Momentum Coupling Research Articles

Higher‐Order Interactions in Quantum Optomechanics: Revisiting Theoretical Foundations

The theory of quantum optomechanics is reconstructed from first principles by finding a Lagrangian from light’s equation of motion and then proceeding to the Hamiltonian. The nonlinear terms, including the quadratic and higher‐order interactions, do not vanish under any possible choice of canonical parameters, and lead to coupling of momentum and field. The existence of quadratic mechanical parametric interaction is then demonstrated rigorously, which has been so far assumed phenomenologically in previous studies. Corrections to the quadratic terms are particularly significant when the mechanical frequency is of the same order or larger than the electromagnetic frequency. Further discussions on the squeezing as well as relativistic corrections are presented.

Combustion instability mitigation by magnetic fields.

The present interdisciplinary study combines electromagnetics and combustion to unveil an original and basic experiment displaying a spontaneous flame instability that is mitigated as the non-premixed sooting flame experiences a magnetic perturbation. This magnetic instability mitigation is reproduced by direct numerical simulations to be further elucidated by a flow stability analysis. A key role in the stabilization process is attributed to the momentum and thermochemistry coupling that the magnetic force, acting mainly on paramagnetic oxygen, contributes to sustain. The spatial local stability analysis based on the numerical simulations shows that the magnetic field tends to reduce the growth rates of small flame perturbations.

Evaporation Effects in Shock-Driven Multiphase Instabilities

This paper considers the effects of multiphase parameters on a shock-driven particle-laden hydrodynamic instability using simulations performed with the hydrocode FLAG, developed at Los Alamos National Laboratory. The classic sinusoidal interface common in instability literature is created using water particles seeded in a nitrogen–water vapor mixture. The simulations model a shock tube environment as the computational domain, to guide future experimentation. Multiphase physics in FLAG include momentum and energy coupling, with this paper discussing the addition of mass coupling through evaporation. The multiphase effects are compared to a dusty gas approximation, which ignores multiphase components, as well as to a multiphase case which ignores evaporation. Evaporation is then further explored by artificially changing parameters which effect the rate of evaporation as well as the amount of total evaporation. Among all these experiments, the driving force of the hydrodynamic instability is a shock wave with a Mach number of 1.5 and a system Atwood number of 0.11 across the interface. The analysis is continued into late time for select cases to highlight the effects of evaporation during complex accelerations, presented here as a reshock phenomenon. It was found that evaporation increases the circulation over nonevaporating particles postshock. Evaporation was also shown to change the postshock Atwood number. Reshock showed that the multiphase instabilities exhibited additional circulation deposition over the dusty gas approximation. Mixing measures were found to be affected by evaporation, with the most significant effects occurring after reshock.

Effect of noise fluctuation of a quantum tunneling device coupled to a substrate

The recent experiment of Stettenheim, et al. showed that, contrary to conventional belief, the coupling of a quantum electronic device to its substrate can have important effects on the noise power spectrum, since the substrate functions as a mechanical oscillator. We carry out a theoretical analysis of this coupling in the case of a quantum point contact (QPC). First we derive the noise power spectrum from the Hamiltonian without making the Markovian approximation, and obtain numerical results that reproduce the experimental data. Next we investigate the nature of the coupling. In most previous analyses, the coupling of an electronic device to a mechanical oscillator has been modeled as a position coupling. We model it both as a position coupling and as a momentum coupling and compare the results. We find that, as long as one includes backaction between position and momentum, the assumed mode of coupling makes little difference, since the backaction transmits momentum fluctuations to position fluctuations and vice versa. Finally, we ask whether the salient features of the model persist in the Markovian approximation. We find that a Markovian analysis confirms the QPC-substrate coupling, but underestimates the noise floor and leads to excessively sharp and narrow noise peaks around the resonant frequencies.

Mixing of spin and orbital angular momenta via second-harmonic generation in plasmonic and dielectric chiral nanostructures

We present a theoretical study of the characteristics of the nonlinear spin-orbital angular momentum coupling induced by second-harmonic generation in plasmonic and dielectric nanostructures made of centrosymmetric materials. In particular, the connection between the phase singularities and polarization helicities in the longitudinal components of the fundamental and second-harmonic optical fields and the scatterer symmetry properties are discussed. By in-depth comparison between the interaction of structured optical beams with plasmonic and dielectric nanostructures, we have found that all-dielectric and plasmonic nanostructures that exhibit magnetic and electric resonances have comparable second-harmonic conversion efficiency. In addition, mechanisms for second-harmonic enhancement for single and chiral clusters of scatterers are unveiled and the relationships between the content of optical angular momentum of the incident optical beams and the enhancement of nonlinear light scattering is discussed. In particular, we formulate a general angular momenta conservation law for the nonlinear spin-orbital angular momentum interaction, which includes the quasi-angular-momentum of chiral structures with different-order rotational symmetry. As a key conclusion of our study relevant to nanophotonics, we argue that all-dielectric nanostructures provide a more suitable platform to investigate experimentally the nonlinear interaction between spin and orbital angular momenta, as compared to plasmonic ones, chiefly due to their narrower resonance peaks, lower intrinsic losses, and higher sustainable optical power.

