Excitation Of Transverse Modes Research Articles

Dynamical spin structure factors of GeCH3 monolayer due to spin-orbit coupling, strain, and external magnetic field

In this study, we introduced the Kane-Mele model in the presence of an external magnetic field and used a tight-binding approach to examine the dynamical spin susceptibility of the GeCH3 monolayer. We employed Green's function technique to determine the dynamical spin susceptibility behavior of the GeCH3 monolayer in the presence of an external magnetic field, strain, spin-orbit coupling (SOC), electron, and hole doping at room temperature. Our results show that the transverse excitation modes tend to move to lower (higher) frequencies with tensile (compressive) biaxial strain.In addition, the frequency position of the sharp peak in the transversedynamical spin susceptibility is not affected by changes in the external magnetic field, electron doping, or SOC. Also, the influences of the wave vector and doping on the frequency dependence of the transversedynamical spin susceptibility are studied in detail. These results offered here exhibit that the GeCH3 monolayer is appropriate for use in detectors.

Stable single transverse mode excitation in 50 µm core fiber using a photonic-lantern-based adaptive control system.

We report on the generation of single transverse mode output in large-mode-area fiber with a core diameter of 50 µm using a 3×1 photonic-lantern-based adaptive spatial mode control system. We have designed and fabricated the photonic lantern composed of a single mode fibers bundle taper region and a multi-segment multimode fiber splicing region. From simulation and experiments, we demonstrate that the quality of the output beam is significantly influenced by the size of the fibers bundle's waist and the segmented splicing scheme of the multimode fiber. Stable single transverse mode output is achieved at 1064 nm with M2 ∼1.4, which will provide a possible technical solution to increase the mode instability threshold in high power large-mode-area fiber systems.

Total Moment Sum Rule for Magnets in the Vicinity of Quantum Critical Point

It is known that the longitudinal and transverse excitation modes can exist in the vicinity of a quantum critical point in the ordered phase of quantum magnetic systems. The total moment sum rule for such systems is derived on the basis of the extended spin-wave theory, where both longitudinal and transverse magnetic excitations are taken into account. The sum rule is resolved into elastic, one-magnon, and two-magnon components. The formulation is applicable to spin systems with the longitudinal mode, such as $S=1$ systems with single-ion anisotropy of easy-plane type and spin dimer systems. The result helps us analyze and understand measured data of inelastic neutron scattering.

Reduction of Internal Loss and Thermal Resistance in Diode Lasers with Coupled Waveguides

The results of studying edge-emitting quantum-well lasers with a layered design having coupled planar waveguides, capable of suppressing the generation of excited transverse modes, are presented. In this case, a low internal loss (0.4 cm–1) is provided, combined with a small depth (~0.9 μm) of the active region, which results in a low thermal resistance of 6.0 (K/W) mm without a submount.

K -matrix formulation of two-particle scattering in a waveguide in the presence of one-dimensional spin-orbit coupling

The creation of artificial gauge fields in neutral ultracold atom systems has opened the possibility to study the effects of spin-orbit coupling terms in clean environments. This work considers the multi-channel scattering properties of two atoms confined by a wave guide in the presence of spin-orbit coupling terms within a K-matrix scattering framework. The tunability of resonances, induced by the interplay of the external wave guide geometry, the interactions, and the spin-orbit coupling terms, is demonstrated. Our results for the K-matrix elements as well as partial and total reflection coefficients for two identical fermions interacting through a finite-range interaction potential in the singlet channel only are compared with those obtained for a strictly one-dimensional effective low- energy Hamiltonian, which uses the effective coupling constant derived in Zhang et al. [Scientific Reports 4, 1 (2014)] and Zhang et al. [Phys. Rev. A 88, 053605 (2013)] as input. In the regime where the effective Hamiltonian is applicable, good agreement is obtained, provided the energy- dependence of the coupling constant is accounted for. Our approach naturally describes the energy regime in which the bands associated with excited transverse modes lie below a subset of the bands associated with the lowest transverse modes. The threshold behavior is discussed and scattering observables are linked to bound state properties.

Снижение внутренних потерь и теплового сопротивления в лазерных диодах со связанными волноводами

AbstractThe results of studying edge-emitting quantum-well lasers with a layered design having coupled planar waveguides, capable of suppressing the generation of excited transverse modes, are presented. In this case, a low internal loss (0.4 cm^–1) is provided, combined with a small depth (~0.9 μm) of the active region, which results in a low thermal resistance of 6.0 (K/W) mm without a submount.

