Wave Cavity Research Articles

Gated InAs quantum dots embedded in surface acoustic wave cavities for low-noise optomechanics

Self-assembled InAs quantum dots (QDs) are promising optomechanical elements due to their excellent photonic properties and sensitivity to local strain fields. Microwave-frequency modulation of photons scattered from these efficient quantum emitters has been recently demonstrated using surface acoustic wave (SAW) cavities. However, for optimal performance, a gate structure is required to deterministically control the charge state and reduce the charge noise of the QDs. Here, we integrate gated QDs and SAW cavities using molecular beam epitaxy and nanofabrication. We demonstrate that with careful design of the substrate layer structure, integration of the two systems can be accomplished while retaining the optimal performance of each subsystem. These results mark a critical step toward efficient and low-noise optomechanical systems that truly leverage the excellent properties of semiconductor QDs.

Transmission Loss Characteristics of Dual Cavity Impedance Composite Mufflers for Non-Planar Wave Cavity Resonance

In conventional gasoline automobiles, the engine powers the air conditioning system and engine noise can somewhat mask the noise and vibration of the air conditioning system. In pure electric vehicles, however, the absence of an engine makes the air conditioning system’s noise more noticeable, concentrated in a limited frequency range at constant speeds. As a result, aerodynamic noise from the air conditioning system is a primary noise source in electric vehicles. Pipeline silencers are the main method for reducing this noise. The current silencer design uses plane wave acoustic theory but when cavity modal resonance occurs, the transmission loss error is relatively high. This article addresses the issue of non-planar wave cavity resonance, studying the cavity modal of a muffler using the finite element method to reveal the transmission loss under cavity mode resonance. A dual cavity expansion structure of an impedance composite muffler is proposed, with sound-absorbing materials placed in the cavity to enhance acoustic performance. The analysis of the transmission loss characteristics of the impedance composite muffler provides a theoretical basis for noise control in pure electric vehicle air conditioning systems.

Contrast and Complexity in the Low-Temperature Kinetics of CN(v = 1) with O2 and NO: Simultaneous Kinetics and Ringdown in a Uniform Supersonic Flow.

Bimolecular rate coefficients were determined for the reaction CN(v = 1) + NO and O2 using continuous wave cavity ringdown spectroscopy in a uniform supersonic flow (UF-CRDS). The well-matched time scales for ringdown and reaction under pseudo-first-order conditions allow for the use of the SKaR method (simultaneous kinetics and ringdown) in which the full kinetic trace is obtained on each ringdown. The reactions offer an interesting contrast in that the CN(v = 1) + NO system is nonreactive and proceeds by complex-mediated vibrational relaxation, while the CN(v = 1) + O2 reaction is primarily reactive. The measured rate coefficients at 70 K are (2.49 ± 0.08) × 10-11 and (10.49 ± 0.22) × 10-11 cm3 molecule-1 s-1 for the reaction with O2 and NO, respectively. The rate for reaction with O2 is a factor 2 lower than previously reported for v = 0 in the same temperature range, a surprising result, while that for NO is consistent with extrapolation of previous high-temperature measurements to 70 K. The latter is also discussed in light of theoretical calculations and measurements of the rate constants for the association reaction in the high-pressure limit. The measurements are complicated by the presence of a metastable population of high-J CN formed by photolysis of the precursor BrCN, and a kinetic model is developed to treat the competing relaxation and reaction. It is particularly problematic for reactions at low temperatures where the rotational relaxation and reaction have similar rates, precluding a reliable determination of the rate coefficients at 30 K. Also presented are important modifications to the data acquisition and control for the instrument that have yielded considerably enhanced stability and throughput.

Coherent optical coupling to surface acoustic wave devices

Surface acoustic waves (SAW) and associated devices are ideal for sensing, metrology, and hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to Gaussian surface acoustic wave cavities with small mode volumes and high quality factors (>105 measured here) through a Brillouin-like optomechanical interaction. High-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates are efficiently optically accessed along piezo-active directions, as well as non-piezo-active (electromechanically inaccessible) directions. The precise optical technique uniquely enables controlled analysis of dissipation mechanisms as well as detailed transverse spatial mode spectroscopy. These advantages combined with simple fabrication, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems.