Radiation Hydrodynamic Simulations of Dust-driven Winds

Abstract We study dusty winds driven by radiation pressure in the atmosphere of a rapidly star-forming environment. We apply the variable Eddington tensor algorithm to re-examine the two-dimensional radiation hydrodynamic problem of a column of gas that is accelerated by a constant infrared radiation flux. In the absence of gravity, the system is primarily characterized by the initial optical depth of the gas. We perform several runs with different initial optical depths and resolutions. We find that the gas spreads out along the vertical direction, as its mean velocity and velocity dispersion increase. In contrast to previous work using the flux-limited diffusion algorithm, we find little evolution in the trapping factor. The momentum coupling between radiation and gas in the absence of gravity is similar to that with gravity. For Eddington ratio increasing with the height in the system, the momentum transfer from the radiation to the gas is not merely , but amplified by a factor of , where is the integrated infrared optical depth through the system, and , decreasing with the optical depth. We apply our results to the atmosphere of galaxies and conclude that radiation pressure may be an important mechanism for driving winds in the most rapidly star-forming galaxies and starbursts.

Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements.

We discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A2Σ+ - X2Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X2Π(v″ = 0) → A2Σ+(v' = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund's case (a) coupling coefficients aJ and bJ for the X2Π(v″ = 0) rotational level wavefunctions, which are intermediate between Hund's case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients aJ and bJ, although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. In addition, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements.

Quantized phase slips with hysteresis in rotating spin-orbit-coupled Bose-Einstein condensates

Recently, hysteresis has been observed experimentally in a quantized superfluid circuit [S. Eckel, J. G. Lee, F. Jendrzejewski, N. Murray, C. W. Clark, C. J. Lobb, W. D. Phillips, M. Edwards, and G. K. Campbell, Nature (London) 506, 200 (2014)], which is a very important step for developing atomtronic devices. Here we find that quantized phase slips occur as the angular velocity rises, and the average angular momenta are quantized at special angular velocities, immune to the nonlinear interactions. When the spin and orbital angular momentum coupling is introduced, we find that two hysteresis loops could arise for each spin, and there exists a phase slip for spin up in one loop and spin down in the other loop. At the special angular velocities, a phase slip emerges for spin down in the lower state of the loop. Especially, multistability appears if the angular velocity is located in the hysteretic region. These results can promote experimental verification and pave the way for atomtronic devices.

Ablation spot area and impulse characteristics of polymers induced by burst irradiation of 1 µm laser pulses

The ablation spot area and impulse characteristics of various polymers were experimentally investigated against burst irradiation of Nd: YLF laser pulses with a pulse repetition frequency of 1kHz, wavelength of 1047nm, temporal pulse width of 10ns, and single-pulse fluence of 6.1J/cm2 to 17.1J/cm2. The dependences of ablation area on the pulse energy from 0.72 to 7.48mJ and the number of pulses from 10 pulses to 1000 pulses were investigated. In order to characterize their impulse performance as a function of fluence, which should not depend on ablation material, an effective ablation spot area was defined as that obtained against aluminum, 1050A, as the reference material. An impulse that resulted from a single burst of 200 pulses was measured with a torsion-type impulse stand. Various impulse dependences on the fluence, which were not readily predicted from the optical properties of the material without ablation, were obtained. By fitting the experimentally measured impulse performance to Phipps and Sinko's model in the vapor regime, the effective absorption coefficient with laser ablation was evaluated, thereby resulting in three to six orders of magnitude larger than that without ablation. Among the polymers examined using polytetrafluoroethylene (PTFE) as the best volume absorbers, the highest momentum coupling coefficient of 66 μNs/J was obtained with an effective absorption coefficient more than six times smaller than that of the other polymers.