Structure and dynamics of liquid Zn: an analysis of ab-initio simulations

The static and dynamic properties of liquid Zn have been studied using an ab initio molecular dynamics method. Results are reported for the thermodynamic states at 723K near which inelastic neutron and x-ray scattering data are available. The calculated static structure shows very good agreement with experimental measurements, including an asymmetric main peak. The dynamic structure reveals the existence of propagating density fluctuations, and the associated dispersion relation has also been calculated. The possible coupling between longitudinal and transverse excitation modes has been investigated by looking at specific signatures in two wavevector regions: the first one is located around the position of the main peak of the structure factor, qp , as suggested by the recently reported appearance of high frequency transverse waves in several liquid metals under high pressures; the second region is around qp /2, as suggested by inelastic scattering experiments for liquid Zn and other metals.

Design Considerations for Single-Mode Vertical-Cavity Surface-Emitting Lasers With Impurity-Induced Intermixing

We report on the modeling of 850-nm (Al,Ga)As/GaAs vertical cavity surface-emitting lasers (VCSELs), where the electrical and optical confinement is realized by impurity-induced intermixing. The 3-D simulations of electromagnetic fields are performed by the finite-element method using full vector Maxwell’s equations. An example of a transverse junction VCSEL with Zn-induced intermixing of the areas surrounding the quantum well region is compared with the case of a VCSEL, where the optical modes are confined by selective oxidation of the Al-rich GaAlAs aperture layers. We show that Zn-induced intermixing results in a high efficiency of the leakage of the VCSEL aperture-confined modes into the surrounding intermixed area. Furthermore, there is a strong mode selectivity through the leakage loss between the fundamental and excited transverse modes of the optical cavity. This enables potential realization of a single transverse mode VCSEL at the aperture diameters of 10 $\mu \text{m}$ or above and consequently the realization of high-power single-mode VCSELs. Optimum mode selectivity is realized once the impurity intermixing profile proceeds down to the depth of about 2.6 $\mu \text{m}$ into the bottom distributed Bragg reflector below the quantum well region. Leakage of the optical modes into the intermixed area is accompanied by the evolution of narrow tilted lobes in the far-field emission spectra (at $\sim 60^{\circ }$ tilt angles for the design considered). This effect is similar to the one previously observed in oxide-confined leaky VCSELs and originates from the laterally propagating optical modes outside the non-intermixed aperture region. Where necessary, by applying such phenomenon, a phase-coupled array can be configured. We believe that such single-mode VCSELs may become extremely important in 3-D sensing, printing, and laser illumination. Furthermore, LIDARs with an option of beam steering without moving parts can be realized in 2-D phase-coupled arrays.

Pressure-induced changes in structural and dynamic properties of liquid Fe close to the melting line. An ab initio study

The static and dynamic properties of liquid Fe at high pressure and temperature have been studied using an ab initio molecular dynamics method. We have focused on four thermodynamic states at pressures of 27, 42, 50 and 58 GPa for which x-ray scattering data are available. The calculated static structure shows very good agreement with the available experimental data, including an asymmetric second peak which becomes more marked with increasing pressure. The dynamical structure reveals the existence of propagating density fluctuations and the associated dispersion relation has also been determined. The relaxation mechanisms for the density fluctuations have been analyzed in terms of a model with two decay channels (fast and slow, respectively). We found that the thermal relaxation proceeds along the slow decaying channel whereas the fast one is that of the viscoelastic relaxation. The possible coupling between longitudinal and transverse excitation modes has been investigated by looking at specific signatures in two wavevector regions: the first one is located around the position of the main peak of the structure factor, qp, as suggested by the recently reported appearance of high frequency transverse waves in liquid Li under high pressures; the second region is around qp/2, as suggested by the recent finding of transverse acoustic modes in inelastic x-ray scattering intensities of liquid Fe at ambient pressure. Finally, results are also reported for several transport coefficients.

Effective many-body parameters for atoms in nonseparable Gaussian optical potentials

We analyze the properties of particles trapped in three-dimensional potentials formed from superimposed Gaussian beams, fully taking into account effects of potential anharmonicity and non-separability. Although these effects are negligible in more conventional optical lattice experiments, they are essential for emerging ultracold atom developments. We focus in particular on two potentials utilized in current ultracold atom experiments: arrays of tightly focused optical tweezers and a one-dimensional optical lattice with transverse Gaussian confinement and highly excited transverse modes. Our main numerical tools are discrete variable representations (DVRs), which combine many favorable features of spectral and grid-based methods, such as the computational advantage of exponential convergence and the convenience of an analytical representation of Hamiltonian matrix elements. Optimizations, such as symmetry adaptations and variational methods built on top of DVR methods, are presented and their convergence properties discussed. We also present a quantitative analysis of the degree of non-separability of eigenstates, borrowing ideas from the theory of matrix product states (MPSs), leading to both conceptual and computational gains. Beyond developing numerical methodologies, we present results for construction of optimally localized Wannier functions and tunneling and interaction matrix elements in optical lattices and tweezers relevant for constructing effective models for many-body physics.

