Resonance Frequency Of Cavity Research Articles

Waveguide detuning caused by transverse magnetic fields on a simulated in‐line 6 MV linac

Due to the close proximity of the linear accelerator (linac) to the magnetic resonance (MR) imager in linac-MR systems, it will be subjected to magnet fringe fields larger than the Earth's magnetic field of 5 x 10(-5) T. Even with passive or active shielding designed to reduce these fields, some magnitude of the magnetic field is still expected to intersect the linac, causing electron deflection and beam loss. This beam loss, resulting from magnetic fields that cannot be eliminated with shielding, can cause a detuning of the waveguide due to excessive heating. The detuning, if significant, could lead to an even further decrease in output above what would be expected strictly from electron deflections caused by an external magnetic field. Thus an investigation of detuning was performed through various simulations. According to the Lorentz force, the electrons will be deflected away from their straight course to the target, depositing energy as they impact the linac copper waveguide. The deposited energy would lead to a heating and deformation of the copper structure resulting in resonant frequency changes. PARMELA was used to determine the mean energy and fraction of total beam lost in each linac cavity. The energy deposited into the copper waveguide from the beam losses caused by transverse magnetic fields was calculated using the Monte Carlo program DOSRZnrc. From the total energy deposited, the rise in temperature and ultimately the deformation of the structure was estimated. The deformed structure was modeled using the finite element method program COMSOL MULTIPHYSICS to determine the change in cavity resonant frequency. The largest changes in resonant frequency were found in the first two accelerating cavities for each field strength investigated. This was caused by a high electron fluence impacting the waveguide inner structures coupled with their low kinetic energies. At each field strength investigated, the total change in accelerator frequency was less than a manufacturing tolerance of 10 kHz and is thus not expected to have a noticeable effect on accelerator performance. The amount of beam loss caused by magnetic fringe fields for a linac in a linac-MR system depends on the effectiveness of its magnetic shielding. Despite the best efforts to shield the linac from the magnetic fringe fields, some persistent magnetic field is expected which would result in electron beam loss. This investigation showed that the detuning of the waveguide caused by additional electron beam loss in persistent magnetic fields is not a concern.

Time-domain measurement of optical transport in silicon micro-ring resonators

We perform time-domain measurements of optical transport dynamics in silicon nano-photonic devices. Using pulsed optical excitation the thermal and carrier induced optical nonlinearities of micro-ring resonators are investigated, allowing for identification of their individual contributions. Under pulsed excitation build-up of free carriers and heat in the waveguides leads to a beating oscillation of the cavity resonance frequency. When employing a burst of pulse trains shorter than the carrier life-time, the slower heating effect can be separated from the faster carrier effect. Our scheme provides a convenient way to thermally stabilize optical resonators for high-power time-domain applications and nonlinear optical conversion.

Observability of radiation-pressure shot noise in optomechanical systems

We present a theoretical study of an experiment designed to detect radiation pressure shot noise in an optomechanical system. Our model consists of a coherently driven optical cavity mode that is coupled to a mechanical oscillator. We examine the cross-correlation between two quadratures of the output field from the cavity. We determine under which circumstances radiation pressure shot noise can be detected by a measurement of this cross-correlation. This is done in the general case of nonzero detuning between the frequency of the drive and the cavity resonance frequency. We study the qualitative features of the different contributions to the cross-correlator and provide quantitative figures of merit for the relative importance of the radiation pressure shot noise contribution to other contributions. We also propose a modified setup of this experiment relevant to the "membrane-in-the-middle" geometry, which potentially can avoid the problems of static bistability and classical noise in the drive.

TH‐D‐BRB‐08: The Effect of Transverse Magnetic Fields on a Simulated In‐Line 6 MV Linac

