Electrothermal oscillatory instability in ferroelectric resonators. Two-mode case

We consider the equations of interaction between electromagnetic oscillations and the temperature in a nonlinear dielectric resonator. The conditions for emergence of the oscillatory instability in the system are analyzed. The threshold conditions (power and automodulation frequency) of electrothermal excitation are calculated for microwave virtual-ferroelectric resonators for the simplest case of two-mode interaction. The dielectric nonlinearity is shown to impose limitations on the feasibility of electrothermal excitation. Physical Faculty, M. V. Lomonosov Moscow State University, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 2, pp. 162–173, September 2000.     

Parametric excitation of temperature oscillations in a high-Q dielectric microwave resonator in liquid helium vapor

We study the threshold conditions of the parametric excitation of temperature oscillations using pulsed microwave pumping in three-mode regime for high-Q ferroelectric cryogenic resonators made of SrTiO₃ and KTaO₃. Comparative analysis is performed for the threshold power of the excitation of temperature oscillations and the threshold power of the ponderomotive parametric excitation of acoustic oscillations in the resonator. It is shown that in three-mode regime, temperature oscillations can develop under a rather moderate pump power of about 0.1–8 μW, depending on the combination of interacting temperature and electromagnetic modes. The calculated low threshold powers allow one to apply resonators in practice as high-sensitivity infrared sensors, resonant bolometers, and parametric amplifiers. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 172–180, February 2009.     

Electrothermal Oscillatory Instability in Spherical Ferroelectric Resonators. Three-Mode Case

We consider the equations of interaction between electromagnetic oscillations and the temperature in a nonlinear dielectric resonator and study the dynamics of the oscillatory instability in the system. The threshold conditions (power and self-modulation frequency) of electrothermal excitation are calculated for microwave potassium-tantalate resonators for the case of three-mode interaction. The conditions for observing electrothermal excitation in the three-mode case are found to be quite favorable. In this case, the threshold power of excitation of temperature oscillations is smaller than that in the two-mode case and can amount to a few microwatts.     

Cryogenic Q-band (35GHz) probehead featuring large excitation microwave fields for pulse and continuous wave electron paramagnetic resonance spectroscopy: performance and applications

The construction and performance of a Q-band (35GHz) cryogenic probehead for pulse electron paramagnetic resonance and continuous wave electron paramagnetic resonance measurements with down-scaled loop gap resonators (LGRs) is presented. The advantage of the LGR in comparison to TE(012) resonators lies in the large B(1) microwave (mw) fields that can be generated with moderate input mw power. We demonstrated with several examples that this allows optimal performance for double-quantum electron coherence, HYSCORE, and hyperfine decoupling experiments employing matched and high turning angle mw pulses with high B(1)-fields. It is also demonstrated that with very low excitation power (i.e. 10-40 mW), B(1)-fields in LGRs are still sufficient to allow short mw pulses and thus experiments such as HYSCORE with high-spin systems to be performed with good sensitivity. A sensitivity factor Lambda(rs) of LGRs with different diameters and lengths is introduced in order to compare the sensitivity of different resonant structures. The electromagnetic field distribution, the B(1)-field homogeneity, the E(1)-field strength, and the microwave coupling between wave guide and LGRs are investigated by electromagnetic field calculations. The advantage and application range using LGRs for small sample diameters is discussed.     

Energy characteristics of photothermal vibrational instability at stimulated Raman and Mandelstam-Brillouin scattering in aerosol droplets

The threshold intensity and the combination frequencies for photothermal vibrational instability in high-Q aqueous aerosol droplets in the two-mode regime have been calculated. The selection rules for coupling electromagnetic and temperature modes in a droplet are obtained. A comparative analysis of the threshold excitation intensities of photothermal vibrational instability, stimulated Mandelstam-Brillouin scattering, and stimulated Raman scattering in droplets is performed. It is shown that photothermal vibrational instability in the two-mode regime can be developed at a pump intensity of about 10⁴ W/cm² for droplets with radii of 2–20 μm for a pump wavelength of 0.532 μm. A method of remote measurement of the microphysical droplet parameters from the additional periodic temperature shift of droplet eigenfrequencies in the spectrum of stimulated Raman scattering and lasing is proposed.     

Dielectric half-disk resonator with whispering-gallery modes for measurements of the electric properties of water

We study experimentally the possibility of measuring the dielectric properties of water in the millimeter wavelength range using dielectric resonators excited at the whispering-gallery modes. The influence of various conditions for excitation of such resonators by a local source on the sensitivity and resolution of the performed measurements is shown. Electrodynamic characteristics of the dielectric resonator as a cell for measurements of the electric properties of water are studied. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 9, pp. 769–776, September 2008.     