Investigation of the Validity of the Universal Scaling Law on Linear Chains of Silver Nanoparticles

Due to the wide range of variation in the plasmonic characteristics of the metallic nanoparticles arranged in linear arrays, the optical spectra of these arrays provide a powerful platform for spectroscopic studies and biosensing applications. Due to the coupling effect between the interacting nanoparticles, the excited resonance mode is shifted with the interparticle separation. The change in the resonance energy of the coupled mode is expressed by the fractional plasmon shift which would normally follow a universal scaling behavior. Such a universal law has been successfully applied on a system of dimers under parallel polarization. It has been found that the plasmon shift decays exponentially over interparticle spacing. The decay length is independent of both the nanoparticle and dielectric properties of the surrounding medium. In this paper, the discrete dipole approximation (DDA) is used to examine the validity of extending the universal scaling law to linear chains of several interacting nanoparticles embedded in various host media for both parallel and perpendicular polarizations. Our calculations reveal that the decay length of both the coupled longitudinal mode (LM) and transverse modes (TM) is strongly dependent on the refractive index of the surrounding medium (nm). The decay constant of the LM is linearly proportional to nm while the corresponding constant of the TM decays exponentially with nm. Upon changing the nanoparticle size, the change in the peak position of the LM decreases exponentially with the interparticle separation and hence, it obeys the universal law. The sensitivity of coupled LM to the nanoparticle size is more pronounced at both smaller nanoparticle sizes and separations. The sensitivity of the coupled TM to the nanoparticle size on the other hand changes linearly with the separation and therefore, the universal law does not apply in the case of the excited TM.

Nonlinear frequency-dependent effects in the dc magnetization of uniaxial magnetic nanoparticles in superimposed strong alternating current and direct current fields

The dc component of the magnetization of noninteracting fine magnetic particles possessing simple uniaxial anisotropy and subjected to strong ac and dc bias magnetic fields is calculated via the magnetic Langevin equation. In the presence of an ac driving field, the dc component of the magnetization of uniaxial particles alters drastically leading to new nonlinear effects; in particular, it becomes frequency-dependent. In axial symmetry, where the strong ac field is parallel to the easy axis of a particle, two distinct dispersion regions in the dc magnetization at low and mid-frequencies emerge, corresponding to longitudinal overbarrier and intrawell relaxation modes. Such frequency-dependent behavior allows one to estimate the magnetization reversal time via the half-width of the low-frequency dispersion band. Otherwise, by applying the strong ac field at an angle to the easy axis of a particle so breaking the axial symmetry, a third high-frequency nonlinear resonant dispersion in the dc component of the magnetization appears accompanied by parametric resonance behavior due to excitation of transverse modes with frequencies close to the precession frequency.

Quantitative study of quasi-one-dimensional Bose gas experiments via the stochastic Gross-Pitaevskii equation

The stochastic Gross-Pitaevskii equation is shown to be an excellent model for quasi-one-dimensional Bose gas experiments, accurately reproducing the in situ density profiles recently obtained in the experiments of Trebbia et al. [Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett. 100, 090402 (2008)], and the density fluctuation data reported by Armijo et al. [Phys. Rev. Lett. 105, 230402 (2010)]. To facilitate such agreement, we propose and implement a quasi-one-dimensional stochastic equation for the low-energy, axial modes, while atoms in excited transverse modes are treated as independent ideal Bose gases.

Observation of the first excited transverse mode in guided matter waves

In direct analogy to the textbook example of light guided in a few-mode fiber (FMF), we report the observation of the first excited mode of an optically guided atomic beam. We selectively excite the atomic analog of the LP₀₁ optical mode by controlling the energy distribution of ultracold atoms loaded into the guide, resulting in a modal structure dominated by a 47(2)% population in the first excited transverse mode. The ability to guide lower-order modes has been essential to demonstrating optical effects such as multimode interferometry, slow light, and entanglement, and an atomic analog to a FMF may lead to similarly useful applications.