Purpose: The linac waveguide is subjected to large magnetic fringe fields in a linac‐MR hybrid system. An investigation is performed to determine the effect of transverse magnetic fields on a simulated in‐line 6 MV medical linac. Method and Materials: The program PARMELA was used calculate the electron beam loss per cavity with the linac waveguide subjected to external transverse fields. BEAMnrc and DOSXYZnrc were used to calculate the effect on 40×40 and 20×20 cm2 field dose profiles and depth dose curves with the linac submersed in a transverse magnetic field. DOSRZnrc was used to determine the heating per cavity as a result of the beam loss and COMSOL was used to determine the resulting cavity resonant frequency changes due to cavity heating. Lastly a calculation of leakage radiation caused by the excessive beam loss was performed using BEAMnrc. Results: The beam loss was calculated to be 5±1 22±1 and 49±1% over nominal for 2 4 and 6 G magnetic fields respectively. The transverse magnetic fields caused a shifting of the electron spatial distribution at the target which resulted in a lateral shift of the dose profiles making 14.4% of all points fail a 1%/1mm acceptance criterion at a 6 G field. Through asymmetric jaw positions the lateral shift in the dose profiles was reduced such that only 0.5% of all points failed. The frequency of the accelerating mode changed by 0.03 Hz due to heating and a total leakage radiation of 0.007% of the radiation field was calculated. Conclusion: The 6 MV linac investigated showed sufficient tolerance to be used in transverse magnetic fields larger than earth's field. The shifts observed in the dose profiles were reduced through asymmetric jaw positions such that only 0.5 % of the points failed a 1 %/ 1 mm criterion at 6 G.

Sensing the soot load in automotive diesel particulate filters by microwave methods

Modern vehicles with diesel engines need to be equipped with particulate filters (DPFs) to meet today's and tomorrow's stringent emission regulations. Such filters must be regenerated on a regular basis to burn off the soot adsorbed in the course of time. As the regeneration processes consume fuel, they must be kept to the bare minimum which requires a detailed knowledge of the actual soot load in the filter. We have investigated if the soot load can be determined in situ by the cavity perturbation method at operating frequencies in the low GHz range. We will show that, indeed, current microwave technology as used, for instance, in cellular phones is capable of detecting the soot load in a diesel particulate filter. Experimentally observed sensitivities of cavity resonance frequencies to soot load (adsorbed mass) were as high as 3 MHz g−1. This contribution reports on the measurement approach, experimental results obtained in industrial dynamometer test benches and the conclusions to be drawn from the results.

Efficient second-harmonic generation using a semiconductor tapered amplifier in a coupled ring-resonator geometry

A new approach for efficient second-harmonic generation using diode lasers is presented. The experimental setup is based on a tapered amplifier operated in a ring resonator that is coupled to a miniaturized enhancement ring resonator containing a periodically poled lithium niobate crystal. Frequency locking of the diode laser emission to the resonance frequency of the enhancement cavity is realized purely optically, resulting in stable, single-frequency operation. Blue light at 488 nm with an output power of 310 mW is generated with an optical-to-optical conversion efficiency of 18%.

RF injection-locking of terahertz quantum cascade lasers

It is demonstrated that the cavity resonance frequency – the round-trip frequency – of terahertz quantum cascade lasers can be injection-locked by direct modulation of the bias current using an RF source. Metal-metal and single-plasmon waveguide devices with round-trip frequencies up to 35 GHz have been studied, and show locking ranges above 200 MHz. A square-root dependence of the locking range with RF-power was found to be in agreement with classical injection-locking theory. Inside this locking range the laser round-trip frequency is phase-locked, with a phase noise determined by the RF-synthesiser, leading to the generation of modelocked pulses with low timing jitter.

Efficient characterization of microwave applicator loaded with multilayer dielectric based on neural networks

In this paper, new neural network approach for characterization of cylindrical metallic cavity loaded with multilayer dielectric is suggested. Such cavity configuration has a great importance in realization of microwave resonant applicators, widely used for thermal processing of multilayer materials. Proposed neural model is based on representation of multilayer cavity load via several planparallel homogeneous dielectric slabs and superposition of separate influence of each dielectric slab parameters on the cavity resonant frequency. Model is incorporated into MLP neural network enabling its efficient implementation on modest hardware platform. Suggested approach is verified on the example of circular cylindrical metallic cavity loaded with two-layer dielectric.

