Quantum dynamics of a mechanical resonator driven by a cavity

We explore the quantum dynamics of a mechanical resonator whose position is coupled to the frequency of an optical (or microwave) cavity mode. When the cavity is driven at a frequency above resonance the mechanical resonator can gain energy and for sufficiently strong coupling this results in limit-cycle oscillations. Using a truncated Wigner function approach, which captures the zero-point fluctuations in the system, we develop an approximate analytic treatment of the resonator dynamics in the limit-cycle regime. We find that the limit-cycle oscillations produced by the cavity are associated with rather low levels of energy fluctuations in the resonator. Compared to a resonator at the same temperature which is driven by a pure harmonic drive to a given average energy, the cavity-driven oscillations can have much lower energy fluctuations. Furthermore, at sufficiently low temperatures, the cavity can drive the resonator into a non-classical state which is number-squeezed.     

Three-mode optomechanical system for angular velocity detection

We propose a scheme for measuring the angular velocity of absolute rotation using a three-mode optomechanical system in which one mode of the two-dimensional(2 D) mechanical resonator is coupled to an optical cavity. When the total system rotates, the Coriolis force acting on the 2 D mechanical resonator due to the absolute rotation will affect the mechanical motion and thus change the phase of the output field from the cavity. The angular velocity of the absolute rotation can be estimated by monitoring the spectrum of the output field from the cavity via homodyne measurement. The minimum measurable angular velocity, which is determined by the noise spectrum, is calculated. The working range of the gyroscope for measuring angular velocity is discussed.     

基于同轴TM812模谐振腔的毫米波多注速调管

 研究了群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率和同轴TM₈₁₂模谐振腔中微波能量的提取方法,论证了其作为毫米波多注速调管的输出腔的可行性。研究结果表明:理想群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达3.29%,一般群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达1.86%;采用同轴TM₈₁₂模谐振腔与沿轴向的同轴线耦合可以实现微波能量的提取;在输出腔工作频率为100.945 GHz,外观品质因数为2 243情形下,根据估算,最大输出功率可达15 kW。     

Axion detection with negatively coupled cavity arrays

Using eigenmode analysis and full 3D FEM modelling, we demonstrate that a closed cavity built of an array of elementary harmonic oscillators with negative mutual couplings exhibits a dispersion curve with lower order modes corresponding to higher frequencies. Such cavity arrays may help to achieve large mode volumes for boosting sensitivity of the axion searches, where the mode volume for the composed array scales proportional to the number of elements, but the frequency remains constant. The negatively coupled cavity array is demonstrated with magnetically coupling coils, where the sign of next-neighbour coupling (controlled with their chirality) sets the dispersion curve properties of the resonator array medium. Furthermore, we show that similar effects can be achieved using only positively coupled cavities of different frequencies assembled in periodic cells. This principle is demonstrated for the multi-post re-entrant system, which can be realised with an array of straight metallic rods organised in chiral structures.     

锥形光纤激发盘腔光学模式互易性研究

光学谐振腔由于其高Q值特性,作为谐振式陀螺的核心元件,有望实现谐振式陀螺的小型化、集成化,但是非互易性噪声成为制约其精度提高的不利因素. 介绍了采用传统半导体工艺制备的盘型腔与熔融法拉制的锥形光纤组成的耦合系统. 当盘型腔在光纤锥区的不同位置进行耦合谐振时,将输入输出正/反对调,观察到输出透射谱发生偏差,谐振频率、耦合效率以及Q值均发生变化,即存在非互易性现象. 用Rsoft软件对锥形光纤倏逝场分布特性进行仿真,理论分析了非互易性产生的原因. 以此可抑制谐振式光学陀螺应用中由锥形光纤与谐振腔组成的耦合系统产生的非互易性噪声. 关键词： 光学谐振腔 锥形光纤 非互易性 谐振式陀螺     

Nonlinear quantum dynamics of two BEC modes dispersively coupled by an optical cavity

We derive a quantum master equation for a single mode excitation of a Bose-Einstein condensate by a high-finesse optical cavity. This system is formally analogous to a broad class of opto-mechanical systems comprising vibrating mirrors and resonator modes coupled by radiation pressure. The presented equation accounts for the dissipative part of the dynamics due to the coupling of a driven, lossy optical mode of a resonator. This allows for exploring the quantum limit of opto-mechanical systems in the presence of dissipation in a classically bistable regime. We find that the measurement-induced back-action noise impedes the observation of quantum tunneling and leads to a non-exponential dephasing of coherent matter wave oscillations.     