液体金属の横波モード：教科書の常識を覆すのか？

液体金属の横波モード：教科書の常識を覆すのか？

Cavity-enhanced absorption spectroscopy with a red LED source for NOx trace analysis

Incoherent broad-band cavity-enhanced absorption spectroscopy (IBB-CEAS) based on arc lamps has been around for a few years, but only two reports exist using light-emitting diodes (LEDs). We present a setup based on a 643-nm LED which is of interest for the simultaneous detection of NO3 and NO2. The latter is chosen for testing as it is stable and available in calibrated diluted samples. A detection limit in the ppbv range is obtained with 2-min averaging (5×10-9 /cm rms baseline noise level), comparable to the best performance of chemiluminescence devices used for pollution monitoring. At 1-s acquisition time, the detection limit is below 10 ppbv. Extrapolation to NO3 yields a detection limit of a few pptv for a few minutes averaging. We also test the retrieval of absolute sample absorption (and concentration) using the cavity mirror reflectivity obtained with a commercial spectrophotometer, and we conclude that a calibration based on a reference sample of known concentration is preferable for accurate concentration measurements with IBB-CEAS. Finally, we present a rigorous frequency-domain derivation of cavity transmission as a function of wavelength for a broad-band spectrally smooth source, which complements the time-domain derivation by Fiedler et al. This derivation exposes an issue with multiple transverse mode excitation inherent to this technique, which may result in slightly distorted spectral profiles.

Efficient generation of the first waveguide mode in the InGaAs/GaAs/InGaP heterolaser

Generation of the first excited transverse mode (TE1) in a new InGaAs/GaAs/InGaP diode heterolaser with a thin InGaP layer at the waveguide center was studied. This laser design decreases the competition of the first and fundamental modes and provides TE1 mode lasing at a threshold current comparable to that of an ordinary laser oscillating at the fundamental TE0 mode.

The possibility of transverse excitation modes in liquid Ga

The dynamic structure factor S(Q,ω) of liquid Ga was measured at 100 °C using a high resolution inelastic x-ray scattering (IXS) spectrometer at 3-ID-C/APS. Thespectra obtained clearly demonstrate the existence of longitudinal propagating modes at smallQ values, like aprevious IXS result at 42 °C obtained by Scopigno et al and an inelastic neutron scattering (INS) one at47 °C obtained by Bove et al, but unlike an INS study at57 °C by Bermejo et al. The dispersion relation of the excitations deviates positively from thehydrodynamic prediction by about 13%. There are two new findings from thisexperiment. Firstly, an additional lower energy excitation is necessary to reproduceS(Q,ω) spectra inthe Q rangebeyond 10 nm−1, in agreement with the result of a first-principles molecular dynamic simulation,which may indicate a transverse acoustic mode in this peculiar liquidmetal. Secondly, the quasielastic line comprises a Gaussian contribution atQ values near thefirst maximum in S(Q), which may indicate the existence of short-lived covalent correlation in liquid Ga with alifetime of 0.39 ps.

Selective modal excitation using phase-shifted ultrasound radiation force

The ultrasound radiation force can be used as a noncontact method for exciting vibrational modes. In one implementation, an audio-range modulation signal is combined with a 40-kHz carrier to form a double-sideband suppressed-carrier (DSSC) waveform that is emitted from an ultrasound transducer. The frequency of the ultrasound radiation force is the difference between the frequencies of the sidebands, therefore at twice the modulation frequency. We describe a method for selective mode excitation using a transducer pair, each emitting a DSSC signal. The modulation signal for one transducer was phase shifted relative to the other transducer. When the two modulation signals were in phase, the radiation stress field was uniform. For devices studied, this excited transverse modes while suppressing torsional modes. Similarly, if the modulation signals were out of phase, torsional modes were excited while suppressing transverse modes. This technique has been demonstrated for devices including an MEMS mirror, hard-drive suspension, and brass cantilever. For a cantilever, the ratio of the amplitudes of 180-Hz transverse over 1.3-kHz torsional modes was varied by over two orders of magnitude by shifting the phase difference between the two beams over a range of 90 deg. This noncontact technique allows control over the types of vibration excited.

Beam–plasma interaction in strongly coupled plasmas

The well-known problem of beam–plasma instability acquires new aspects when one or both of the two components (the beam and the plasma) are strongly interacting. We have now theoretically considered the case when the plasma is in the solid phase and forms a lattice. In this situation, the inherent anisotropy of the lattice leads to a coupling between the longitudinal and transverse polarizations. One of the novel features of the beam–plasma instability in this scenario is the possible excitation of transverse modes, which should be an experimentally observable signature of the instability. We have initially concentrated on a 2D toy model with the beam lying in the lattice plane. At the same time, we have initiated a molecular dynamics simulation program for studying various aspects of the penetration of a beam into a plasma lattice. The beam parameters can be adjusted in order to see the effects of increasing coupling strength within the beam and to distinguish between collective phenomena and scattering on individual particles. When both components are strongly interacting, a number of remarkable phenomena—trapping of beam particles, creation of dislocations, local melting of the lattice—may be observed.