Resonator Length Research Articles

Proposal for carrier-envelope-phase stable single-cycle attosecond pulse generation in the extreme-ultraviolet range.

A robust method for producing half-cycle-few-cycle attosecond pulses in the extreme ultraviolet spectral range is proposed. It is based on coherent undulator radiation of relativistic ultrathin electron layers (nanobunches), which are produced by nanobunching of ultrashort electron bunches by a 10-TW power laser in a modulator undulator. Our numerical calculations predict the generation of nanobunches shorter than 10nm. By using these electron nanobunches the production of carrier-envelope-phase stable attosecond pulses with up to a few tens of nJ energy and down to 10nm wavelength and 35as duration is predicted.

Nanoscale smoothing of plasmonic films and structures using gas cluster ion beam irradiation

We present a novel method of using gas cluster ion beam irradiation (GCIB) to flatten and widen grains in silver films and structures, while simultaneously, reducing the film thickness with nanometer precision. Ultrathin Ag films produced by GCIB have lower absorbance and better adhesion compared to as-deposited films. By applying the technique post-fabrication to plasmonic color filters, waveguides and disks, we show that an enhanced surface plasmon resonance and propagation length can be achieved.

Accessing the Optical Magnetic Near-Field through Babinet’s Principle

Engineering the optical magnetic field with optical antennas or metamaterials extends the ways to control light-matter interaction. The slot antenna, as the electromagnetic dual of the linear rod antenna, provides the simplest form of a magnetic resonator tunable through its length. Using combined far- and near-field spectroscopy and imaging, and theory, we identify magnetic dipole and higher order bright and dark magnetic resonances at mid-infrared frequencies. From resonant length scaling and spatial near-field distribution, we confirm the applicability of Babinetʼs principle over the mid-infrared spectral region. Babinet's principle thus provides access to spatial and spectral magnetic field properties, leading to the targeted design of magnetic optical antennas.

Studies on Performance of Thermoacoustic Prime Mover

Thermoacoustic engines are the devices that convert thermal energy into acoustic energy without moving parts. The main objective of this study is to analyze the performance of a thermoacoustic prime mover measured in terms of onset temperature difference, frequency, and pressure amplitude by varying resonator, stack length, and plate thickness. From the experiments, it is observed that onset temperature difference and pressure amplitude increases with increase in resonator and stack length with minimum plate thickness, whereas the frequency increases with decrease in resonator and stack length with higher plate thickness. The experimental results are compared with simulated results via Design Environment for Low Amplitude Thermoacoustic Energy Conversion software (Los Alamos National Laboratory, Los Alamos, New Mexico, USA).

Numerical analysis of centered-inclined coupling slots in rectangular waveguides

Numerical analysis is presented for the characteristic parameters of centered-inclined coupling slot in rectangular waveguides, taking into account the transverse distribution of the electric field across the slot aperture. Integral equations are formulated based on dyadic Green’s function theories and solved using the method of moments. Trigonometric basis functions are adopted. It is found that the method will converge with up to ten basis functions. The characteristic parameters can be easily obtained for different slot sizes. Resonant length and resonant resistance of the coupling slots are calculated. It is shown that the calculated results have very high accuracy, compared with simulated results obtained from commercial software. Therefore, it can be effectively applied in the synthesis of antenna arrays. Effects of the transverse distribution on calculating resonant parameters of the coupling slot are also analyzed. The results show that if the transverse distribution of the electric field is neglected, the calculated error tends to become larger when the slot gets wider or thinner.

Simulation Study on Oscillating Cavitation Nozzle for Cleaning Based on FLUENT

Abstract: Based on the basic theory of fluid dynamics and Fluent software, numeric simulation of self-excited oscillating cavitation jet nozzle for cleaning was carried out. The flow field characteristics within tubular organ cavitation nozzle is studied. By numerical simulation, the exit velocity, velocity vector distribution, pressure inside the nozzle as well as static pressure distribution were obtained. The simulation results show that there is a maximum speed at cylindric section inside the cavitation nozzle. When water jet getting into the cylindric section of the cavitation nozzle, there is a significant zone with high negative pressure.Also there is a obvious zone with negative pressure at the outlet end. When the pressure is below the saturation vapor pressure of the liquid, cavitation bubbles occured. Therefore the cavitating water jet was generated. The simulation results also show that there is a higher negative pressure inside the nozzle region when the nozzle inlet diameter Ds = 6 mm, the diameter of the cavity D = 3 mm, the diameter of the cylindric section d = 1.8mm, the resonator length L = 6.2 mm, spread angleα= 60 °, the length of the cylindric segment s = 6 mm, Thererfore it is beneficial effect for the cavitation generating.

