements of the electromagnetic translator by the ratio of the autodyne signal spectral components under harmonic current modulation of the laser autodyne wavelength are presented. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

QML-generation dynamics of a solid-state laser with an acousto-optic travelling wave modulator

The features of the generation dynamics of a laser with an acousto-optic modulator are studied. The light field injection with a frequency shift from the previous mode to the subsequent one ensures mode locking, and in many cases contributes to the instability and self-oscillations at the laser relaxation frequency. The amplitude and frequency characteristics of the emerging regime, along with the features of the regimes realised under external modulation of the diffraction coupling coefficient, are analysed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Self-modulation oscillations in a solid-state coupled-cavity ring laser

We propose a theoretical model describing the radiation dynamics in a solid-state coupled-cavity ring laser. Based on the numerical simulation conducted within the framework of this model, we investigate antiphase harmonic oscillations of counterpropagating wave intensities. It is shown that the amplitudes and frequencies of self-modulation oscillations in cases of in-phase and antiphase cavity couplings differ significantly. In the case of antiphase coupling, a new possibility of increasing the scale factor with increasing perimeter of the additional cavity is found. The dependence of the frequency of self-modulation oscillations on the optical nonreciprocity produced in the main cavity by a constant magnetic field is studied experimentally. Comparison of experimental and theoretical results shows good agreement between theory and experiment. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Laser cooling of {sup 171}Yb{sup +} ions in a frequency-modulated field

We have investigated the laser cooling of ytterbium ions in a radio-frequency trap by a frequency-modulated resonant laser field. It has been shown that the lowest laser cooling temperatures, close to the Doppler limit, can be reached at field modulation parameters μ ⩾ 0.1. At lower μ values, the region of field parameters optimal for cooling shifts to higher intensities and the minimum possible laser cooling temperature increases. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

New modulation method in acousto-optic spectrometers

A new method is proposed for modulating radiation in collinear acousto-optic (AO) spectrometers, which is based on the sequential diffraction of incident polarised optical radiation using two sound packets with the same frequencies and initial phases. A theory of diffraction of optical radiation on two successive packets of sound waves propagating in a crystal is constructed, and the instrumental function of the AO spectrometer is found. It is established that the instrumental function of such a spectrometer becomes time-dependent, and the modulation frequency of this dependence, in turn, depends on the intensity of the sound wave and on the detuning from the phase-matching conditions. The frequency dependence of the measured photocurrent for some finite number of sound packets is obtained explicitly, and it is shown that its measurement allows the spectral composition of the incident optical radiation to be determined with greater accuracy. (invited paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

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