Modulation of spray droplet number density and size distribution by an acoustic field

Multiple interactions may occur when a poly-disperse spray is exposed to an acoustic field. In the context of spray combustion instabilities, acoustic agglomeration, the formation of a droplet number density wave and the modulation of the droplet size distribution are interesting effects. A droplet number density wave, i.e. preferential concentration of droplets in space, may result from size-dependent, one-way momentum coupling between the acoustic field and the spray. The modulation of the droplet size distribution, which has been evidenced in the experimental work of Gurubaran and Sujith (AIAA 2008-1046), is thus a consequence of the droplet number density wave formation. In the present work, the mechanisms that produce these effects are simulated and analyzed in depth by means of computational fluid dynamics. The spray is modeled with both Lagrangian (particles mass-point approach) and Eulerian (continuous phase approach) descriptions. The particular Eulerian method used is a variant of the presumed density function method of moments, which allows to account for the effects of poly-dispersity, in particular the size-dependence of particle velocity. Both the Lagrangian and Eulerian models are validated against experimental data for spray dynamics and spray response to an acoustic field.

The spin Hall effect of light in moving medium

In this paper, we investigate the spin Hall effect of light in moving inhomogeneous medium using the Gordon metric and the Maxwell’s equations in the gravitational field. Light experiences a moving medium as a gravitational field by means of the Gordon metric. It is shown that the spin Hall effect of light is modified by the motion of medium, and the deflection of the ray trajectory is dependent on the polarization and the motion of the medium. It is interesting that there is no coupling of the spin angular momentum of light and the effective gravitational field when the medium is moving along the direction of the gradient [Formula: see text]. The results provide a potential method for controlling the spin Hall effect of light in medium.

Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling

We present a formulation of electromagnetic spin-orbit coupling in magneto-optic media, and propose an alternative source of spin-orbit coupling to non-paraxial optics vortices. Our treatment puts forth a formulation of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media. It shows that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity- and magnetization-dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation. This unidirectional effect produces different orbital angular momenta in opposite directions upon excitation-spin-helicity reversals.

Evaluation of two-group interfacial area transport equation model for vertical small diameter pipes against high-resolution experimental data

Two-phase flow is ubiquitous in industrial, chemical and thermal plants alike. The current state-of-the-art system-code model for predicting fluid transport in two-phase flows is the two-fluid model. In the two-fluid transport model, the coupling of mass, momentum and energy transfer between phases is highly dependent on interfacial area transfer terms. Several research efforts in the past have been focused on the development of an interfacial area transport equation model (IATE) in order to eliminate the drawbacks of static regime flow maps currently used in best-estimate thermal-hydraulic system codes. The IATE attempts to model the dynamic evolution of the vapor/liquid interface by accounting for the different interaction mechanisms affecting gaseous phase transport.The further development and validation of IATE models has been hindered by the lack of adequate experimental data in regions beyond the bubbly flow regime. At the Helmoltz-Zentrum Dresden-Rossendorf (HZDR) experiments utilizing wire-mesh sensors have been performed over all flow regimes, establishing a database of high-resolution (in space and time) data. A 52.3mm diameter pipe with a 16 by 16 wire-mesh sensor operating at 2.5kHz is utilized in the air-water experimental database used in this work. There are a total of 37 tests (with varying superficial gas and liquid velocities, at approximately 0.25MPa). Analysis of IATE performance in the bubbly flow and slug flow regimes is presented.The performance of the Fu-Ishii two-group IATE model is evaluated. In all regions, the interfacial area concentration for small bubbles is predicted well. The model performs poorly in high void fraction regimes, in which large irregularly shaped bubbles are present. The interaction mechanisms that support and deter performance of the IATE model are highlighted. A sensitivity analysis indicates modification of the group-2 wake entrainment coefficient may extend the validity of the Fu-Ishii model. An optimization study is presented to further explore improving IATE performance. It is concluded that the availability of accurate data at high void fractions from the HZDR facility provides a path to improve IATE performance.

Laser ablation impulse generated by irradiating aluminum target with nanosecond laser pulses at normal and oblique incidence

Impulse generation by irradiating aluminum targets with repetitive laser pulses at normal and oblique incidence was investigated using impulse measurements with a torsion pendulum at various incidence angles under different laser beam fluence conditions. The fluence varied from 5.8–20.0 J/cm2 for normal incidence. For oblique incidence, momentum coupling is sensitive to the incident angle at fluences of 6.3 J/cm2 and 9.2 J/cm2 because of target surface reflectivity changes and plume shielding effects. At fluence of 19.3 J/cm2, the fluence on the target surface becomes dominant for impulse generation compared with the angle of incidence effect in a large angular range. Beam fluence optimization for momentum coupling at oblique incidence is discussed based on the impulse characteristics obtained.