Microwave frequency modulation in CW EPR at W-band using a loop-gap resonator

Loop-gap resonator (LGR) technology has been extended to W-band (94GHz). One output of a multiarm Q-band (35GHz) EPR bridge was translated to W-band for sample irradiation by mixing with 59 GHz; similarly, the EPR signal was translated back to Q-band for detection. A cavity resonant in the cylindrical TE011 mode suitable for use with 100 kHz field modulation has also been developed. Results using microwave frequency modulation (FM) at 50 kHz as an alternative to magnetic field modulation are described. FM was accomplished by modulating a varactor coupled to the 59 GHz oscillator. A spin-label study of sensitivity was performed under conditions of overmodulation and gamma2H1(2)T1T2<1. EPR spectra were obtained, both absorption and dispersion, by lock-in detection at the fundamental modulation frequency (50 kHz), and also at the second and third harmonics (100 and 150 kHz). Source noise was deleterious in first harmonic spectra, but was very low in second and third harmonic spectra. First harmonic microwave FM was transferred to microwave modulation at second and third harmonics by the spins, thus satisfying the "transfer of modulation" principle. The loaded Q-value of the LGR with sample was 90 (i.e., a bandwidth between 3 dB points of about 1 GHz), the resonator efficiency parameter was calculated to be 9.3 G at one W incident power, and the frequency deviation was 11.3 MHz p-p, which is equivalent to a field modulation amplitude of 4 G. W-band EPR using an LGR is a favorable configuration for microwave FM experiments.     

Cold tests of A 10-GHz gyrotron cavity

Experiments have been conducted to characterize a gyrotron cavity designed to operate in theTE ₀₂₁ mode at 10 GHz. Cavity excitation was accomplished via a coupling hole introduced into the cavity wall and mode detection was carried out by means of two experimental arrangements. In the first, electromagnetic energy is coupled into a receiving waveguide through a small second hole drilled in the opposite side of the cavity. The other scheme uses a horn antenna to receive the power reradiated by the open resonator. Both schemes are discussed regarding mode detection, and measured data includes resonant frequency, loadedQ factor, axial electric field profile and farfield radiation pattern. Evaluation of the loadedQ factor is based on bandwidth measurements whereas standing-wave electric field profile is determined by using perturbation techniques. For severalTE modes, close agreeent between theory and experiment is found.     

Excitation of orotron oscillations at the doubled frequency of a surface wave

We study theoretically an electron frequency self-multiplier in which a surface mode of a periodic system is self-excited at a low frequency for a comparatively low current. The electron bunches, which appear as a result of this, excite the volume mode of an open resonator at the doubled frequency (coherent Smith-Purcell radiation). The open-resonator scheme allows one to obtain the higher power and coherence degree of radiation compared with the presently popular frequency multiplication scheme with an open periodic system (diffraction grating). The weakly relativistic and relativistic variants of the multipliers with a two-mirror open resonator designed for obtaining a high-power coherent radiation in the short-wavelength part of the millimeter and submillimeter ranges are studied numerically. The developed approach can also be used for designing high-power frequency multipliers on the basis of an array of nonlinear solid-state elements.     

Compact cavity resonators using high impedance surfaces

This paper presents a miniaturization concept for cavity resonators. The idea is to create a λ/4 long cavity resonator by using a combination of Perfect Electric Conductor (PEC) and Perfect Magnetic Conductor (PMC) boundary conditions. Reducing by half the length and width of a metallic cavity resonator and placing PMC boundary conditions on two adjacent side walls allows the resonance of a λ/4 mode inside the hybrid cavity resonator, at the same frequency as the λ/2 long metallic one. The practical implementation of the PMC boundary condition is realized by using High Impedance Surfaces (HIS). The design of the surfaces is realized at the element level and is implemented on standard microwave substrate. Measurements demonstrate a cavity resonator operating at 4 GHz with half the length and width of a metallic cavity resonator, meanwhile its volume is divided by four.     

ac Stark shift and dephasing of a superconducting qubit strongly coupled to a cavity field

We have performed spectroscopy of a superconducting charge qubit coupled nonresonantly to a single mode of an on-chip resonator. The strong coupling induces a large ac Stark shift in the energy levels of both the qubit and the resonator. The dispersive shift of the resonator frequency is used to nondestructively determine the qubit state. Photon shot noise in the measurement field induces qubit level fluctuations leading to dephasing which is characteristic for the measurement backaction. A crossover in line shape with measurement power is observed and theoretically explained. For weak measurement a long intrinsic dephasing time of T2>200 ns of the qubit is found.     