Magnon-Phonon Coupling of Synthetic Antiferromagnets in a Surface Acoustic Wave Cavity Resonator.

We used a surface acoustic wave (SAW) cavity resonator to study the coupling of acoustic magnons in a synthetic antiferromagnet (SAF) and phonons carried by SAWs. The SAF is composed of a CoFeB/Ru/CoFeB trilayer, and the scattering matrix of the SAW resonator is studied to assess the coupling. We find that the spectral line width of the SAW resonator is modulated when the frequency of the excited magnons approaches the SAW resonance frequency. Such a change in the spectral linewidth can be well reproduced using macrospin-like model calculations. From the model analyses, we estimate the magnon-phonon coupling strength to be ∼9.9 MHz at a SAW resonance frequency of 1.8 GHz: the corresponding magnomechanical cooperativity is ∼0.66. As the spectral shape hardly changes in a CoFeB single-layer reference sample, these results show that SAF provides an ideal platform to study magnon-phonon coupling in an SAW cavity resonator.

Inertial Waves in a Nonlinear Simulation of the Sun's Convection Zone and Radiative Interior

Recent observations of Rossby waves and other more exotic forms of inertial oscillations in the Sun’s convection zone have kindled the hope that such waves might be used as a seismic probe of the Sun's interior. Here, we present a 3D numerical simulation in spherical geometry that models the Sun’s convection zone and upper radiative interior. This model features a wide variety of inertial oscillations, including both sectoral and tesseral equatorial Rossby waves, retrograde mixed inertial modes, prograde thermal Rossby waves, the recently observed high-frequency retrograde (HFR) vorticity modes, and what may be latitudinal overtones of these HFR modes. With this model, we demonstrate that sectoral and tesseral Rossby waves are ubiquitous within the radiative interior as well as within the convection zone. We suggest that there are two different Rossby-wave families in this simulation that live in different wave cavities: one in the radiative interior and one in the convection zone. Finally, we suggest that many of the retrograde inertial waves that appear in the convection zone, including the HFR modes, are in fact all related, being latitudinal overtones that are mixed modes with the prograde thermal Rossby waves.

New techniques method for improving the performance of the ALPI Linac

The superconductive quarter wave cavities hadron linac ALPI is the final acceleration stage at the Legnaro National Laboratories. It can accelerate heavy ions from carbon to uranium up to 10 MeV/u for nuclear and applied physics experiments. It is also planned to use it for re-acceleration of the radioactive ion beams for the SPES (Selective Production of Exotic Species) project. In this article, we will present the innovative results obtained with swarm intelligence algorithms, in simulations and measurements. In particular, the increment of the longitudinal acceptance for RIB (Radioactive Ion Beams) acceleration, and beam orbit correction without the beam first-order measurements will be discussed.

The spatial density distribution of H2O2 in the effluent of the COST-Jet and the kINPen-sci operated with a humidified helium feed gas

Abstract Cold atmospheric plasma jets operated with a helium feed gas containing small admixtures of water vapour are excellent sources of H2O2 for direct biomedical applications. However, H2O2 is typically distributed non-uniformly throughout the effluent region, meaning the dosage received by a patient or substrate is dependent on their positioning relative to the plasma source. This study presents the spatial distribution of absolute H2O2 number densities in the effluent of two popular plasma jets, the COST-Jet and the kINPen-sci plasma jet, when operated with a humidified helium feed gas. The measurements were performed using continuous wave cavity ring-down spectroscopy with a tunable, mid-infrared laser. The H2O2 number density measured close to the jet nozzle is 2.3 × 1014 cm−3 for the kINPen-sci plasma jet and 1.4 × 1014 cm−3 for the COST-Jet. The average number density of H2O2 in the effluent of the kINPen-sci plasma jet is a factor of two higher than in the effluent of the COST-Jet. The distribution of H2O2 in the COST-Jet effluent is initially highly uniform and suggests negligible mixing of H2O2 with the ambient air up to 15 mm from the jet nozzle, although it is rapidly diluted at further distances. In the case of the kINPen-sci plasma jet, the number density of H2O2 has a more pronounced radial distribution close to the nozzle, while the mixing with the ambient air is more gradual at further distances from the nozzle. It is evident that a detailed understanding of the H2O2 production in the plasma source, as well as of the transport of H2O2 to the substrate through the effluent, is required in order to optimise the intended effects. This work serves to highlight the difference of the distinct spatial distribution of H2O2 in the effluent of both types of plasma jets when considering their direct application in biomedicine.