Sensitivity analysis of Immersed Boundary Method simulations of fluid flow in dense polydisperse random grain packings

Polydisperse granular materials are ubiquitous in nature and industry. Despite this, knowledge of the momentum coupling between the fluid and solid phases in dense saturated grain packings comes almost exclusively from empirical correlations [2–4, 8] with monosized media. The Immersed Boundary Method (IBM) is a Computational Fluid Dynamics (CFD) modelling technique capable of resolving pore scale fluid flow and fluid-particle interaction forces in polydisperse media at the grain scale. Validation of the IBM in the low Reynolds number, high concentration limit was performed by comparing simulations of flow through ordered arrays of spheres with the boundary integral results of Zick and Homsy [10]. Random grain packings were studied with linearly graded particle size distributions with a range of coefficient of uniformity values (C u = 1.01, 1.50, and 2.00) at a range of concentrations (ϕ ∈ [0.396; 0.681]) in order to investigate the influence of polydispersity on drag and permeability. The sensitivity of the IBM results to the choice of radius retraction parameter [1] was investigated and a comparison was made between the predicted forces and the widely used Ergun correlation [3].

Self-Consistent Field Theory of Ionization Collisions

A self-consistent field (SCF) theory for treating scattering systems was formulated previously and is extended here to the ionization process, in which the continuum orbitals are made square integrable by an amputation procedure. The method is applied to the electron-hydrogen scattering system in the zero angular momentum coupling model, and the differential cross section is compared with the recent results obtained by several other approaches. It is shown that the amputated continuum functions provide an effective projection of the scattering equation. SCF continuum functions generated in the present formalism are used to analyze the effective charge approximation.

General expressions for the matrix elements of the tight-binding operator within the Racah-Wigner algebra*

General expressions for the matrix elements of the tight-binding operator are presented using the Racah-Wigner algebra, where the wave functions are expressed as coupled multiplet wave functions within a given angular momentum coupling scheme. The knowledge of all possible Slater determinants is not necessary and the matrix elements can be written as compact expressions computable with arbitrary accuracy.

Transparency of graphene and other direct-gap two-dimensional materials

Graphene and other two-dimensional materials display remarkable optical properties, including a simple light transparency of $T \approx 1 - \pi \alpha$ for light in the visible region. Most theoretical rationalizations of this "universal" opacity employ a model coupling light to the electron's crystal momentum and put emphasis on the linear dispersion of the graphene bands. However, such a formulation of interband absorption is not allowable within band structure theory, because it conflates the crystal momentum label with the canonical momentum operator. We show that the physical origin of the optical behavior of graphene can be explained within a straightforward picture with the correct use of canonical momentum coupling. Its essence lies in the two-dimensional character of the density of states rather than in the precise dispersion relation, and therefore the discussion is applicable to other systems such as semiconductor membranes. At higher energies the calculation predicts a peak corresponding to a van Hove singularity as well as a specific asymmetry in the absorption spectrum of graphene, in agreement with previous results.

Spin precession: A spin‐1 case study using irreducible tensor operators

AbstractUsing a Cartesian operator basis set, precession equations have previously been derived for spin‐1 systems using some 23 Cartesian operator commutators. We avoid the explicit evaluation of these commutators, and use instead fundamental properties of irreducible tensor operators (ITO) to obtain these precession equations. First, advantage is taken of the angle‐axis parametrization of the rotation matrices that transform second‐rank ITO under rotation to define the unitarily equivalent rotation matrix that transforms second‐rank Cartesian tensors. From this latter transformation, and using simple matrix analysis techniques, all the equations that describe spin‐1 precession in the presence of radiofrequency fields and resonance offsets are obtained. Second, information on the ITO commutation relations can be encoded in angular momentum coupling coefficients in a generalized spin precession equation. In the case of spin‐1, this leads to a set of coupled differential equations for the statistical tensor components . After transformation of these components to their Cartesian counterparts, the corresponding vector differential equations that define the time evolution of the Cartesian operator expectation values are easily solved, again using simple matrix analysis. This solution yields all the equations that describe spin‐1 precession in the presence of radiofrequency fields, resonance offsets, and the quadrupolar interaction.

High energy density soft X-ray momentum coupling to comet analogs for NEO mitigation

We applied MBBAY high fluence pulsed radiation intensity driven momentum transfer analysis to calculate X-ray momentum coupling coefficients CM=(Pas)/(J/m2) for two simplified comet analog materials: i) water ice, and ii) 70% water ice and 30% distributed olivine grains. The momentum coupling coefficients (CM) max of 50×10−5s/m, are about an order of magnitude greater than experimentally determined and computed MBBAY values for meteoritic materials that are analogs for asteroids. From the values for comet analog materials we infer applied energies (via momentum transfer) required to deflect an Earth crossing comet from impacting Earth by a sufficient amount (~1cm/s) to avert collision ~a year in advance. Comet model calculations indicate for CM=5×10−4s/m the deflection of a 2km comet with a density 600kg/m3 by 1cm/s requires an applied energy on the target surface of 5×1013J, the equivalent of 12kT of TNT. Depending on the geometrical configuration of the interaction the explosive yield required could be an order of magnitude higher.