Reconfigurable Waveguide Filter with Variable Bandwidth and Center Frequency

This paper presents a center frequency and bandwidth reconfiguration mechanism for waveguide microwave bandpass filters. The filters are designed to be used in the output section of a satellite communication system. While the center frequency of a bandpass filter can be tuned by changing the lengths of the filter resonators, the coupling irises as practical realizations of the impedance inverters cannot easily be adapted to a new value. The novel approach chosen in this paper is to replace the impedance inverters by a novel type of coupling structure. This coupling structure allows adjustment of the coupling by changing the length of a transmission line, which is equivalent to changing the resonant frequency of a coupling resonator. Design equations are presented to transform an impedance inverter into the proposed coupling structure. A synthesis procedure for bandwidth reconfigurable filters is proposed. The feasibility of coupling adaptation is proven based on a full-wave model of the coupling structure. The synthesis process is applied to a four-pole Chebyshev sidewall-coupled circular waveguide filter with 54- and 72-MHz bandwidth settings. The filter is built up and measured. The measured results prove that the filter can be tuned to both bandwidths over a center frequency range of 200 MHz with excellent return loss and insertion loss.

Small-Size Stacked Inverted-F Antenna With Two Hybrid Shorting Strips for the LTE/WWAN Tablet Device

The stacked inverted-F antenna with two hybrid shorting strips placed close to the antenna's feeding strip can provide two wide operating bands to cover long-term evolution/wireless wide-area network operation (698-960/1710-2690 MHz) in the tablet device. The antenna's lower and higher bands are, respectively, contributed by the longer and shorter arms of the antenna. The two hybrid shorting strips include an inductive shorting strip (chip-inductor-loaded strip) and a capacitive shorting strip which capacitively couples to the antenna's shorter arm. The longer arm is also coupled through a chip inductor to the feeding strip such that the longer arm has a decreased resonant length for the low-band operation and, on the other hand, has very small effects on the high-band operation, which is mainly contributed by the shorter arm. The feeding strip is also embedded with a chip capacitor such that an internal high-pass matching circuit formed by the inductive shorting strip and the capacitive feeding strip is obtained to greatly widen the antenna's low-band bandwidth, with small effects on the high-band operation. On the other hand, the capacitive shorting strip is added to greatly enhance the bandwidth of the antenna's higher band, with small effects on the low-band operation. Two wide operating bands are hence easily obtained and adjusted. The antenna can also be recessed in a small ground clearance of 10 × 35 mm 2 inside the tablet device such as a tablet computer in this study. Details of the proposed antenna are presented.

DESIGN OF THE FUZZY CONTROL SYSTEM FOR THE WASTE HEAT UTILIZATION PLANTS DRIVEN BY THE THERMOACOUSTIC ENGINE

The paper addresses the synthesis of fuzzy controllers for computerized control system of the waste heat energy (WHE) utilization plants that operate with the thermoacoustic engine (TAE). Based on the analysis of existing systems, the authors present the main tasks of the synthesized control system, describe its structure and main components. Created system is then tested on the experimental thermoacoustic installation. Using the data obtained authors synthesize the mathematical model of thermoacoustic plant and describe the methodology of its control by the adjustments in resonator length of thermoacoustic device. Using the suggested approach authors design a number of conventional discrete and fuzzy controllers and provide the comparative analysis of quality indicators of the designed control systems transient responses.

Electromagnetic analysis of graphene based tunable waveguide resonators

ABSTRACTThe electromagnetic analysis of the proposed graphene based tunable waveguide resonators for submillimeter‐wave applications is presented. Simple design based on the conventional E‐plane resonator is considered. The desired tunability up to 5% is provided by the change of the effective resonator length. Simulation results are presented to validate the argument. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2385–2388, 2014

Dynamic Properties of Self-Assembled Monolayers of Mercapto Oligo(ethylene oxide) Methyl Ether on an Oscillating Solid–Liquid Interface

The dynamic properties of chemisorbed soft matter on a solid–liquid interface oscillating at megahertz were investigated using a quartz crystal microbalance (QCM). As a chemisorbed soft matter, we employed the self-assembled monolayers of mercapto oligo(ethylene oxide) methyl ethers, HS(CH2CH2O)nCH3 (n = 5, 11, 12, 19, 27, 35, and 43), where those molecular weights had unity. The systematic analyses on the basis of the Voight model revealed that the molecular thickness moving with the solid–liquid interface oscillating at megahertz frequencies, the resonant length, is 8.8 nm, where the frequency dependence of the resonant length is not considered. On the other hand, the analyses based on the Debye process revealed that the logarithm of the resonant length linearly decreases with the logarithm of 2πF, where F is the frequency of the QCM, and varies from 17.3 (9 MHz) to 12.4 nm (81 MHz). Those values in the Debye process were within twice that of the Voight model and were approximately consistent with that ...