Continuous wave cavity ringdown spectroscopy incorporating with an off-axis arrangement, white noise perturbation, and optical re-injection

We present an ultra-sensitive continuous wave cavity ringdown spectroscopy (cw-CRDS) spectrometer to record high resolution spectra of reactive radicals and ions in a pulsed supersonic plasma. The spectrometer employs a home-made external cavity diode laser as the tunable light source, with its wavelength modulated by radio-frequency white noise. The ringdown cavity with a finesse of ∼105 is arranged with an off-axis alignment. The combination of the off-axis cavity and the white-noise perturbed laser yields quasi-continuum laser-cavity coupling without the need of mode matching. The cavity is further incorporated with an extra multi-pass cavity for optical re-injection of light reflected off the master cavity, which significantly increases the throughput power of the high-finesse cavity. A fast switchable semiconductor optical amplifier is used to modulate the cw laser beam to square wave pulses and to initialize timing controlled ringdown events, which are synchronized to the plasma pulses with an accuracy of ∼3 µs. The performance and potential of the cw-CRDS spectrometer are illustrated and discussed, based on the high resolution near-infrared spectroscopic detection of trace 13C13C radicals generated in a pulsed supersonic C2H2/Ar plasma with a pulse duration of ∼50 µs.

Equidistant optimization of elliptical superconducting rf standing wave cavities

Equidistant optimization of elliptical superconducting rf standing wave cavities

A Mid-Infrared Quantum Cascade Laser Ultra-Sensitive Trace Formaldehyde Detection System Based on Improved Dual-Incidence Multipass Gas Cell

Formaldehyde (HCHO) is a tracer of volatile organic compounds (VOCs), and its concentration has gradually decreased with the reduction in VOC emissions in recent years, which puts forward higher requirements for the detection of trace HCHO. Therefore, a quantum cascade laser (QCL) with a central excitation wavelength of 5.68 μm was applied to detect the trace HCHO under an effective absorption optical pathlength of 67 m. An improved, dual-incidence multi-pass cell, with a simple structure and easy adjustment, was designed to further improve the absorption optical pathlength of the gas. The instrument detection sensitivity of 28 pptv (1σ) was achieved within a 40 s response time. The experimental results show that the developed HCHO detection system is almost unaffected by the cross interference of common atmospheric gases and the change of ambient humidity. Additionally, the instrument was successfully deployed in a field campaign, and it delivered results that correlated well with those of a commercial instrument based on continuous wave cavity ring-down spectroscopy (R2 = 0.967), which indicates that the instrument has a good ability to monitor ambient trace HCHO in unattended continuous operation for long periods of time.

Understanding the high-resolution spectral signature of the N2-H2O van der Waals complex in the 2OH stretch region.

We present the observation of the N2-H2O van der Waals complex in the 2OH stretch overtone region. The high-resolution jet cooled spectra were measured using a sensitive continuous wave cavity ringdown spectrometer. Several bands were observed and vibrationally assigned in terms of ν1, ν2, and ν3, the vibrational quantum numbers of the isolated H2O molecule, as (ν1'ν2'ν3')←(ν1″ν2″ν3″)=(200)←(000) and (101) ← (000). A combination band involving the excitation of the in-plane bending motion of N2 and the (101) vibration of water is also reported. The spectra were analyzed using a set of four asymmetric top rotors, each associated with a nuclear spin isomer. Several local perturbations of the (101) vibrational state were observed. These perturbations were assigned to the presence of the nearby (200) vibrational state and to the combination of (200) with intermolecular modes.

High output power, single mode, and TEM00 operation of a multiple gain chip VECSEL using a twisted-mode configuration.