A METHOD TO DESIGN DUAL-BAND, HIGH-DIRECTIVITY EBG RESONATOR ANTENNAS USING SINGLE-RESONANT, SINGLE-LAYER PARTIALLY REFLECTIVE SURFACES

A new method is presented to design dual-band, high- directivity, EBG-resonator antennas using simple, single-resonant, single-layer partially re∞ective surfaces (PRS). The large, positive gradient of the re∞ection phase versus frequency curve of partially re∞ecting surfaces, observed only close to the resonance frequency of the PRS, is exploited for this purpose. An example single-resonant PRS, based on a frequency-selective surface (FSS) composed of a printed slot array, was designed. Then it is used to design an EBG- resonator antenna to demonstrate the feasibility of achieving dual-band performance. Cavity models are employed, together with the re∞ection characteristics of the PRS, to understand the operation of the device at critical frequencies such as cavity resonance frequencies and the PRS resonance frequency. Antenna simulations and computed results conflrm the dual-band operation of this very simple, single-layer, low- proflle EBG-resonator antenna. It resonates in two bands centered at 10.5GHz and 12.3GHz. The peak directivity in each band is 18.2dBi and 20.5dBi, and the 3dB directivity bandwidth of each band is 7.5% and 8.7%, respectively.

Birefringence-induced mode-dependent tuning of liquid crystal infiltrated InGaAsP photonic crystal nanocavities

Mode-dependent shifts of resonant frequencies of cavities in liquid crystal (LC) infiltrated planar photonic crystals (PhC) are experimentally observed when the temperature is varied across the LC ordering transition. The shifts can be in opposite directions, even for two very similar nearly degenerate modes. The behavior is attributed to the different interactions of the modes with the two components of the refractive index of the LC infill and directly demonstrates that at least a substantial amount of the LC is oriented perpendicular to the PhC-hole axis.

Quasi-monolithic ring resonator for efficient frequency doubling of an external cavity diode laser

A quasi-monolithic second-harmonic-generation ring resonator assembled with miniaturized components is presented. The ring contains a 10-mm-long bulk periodically poled lithium niobate crystal for second-harmonic generation, four plane mirrors and two gradient-index lenses. All parts are mounted on a glass substrate with an overall size of 19.5 mm×8.5 mm×4 mm. As pump source a broad-area laser diode operated in an external resonator with Littrow arrangement is utilized. This external cavity diode laser provides near diffraction limited, narrow-bandwidth emission with an optical output power of 450 mW at a wavelength of 976 nm. Locking of the diode laser emission to the resonance frequency of the ring cavity was achieved by an optical self-injection locking technique. With this setup more than 126 mW of diffraction-limited blue light at 488 nm could be generated. The opto–optical conversion efficiency was 28% and a wall plug efficiency better than 5.5% could be achieved.

Laboratory Test of the Isotropy of Light Propagation at the10−17Level

We report on the results of a strongly improved test of local Lorentz invariance, consisting of a search for an anisotropy of the resonance frequencies of electromagnetic cavities. The apparatus comprises two orthogonal standing-wave optical cavities interrogated by a laser, which were rotated approximately 175 000 times over the duration of 13 months. The measurements are interpreted as a search for an anisotropy of the speed of light, within the Robertson-Mansouri-Sexl (RMS) and the standard model extension (SME) photon sector test theories. We find no evidence for an isotropy violation at a 1sigma uncertainty level of 0.6 parts in 10(17) (RMS) and 2 parts in 10(17) for seven of eight coefficients of the SME.

Resonance frequencies of cavities in three-dimensional electromagnetic band gap structures

This paper is devoted to the phenomenon of resonant transmission in three-dimensional electromagnetic band gap structures (EBGs), achieved by introducing a defect into an EBG structure with the corresponding resonance frequency of the defect lying within the initial EBG region. It is shown that the resonance frequency of an EBG air cavity (acceptor defect) can either increase or decrease with increasing cavity dimensions. In particular, this paper demonstrates both experimentally and theoretically that the resonance frequency of a woodpile air cavity, formed by the partial removal of a woodpile bar, increases with increasing cavity size; it increases continuously or saturates depending on the field polarization with respect to the cavity orientation. The results obtained in this paper can be used for designing EBG devices based on resonant transmission.

The dynamical Casimir effect and resonance frequency shifts in cavities with thin photo-excited semiconductor layers

I derive a new formula (generalizing the Müller–Bethe–Schwinger–Casimir formula) for the shift of complex resonance frequency of an electromagnetic cavity due to strong variations of the complex dielectric function in a thin layer near an ideally conducting wall. This formula is used to predict a photon generation rate in recently proposed experiments on the dynamical Casimir effect.