Analysis of a Dielectric-Covered Waveguide Slot Antenna Using the Spectrum of Two-Dimensional Solutions

This communication presents an effective and accurate method of computing admittance and resonant characteristics of a single longitudinal waveguide slot, radiating into a dielectric layer. The external magnetic field is computed using the spectrum of two dimensional solutions (S2DS) which reduces a three-dimensional (3D) problem to a 2D problem. S2DS method avoids involving double singular integrals while it only deals with single integral with simple point singularity which needs much less computational effort. The spectrum of the 2D solution is then inverse Fourier transformed to the spatial 3D one. The slot field is determined by Galerkin's method of moments (MoM), then the scattering coefficients and thus the resonant length and conductance are extracted. Computed results are in good agreement with other methods' and measurement data.

A tunable infrared plasmonic polarization filter with asymmetrical cross resonator

A tunable infrared plasmonic polarization filter is proposed and investigated in this paper. The filter is based on the sandwich absorption structure which consists of three layers. The top layer is an array of asymmetrical cross resonator. The middle and bottom layers are dielectric spacer and metal film respectively. By absorbing specific wavelength of the incident light perfectly, the reflection spectrum of the structure shows filter performance. The calculated results show that the absorption wavelength is strongly dependent on the length of branch of the asymmetrical cross resonator which is parallel to the light polarization and independent of the length of the vertical one. Therefore, the asymmetrical cross resonator filter structure opens the way for freely tuning the filtering wavelength for a different light polarization. We can fix a resonant wavelength (absorption wavelength) corresponding to one polarization and change the resonant wavelength for the other polarization by adjusting the corresponding branch length of the asymmetrical cross resonator, or change the two resonant wavelengths of both two polarizations at the same time.

Thin film’s magnetostriction investigated by strain modulated ferromagnetic resonance at low temperature

The novel experimental setup for measurements of magnetostriction of thin films in the temperature range starting from 4.2 K up to the room temperature, using the strain modulated ferromagnetic resonance phenomenon, is presented. The sample under investigation is fixed at the anti-node of vibrations of the longitudinal mode sapphire resonator. The resonator is excited by means of a piezoelectric transducer via the mechanical waveguide. The sapphire rod is put into a helium flow cryostat, thus allowing the measurements in the wide temperature range. The temperature gradient along the resonator length is negligible due to the very high thermal conductivity of sapphire. The setup is controlled by specially designed electronic circuit interfaced to a computer. As an illustrative example, the measurements of epitaxial Fe/GaAs(001) films were performed with in-plane magnetic field, in the temperature range between 10 K and the room temperature.

Small-Size LTE/WWAN Tablet Device Antenna With Two Hybrid Feeds

A small-size tablet device antenna formed by a simple folded metal plate excited by a low-band feed (direct feed with matching network) and a high-band feed (gap-coupled feed with matching network) for the LTE/WWAN operation in the 698-960 and 1710-2690 MHz bands is presented. The folded metal plate has a size of 3 × 5 × 30 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and is disposed in a clearance area of 10 × 30 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (300 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) above the top edge of the device ground plane. The matching network in the low-band feed compensates for additional capacitance for the folded metal plate with a resonant length much less than 0.25 wavelength in the lower band (698-960 MHz) and enhances the antenna's impedance matching to achieve a wide lower band. The matching network in the high-band feed also enhances the antenna's impedance matching to achieve a wide higher band (1710-2690 MHz). In addition, the coupling gap in the high-band feed can reject the low-band frequency. Also, the matching network in the low-band (high-band) feed includes a bandpass circuit which can help reject the high-band (low-band) frequency. Good isolation between the two hybrid feeds can, hence, be obtained, which makes the antenna with simple structure and small size have good radiation performances in both lower and higher bands. Details of the proposed antenna are presented.

Phase-locking and pulse generation in multi-frequency brillouin oscillator via four wave mixing.