A vertical external cavity surface emitting laser (VECSEL) has been developed for a sodium guide star application. Stable single frequency operation with 21 W of output power near 1178 nm with multiple gain elements while lasing in the TEM00 mode has been achieved. Higher output power results in multimode lasing. For the sodium guide star application, the 1178 nm can be frequency doubled to 589 nm. The power scaling approach used involves using multiple gain mirrors in a folded standing wave cavity. This is the first demonstration of a high power single frequency VECSEL using a twisted-mode configuration and multiple gain mirrors located at the cavity folds.

Tidally excited gravity waves in the cores of solar-type stars: resonances and critical-layer formation

ABSTRACT We simulate the propagation and dissipation of tidally induced non-linear gravity waves in the cores of solar-type stars. We perform hydrodynamical simulations of a previously developed Boussinesq model using a spectral-element code to study the stellar core as a wave cavity that is periodically forced at the outer boundary with a given azimuthal wavenumber and an adjustable frequency. For low-amplitude forcing, the system exhibits resonances with standing g modes at particular frequencies, corresponding to a situation in which the tidal torque is highly frequency-dependent. For high-amplitude forcing, the excited waves break promptly near the centre and spin up the core so that subsequent waves are absorbed in an expanding critical layer (CL), as found in previous work, leading to a tidal torque with a smooth frequency-dependence. For intermediate-amplitude forcing, we find that linear damping of the waves gradually spins up the core such that the resonance condition can be altered drastically. The system can evolve towards or away from g-mode resonances, depending on the difference between the forcing frequency and the closest eigenfrequency. Eventually, a CL forms and absorbs the incoming waves, leading to a situation similar to the high-amplitude case in which the waves break promptly. We study the dependence of this process on the forcing amplitude and frequency, as well as on the diffusion coefficients. We emphasize that the small Prandtl number in the centre of solar-like stars facilitates the development of a differentially rotating core owing to the non-linear feedback of waves. Our simulations and analysis reveal that this important mechanism may drastically change the phase of gravity waves and thus the classical picture of resonance locking in solar-type stars needs to be revised.

Onset of Visible Capillary Waves from High-Frequency Acoustic Excitation.

Remarkably, the interface of a fluid droplet will produce visible capillary waves when exposed to acoustic waves. For example, a small (∼1 μL) sessile droplet will oscillate at a low ∼102 Hz frequency when weakly driven by acoustic waves at ∼106 Hz frequency and beyond. We measured such a droplet's interfacial response to 6.6 MHz ultrasound to gain insight into the energy transfer mechanism that spans these vastly different time scales, using high-speed microscopic digital transmission holography, a unique method to capture three-dimensional surface dynamics at nanometer space and microsecond time resolutions. We show that low-frequency capillary waves are driven into existence via a feedback mechanism between the acoustic radiation pressure and the evolving shape of the fluid interface. The acoustic pressure is distributed in the standing wave cavity of the droplet, and as the shape of the fluid interface changes in response to the distributed pressure present on the interface, the standing wave field also changes shape, feeding back to produce changes in the acoustic radiation pressure distribution in the cavity. A physical model explicitly based upon this proposed mechanism is provided, and simulations using it were verified against direct observations of both the microscale droplet interface dynamics from holography and internal pressure distributions using microparticle image velocimetry. The pressure-interface feedback model accurately predicts the vibration amplitude threshold at which capillary waves appear, the subsequent amplitude and frequency of the capillary waves, and the distribution of the standing wave pressure field within the sessile droplet responsible for the capillary waves.

Electro-mechanical tuning of high-Q bulk acoustic phonon modes at cryogenic temperatures

We investigate the electromechanical properties of quartz bulk acoustic wave resonators at extreme cryogenic temperatures. By applying a DC bias voltage, we demonstrate broad frequency tuning of high-Q phonon modes in a quartz bulk acoustic wave cavity at cryogenic temperatures of 4 K and 20 mK. More than 100 line-widths of tuning of the resonance peak without any degradation in loaded quality factor, which are as high as 1.73×109, is seen for high order overtone modes. For all modes and temperatures, the observed coefficient of frequency tuning is ≈ 3.5 mHz/V per overtone number n corresponding to a maximum of 255.5 mHz/V for the n = 73 overtone mode. No degradation in the quality factor is observed for any value of an applied biasing field.