Test of Lorentz invariance using optical cavities

This paper indroduces the precision test of Lorentz invariance using ultra-stable and low-loss optical cavities. The effective-field theory widely adopted in the analysis of experimental data has been reviewed. The sensitivity of the cavity resonant frequency to the Lorentz-violating tensor field is discussed in detail. In addition, the polarization of the optical field has been added to the model, and our analysis shows that the frequency shift due to Lorentz violation is not sensitive to the polarization of the optical field.

Investigation of I– V characteristics of Bi-2212 intrinsic Josephson junctions for THz-wave generation

Voltage jumps have been observed in the quasiparticle branch I– V characteristics of Bi 2Sr 2CaCu 2O 8+ x intrinsic Josephson junctions fabricated as 60 μm × 300 μm × 0.5 μm mesas. The Josephson frequency at the highest jump voltage was estimated to be 0.65 THz, close to the fundamental cavity resonance frequency of the transverse Josephson plasma mode. Numerical simulations using coupled sine-Gordon equations demonstrated voltage jumps similar to the above experimental results, which appeared in the I– V characteristics, and the electric field distribution at the highest jump voltage exhibited resonance in the junctions. Moreover, the maximum radiation power, which was obtained in the vicinity of the highest voltage, was proportional to the square of the number of junctions. This can be explained by reduction of the impedance mismatch between the junctions and free space with increasing the number of junctions.

Design of input coupler for the superconducting cavity

The present paper describes in detail the design of the co-axial coupler for the high beta (∼0.42) 700 MHz superconducting cavity. It also describes the Kroll–Yu method for the computation of external Q. A copper prototype of cavity and co-axial coupler is fabricated and the measurement of external Q is carried out. A measured cavity resonant frequency was 694.9 MHz. The external Q was measured for the axial coupler by changing the penetration depth from −74.53 to −29.53 mm the external Q was varied from ∼1.03×10 6 to 1.38×10 3. The experimental results and the computational results match well.

Dynamical Casimir effect: Some theoretical aspects

This is a brief description of some recent achievements in the theory of dynamical Casimir effect, mainly in connection with the experiment which is under preparation in the University of Padua. The first part of this paper is devoted to the theory of quantum damped oscillator with arbitrary time dependence of the frequency and damping coefficient. New results for the mean number of created photons, its variance and photon distribution function are given. The second part is devoted to calculations of the time-dependent shift of resonance frequency of an electromagnetic cavity due to strong variations of dielectric properties in a thin layer near an ideally conducting wall. A simple analytical formula for this shift is derived. It generalizes the known Schwinger-Bethe-Casimir result. The influence of different parameters on the photon generation rate is discussed. A brief review of recent publications on the subject is also included.

Bandwidth and Dynamic Range of a Widely Tunable Josephson Parametric Amplifier

We characterize the signal bandwidth and dynamic range of a recently developed type of Josephson parametric amplifier. These amplifiers consist of a series array of SQUIDs embedded in a microwave cavity. They are narrow band, only amplifying signals close to the cavity's resonance frequency, but the cavity's resonance frequency, and hence the amplified band, can be widely tuned. For a particular realization of these amplifiers we measure how the signal bandwidth depends on amplifier's gain. We find that the amplitude gain times signal bandwidth is approximately the linewidth of the cavity. In addition we measure the amplifier's dynamic range and saturation power.

Flat broadband chaotic carrier generation and synchronization

The chaotic carrier with smooth spectrum and broad bandwidth is generated by a distributed feedback （DFB） semiconductor laser subject to unidirectional fiber ring optical feedback. The smooth spectrum of the obtained chaotic carrier hides the external cavity resonance frequency peak，therefore the security of the system is enhanced. By unidirectional coupling，we implement the stable chaos synchronization when the chaotic light is injected into a solitary DFB laser diode. The correlation coefficient of synchronization is 0.84. The effects of injection strength and optical frequency detuning on synchronization are investigated experimentally. The results show that in conditions of strong injected locking the synchronization can be achieved in a large range of frequency detuning，and the stronger injection corresponds to the larger range of frequency detuning in which chaos synchronization maintains. The synchronization quality improves with the injection strength increasing.