Normal mode splitting and ground state cooling in a Fabry-Perot optical cavity and transmission line resonator

Optomechanical dynamics in two systems which are a transmission line resonator and Fabrya-Perot optical cavity via radiation-pressure are investigated by linearized quantum Langevin equation. We work in the resolved sideband regime where the oscillator resonance frequency exceeds the cavity linewidth. Normal mode splittings of the mechanical resonator as a pure result of the coupling interaction in the two optomechanical systems is studied, and we make a comparison of normal mode splitting of mechanical resonator between the two systems. In the optical cavity, the normal mode splitting of the movable mirror approaches the latest experiment very well. In addition, an approximation scheme is introduced to demonstrate the ground state cooling, and we make a comparison of cooling between the two systems dominated by two key factors, which are the initial bath temperature and the mechanical quality factor. Since both the normal mode splitting and cooling require working in the resolved sideband regime, whether the normal mode splitting influences the cooling of the mirror is considered. Considering the size of the mechanical resonator and precooling the system, the mechanical resonator in the transmission line resonator system is easier to achieve the ground state cooling than in optical cavity.     

Observation of spectral modulation coupled with broadband transverse-mode-locking in an Yb:CALGO frequency-degenerate cavity

A frequency-degenerate cavity(FDC) is the resonator that the ratio of transverse and longitudinal mode frequency spacings is a simple rational number. When an optical resonator is close to the FDC, transverse-mode-locking(TML) takes place with drastic changes of laser mode. We report for the first time, to the best of our knowledge,the multi-frequency emission and spectral modulation effects coupled with TML in FDC. The Yb:CaGdAlO_4(Yb:CALGO) crystal with large gain bandwidth was used as a gain medium in an off-axis-pumped hemispherical FDC for realizing broadband emission. Interestingly, the spectrum can transform from a single smooth packet shape to a multi-peak structure; meanwhile, the transverse pattern accordingly transforms into some exotic wave-packet profiles through controlling off-axis displacement in a special degenerate state.     

Squeezing by second-harmonic generation in a monolithic resonator

We have measured the intensity fluctuations of the second-harmonic mode generated in a MgO:LiNbO₃ external monolithic cavity pumped by a Nd:YAG laser. The cavity has mirror coatings for both the fundamental and the second-harmonic mode. We scan the cavity using the electro-optic effect of the crystal and observe that the second-harmonic beam of 2 mW exhibits a quantum noise reduction of 40(±5)%. In addition, we report on the active frequency stabilization of the monolithic device used in our squeezing experiments. Several fast tuning parameters such as the electro-optic effect, the photo-elastic effect, and the laser frequency have been investigated. With these tuning parameters the monolithic resonator can be locked on double-resonance at the phase-matching temperature, which is a prerequisit for observing squeezing in a cw-regime.     

Helmholtz腔与弹性振子耦合结构带隙

为提高Helmholtz型声子晶体低频隔声性能,设计了一种Helmholtz腔与弹性振子的耦合结构,通过声压场及固体振型对其带隙产生机理进行了详细分析,建立了相应的弹簧-振子系统等效模型,并采用理论计算和有限元计算两种方法研究了各结构参数对其带隙的影响情况.研究表明,该结构可等效为双自由度系统振动,在低频范围内具有两个带隙;在6 cm的尺寸下,其第一带隙下限可低至24.5 Hz,而同尺寸无弹性振子结构只能达到42.1 Hz,带隙下限降低了40%,较传统Helmholtz结构具有更为优良的低频隔声特性.另外,在框体尺寸一定的情况下,降低结构间距、增大开口空气通道长度及振子质量、增大左侧腔体体积等方式,是增大带隙宽度、提高低频隔声效果的主要手段.     