Phase-dependent strategy to mimic quantum phase transitions

This study proposes a hybrid quantum system of an ensemble of collective spins coupled to a surface acoustic wave (SAW) cavity through a sideband design. Assisted by a dichromatic optical drive with a phase-dependent control, this spin ensemble can effectively mimic different types of long-range Lipkin–Meshkov–Glick (LMG) interactions and then undergo quantum phase transitions (QPTs) due to phase-induced spontaneous symmetry breaking (SSB). In addition, this phase-controlled scheme also ensures the dynamical preparation of the spin-squeezed state (SSS), which may be a useful application in quantum measurement. This study is a fresh attempt at quantum manipulation based on acoustic control and also provides a promising route toward useful applications in quantum information processing, especially the adiabatic preparation of multiparticle-entangled ground states via QPTs; i.e., the Greenberger–Horne–Zeilinger (GHZ) or W-type states.

Beam loading compensation of standing wave linac with off-crest acceleration

In E-Driven positron source of ILC, the generated positron is captured by a standing wave cavity. Because the deceleration capture method is employed, the positron is off-crest over the linac. Because the beam-loading is expected to be more than 1A in a multi-bunch format, the compensation is essential to obtain uniform intensity over the pulse. A conventional method for the compensation controlling the timing doesn’t work because RF and Beam induced field are in different phase. In this manuscript, we discuss the compensation with the off-crest acceleration case. A simple phase modulation on the input RF is a solution.

Numerical Studies on Bow Waves in Intense Laser-Plasma Interaction

Laser-driven wakefield acceleration (LWFA) has attracted lots of attention in recent years. However, few writers have been able to make systematic research into the bow waves generated along with the wake waves. Research about the bow waves will help to improve the understanding about the motion of the electrons near the wake waves. In addition, the relativistic energetic electron density peaks have great potential in electron acceleration and reflecting flying mirrors. In this paper, the bow waves generated in laser-plasma interactions as well as the effects of different laser and plasma parameters are investigated. Multidimensional particle-in-cell simulations are made to present the wake waves and bow waves by showing the electron density and momentum distribution as well as the electric field along x and y directions. The evolution of the bow wave structure is investigated by measuring the open angle between the bow wave and the wake wave cavity. The angle as well as the peak electron density and transverse momentum is demonstrated with respect to different laser intensities, spot sizes, plasma densities, and preplasma lengths. The density peak emits high-order harmonics up to 150 orders and can be a new kind of “flying mirror” to generate higher order harmonics. The study on the bow waves is important for further investigation on the electron motion around the wake waves, generation of dense electron beams, generation of high-order harmonics, and other research and applications based on the bow waves.

Rate constant and branching ratio of the reaction of ethyl peroxy radicals with methyl peroxy radicals.

The cross-reaction of ethyl peroxy radicals (C2H5O2) with methyl peroxy radicals (CH3O2) (R1) has been studied using laser photolysis coupled to time resolved detection of the two different peroxy radicals by continuous wave cavity ring down spectroscopy (cw-CRDS) in their AÃ-X̃ electronic transition in the near-infrared region, C2H5O2 at 7602.25 cm-1, and CH3O2 at 7488.13 cm-1. This detection scheme is not completely selective for both radicals, but it is demonstrated that it has great advantages compared to the widely used, but unselective UV absorption spectroscopy. Peroxy radicals were generated from the reaction of Cl-atoms with the appropriate hydrocarbon (CH4 and C2H6) in the presence of O2, whereby Cl-atoms were generated by 351 nm photolysis of Cl2. For different reasons detailed in the manuscript, all experiments were carried out under excess of C2H5O2 over CH3O2. The experimental results were best reproduced by an appropriate chemical model with a rate constant for the cross-reaction of k = (3.8 ± 1.0) × 10-13 cm3 s-1 and a yield for the radical channel, leading to CH3O and C2H5O, of (ϕ1a = 0.40 ± 0.20).