There is an increasing demand for pulsed all-fibre lasers with gigahertz repetition rates for applications in telecommunications and metrology. The repetition rate of conventional passively mode-locked fibre lasers is fundamentally linked to the laser cavity length and is therefore typically ~10–100 MHz, which is orders of magnitude lower than required. Cascading stimulated Brillouin scattering (SBS) in nonlinear resonators, however, enables the formation of Brillouin frequency combs (BFCs) with GHz line spacing, which is determined by the acoustic properties of the medium and is independent of the resonator length. Phase-locking of such combs therefore holds a promise to achieve gigahertz repetition rate lasers. The interplay of SBS and Kerr-nonlinear four-wave mixing (FWM) in nonlinear resonators has been previously investigated, yet the phase relationship of the waves has not been considered. Here, we present for the first time experimental and numerical results that demonstrate phase-locking of BFCs generated in a nonlinear waveguide cavity. Using real-time measurements we demonstrate stable 40 ps pulse trains with 8 GHz repetition rate based on a chalcogenide fibre cavity, without the aid of any additional phase-locking element. Detailed numerical modelling, which is in agreement with the experimental results, highlight the essential role of FWM in phase-locking of the BFC.

Exciton-Polaritons with Size-Tunable Coupling Strengths in Self-Assembled Organic Microresonators

Self-assembled nano/microcrystals of organic semiconductors with regular faces can serve as optical microresonators, which hold a promise for studying the light confinement and the light-matter interaction. Here, single crystalline microribbons of 1,4-bis(2-(4-(N,N-di(p-tolyl)amino)phenyl)-vinylbenzene (DPAVB) are synthesized with well-controlled sizes by a facile solution-exchange method. We find that individual microribbon can work as Fabry-Pérot (FP) resonator along its width (w), in which strong coupling of optical modes with excitons results in the formation of exciton polaritons (EPs). The dispersion relation of E ∼ kz of EPs is constructed by extracting the energies (E) of FP resonances at integer multiples of π/w in the wavevector (kz) space. By simulating the significantly curved dispersion of EPs with a two coupled harmonic oscillator model, a coupling strength between 0.48 and 1.09 eV are obtained. Two coupling regimes are classified: in regime I, the coupling strength is constant at 0.48 eV for microribbons with the cavity length of w ≥ 2.00 μm; in regime II, the coupling strength increases dramatically from 0.48 to about 1 eV with decreasing the resonator length from w = 2.00 to 0.83 μm. More significantly, our results suggest that the exciton-photon coupling strength could be modulated by varying the size of microribbon cavities, providing an effective method for engineering the light–matter interaction in organic single crystalline microstructures.

Analysis of cavity-length detuning in diffraction-grating narrowed picosecond optical parametric oscillators

We report on the detailed investigation of picosecond synchronously pumped optical parametric oscillators (OPOs) with a Littrow-mounted diffraction grating as the tuning element, operating close to and far from degeneracy. In addition to the expected line-narrowing effect, we observe a fivefold increase of the resonator-length detuning tolerance when compared to conventional mirror-based OPOs. When the OPO resonator length is altered, we also measure reproducible variations of the emitted wavelength associated with lateral beam displacements that were not reported before. We show that all of these effects can be explained by a geometric adaptation of the resonant beam path within the cavity to maintain a constant cavity round-trip time.

Light Amplification in Derivatives of Pyrazoline-Based Systems

Here we report on experimental results characterizing stimulated emission (SE) and random lasing (RL) phenomena in two new pyrazoline derivatives (PRDs) in comparison with earlier studied 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) dye. Both phenomena were observed in thin films of poly(methyl methacrylate) containing selected dyes upon excitation with 6 ns light pulses delivered by a doubled in frequency Nd:YAG laser (λ = 532 nm, f = 10 Hz). We also report on photodegradation process taking place in the samples during observation of SE and RL and estimate average lifetimes in each case. The pumping threshold levels for observation of random lasing emission amounted from about 1.5 mJ/cm2 to nearly 70 μJ/cm2, depending on pyrazoline dye and for stimulated emission from 16 mJ/cm2 to 5 mJ/cm2, respectively. The resonator lengths related to the RL phenomenon were estimated using the power Fourier transformation method.

Theoretical and experimental investigation of onset characteristics of standing-wave thermoacoustic engines based on thermodynamic analysis

A simplified physical model for calculating the onset temperature ratio and the frequency of a standing wave thermoacoustic engine (SWTE) in the time domain is built based on thermodynamic analysis. Coefficients of transient pressure drop and heat transfer are first deduced from linear thermoacoustic theory. By numerical computation, the evolutions of the pressure amplitude and the spectrum characteristics during the onset process are presented. Furthermore, the effects of stack spacing, charge pressure, and resonator length on the onset temperature ratio and the frequency are calculated. Relatively good agreement between the computational and the experimental results has been achieved, which validates the model for calculating the onset characteristics.