高斯光束与谐振腔基模模式光路谐振匹配的分析与校准

为了降低高斯光束与谐振腔耦合过程中失调量和失配量对基于无源谐振腔测量技术精度的影响, 采用高斯光束变换规律、模式耦合有关理论以及光束传播坐标变换等相关理论, 就失调量和失配量对基模耦合效率的影响分别进行分析和模拟, 并据此给出了一般情况下两个参考量同时存在时基模耦合效率的表达式. 分析表明: 失配量的存在主要影响激光器与谐振腔的耦合效率, 而对高阶模式的激发影响较小, 因此对谐振腔的衰减线型影响较小; 失调量的存在对谐振腔高阶模式的激发起主要作用, 给测量带来严重误差. 该结论为利用腔出射光信号来确定误调参量值的实验方案提供了依据. 因此, 在考虑光源光谱线宽的情况下, 就光源光谱线宽的特性提出两种装调校准方案: 基于法布里-珀罗干涉仪法和基于多维象限探测器探测谐振腔出射光的调节回路, 这将为分析基于无源谐振腔的相关技术测量误差来源以及实现测量系统的高精度装调提供理论指导.     

Axial mode tuning of a single frequency Yb:YAG thin disk laser

We describe an arrangement for an Yb:YAG thin disk laser, which enables narrow bandwidth operation in single-frequency mode at freely selectable wavelengths within the broad tuning range of the laser. This is facilitated by a combination of a double-stage birefringent filter and an etalon inside the laser cavity. We investigate the wavelength selection characteristics of the single elements as well as their combination. A simple procedure is implemented for a computer-based automation of wavelength tuning. The reflectivity of the partially reflecting resonator mirror is optimised, and the laser pump power is adapted for best tuning performance. Single-frequency emission is achieved in a frequency range of 9.75 THz (wavelength range 1020 nm to 1055 nm). Each axial laser mode in this range can be selected individually. The axial mode separation of 0.47 GHz corresponds to wavelength steps of 1.7 pm at 1030 nm. PACS 42.55.Xi; 42.60.Fc; 42.60.Lh     

基于平面光波导谐振腔的可调谐光电振荡器

提出了一种基于平面光波导谐振腔的可调谐光电振荡器.该振荡器中,相位调制器串联光波导谐振腔,取代了传统系统中的强度调制器、长光纤和滤波器.由于光学谐振腔对光子频率和相位敏感,调节激光器改变输出光的波长,不仅可以调制光的强度,还可以对微波光子进行选频输出.当光子在波导腔中发生谐振时,产生很强的延时特性,可以取代传统系统中的长光纤.整个光电振荡器系统体积为长29.5cm、宽21cm、高7cm.实验中,改变0.1pm的光子波长,能够产生步长为12.535.5 MHz的调谐,调谐范围达2 GHz,且系统能够产生10 GHz的微波信号,在中心频率为10 GHz处其相位噪声为-109.7dBc/Hz@10kHz.该研究为光电振荡器的小型化和实用化提供了一种新的思路.     

Noise control of a rectangular cavity using macro perforated poro-elastic materials

The effectiveness of macro perforated porous materials to control noise levels inside a cavity is investigated. This is done using a finite element formulation based on the Biot-Allard theory that accounts for sound propagation in a poro-elastic medium. Earlier investigations have shown that macro-holes in a porous material can enhance low frequency sound absorption. However, this has been demonstrated in free field or waveguide environments. When such an approach is used in a cavity, it is seen that only certain patterns of macro-holes, dictated by cavity mode shapes, enhance noise reduction in the higher frequency ranges. This phenomenon is shown to be independent of porous material properties by considering two different materials. A correlation between the mode shapes and material removal is also established. A detailed convergence study for both cavity and poro-elastic finite element models, establishes the suitability of using higher order interpolation functions for coupled cavity-poro-elastic acoustic analysis.     

Tunable high-<Emphasis Type="Italic">Q</Emphasis> surface-acoustic-wave resonator

The feasibility of a tunable two-port surface-acoustic-wave resonator is analyzed theoretically and verified experimentally. The center frequency of the resonator is tuned by varying the equivalent length of its cavity. The variation of the center frequency achieved in the experiment is 25 kHz, with the width of the resonance peak being ≈4 kHz at a level of ?3 dB (the loaded Q factor of the resonator is ≈24600) and a frequency of ≈98 MHz. As a result of this study, a tunable resonator controlled by a static electric field that realizes the parameters predicted theoretically is designed. This resonator may serve as a basis for a stable tunable oscillator with a low phase noise.