Resonance parametric excitation of temperature oscillations in levitating aerosol droplets

The threshold conditions of excitation of temperature oscillations in high-Q water aerosol droplets have been studied under the conditions of slow evaporation. Selection rules have been obtained for interacting modes in a droplet. The threshold intensity of excitation of temperature oscillations has been analyzed in comparison with the threshold intensity of stimulated Brillouin and stimulated Raman scattering in a droplet. It is shown that, in the three-mode regime, the temperature oscillations can be excited at a rather low pumping level (about 10 W/cm²). A method is proposed for the remote measurement of the microphysical parameters of a droplet from the periodic temperature shift of eigenfrequencies of a droplet, the threshold intensity of excitation of temperature oscillations, and the thermal Raman frequency.     

Defect-induced whispering-gallery-mode resonances in optical microdisk resonators

In this Letter we present results of theoretical and experimental studies of whispering-gallery modes in optical microdisk resonators interacting with subwavelength dielectric particles. We predict theoretically and confirm by direct observations that, contrary to the generally accepted models, both peaks of the particle-induced doublet of resonances are redshifted with respect to the position of the initial resonance.     

Whispering-gallery modes in a barrel-shaped dielectric resonator

We experimentally study a new type of resonator, namely, a barrel-shaped dielectric resonator with whispering-gallery modes which is formed by the cutting dielectric hemisphere. Compared with a hemispherical dielectric resonator, the E type oscillation spectrum of such a resonator is rarefied with respect to the azimuthal index. Comparative analysis of the electromagnetic characteristics of the barrel-shaped dielectric resonator and half-disk dielectric resonators shows that the radiation losses of the mode energy from the spherical surface are smaller than those from the cylindrical surface. This fact stimulates the high values of the internal Q-factor of modes of the barrel-shaped dielectric resonator. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 12, pp. 1041–1048, December 2005.     

Directional tunneling escape from nearly spherical optical resonators

We report the surprising observation of directional tunneling escape from nearly spherical fused-silica optical resonators, in which most of the phase space is filled with nonchaotic regular trajectories. Experimental and theoretical studies of the dependence of the far-field emission pattern on both the degree of deformation and the excitation condition show that nonperturbative phase-space structures in the internal ray dynamics profoundly affect tunneling leakage of the whispering-gallery modes.     

Pedestal antiresonant reflecting waveguides for robust coupling to microsphere resonators and for microphotonic circuits

Strip-line pedestal antiresonant reflecting waveguides are high-confinement, silica integrated optical waveguides in which the optical modes are completely isolated from the substrate by thin high-index layers. These waveguides are particularly well suited for whispering-gallery mode excitation in high-Q microspheres. They can also be used in microphotonic circuits, such as for microring resonators. The theory and design of these structures are highlighted. Experiments that show high coupling efficiency to microspheres are also demonstrated.     

Piezoelectric surface excitation and detection of GHz-sound waves using planar structures: Hertzian- and H-slot resonators

We report on experiments with two new kinds of microwave resonators for piezoelectric surface excitation of GHz-sound waves. These resonators consist of planar metal structures simply made by photolithography and especially suitable for the higher frequency range where the usual reentrant cavities can be applied no more due to mechanical fabrication difficulties. Moreover, by choosing an appropriate resonator geometry, an electric excitation field with preferred orientation can be generated which allows to enhance or to supress wanted sound modes simply by turning the crystal relative to the excitation structure into an optimum orientation.Supported by Deutsche Forschungsgemeinschaft     

太赫兹表面极化激元

作为束缚于表面或界面的电磁波与极性元激发的耦合模量子,表面极化激元是克服衍射极限的核心物理.在紫外、可见以及近红外波段,表面等离子极化激元展现出了亚波长特性,具有高分辨成像等应用,并发展成为"表面等离子极化激元亚波长光学"学科;在中红外波段,表面声子极化激元发挥着同样的作用.太赫兹波段曾是人类认识的空白区域,近三十年来得以高速发展,其战略意义重大.具有克服衍射极限能力的太赫兹表面极化激元同样是小型化与集成化太赫兹器件,以及太赫兹超高分辨成像的重要物理基础.近几年来,对以石墨烯为代表的二维材料的研究突飞猛进,诞生了"石墨烯表面等离子极化激元亚波长光学"这门学科,并贡献于太赫兹领域.本文对可在太赫兹波段工作的人工超构材料、掺杂半导体、二维电子气、二维材料、拓扑绝缘体等结构材料的表面极化激元进行了较为全面的总结与介绍,为研制克服衍射极限的太赫兹集成光子学器件提供可资借鉴的物理基础.     

Planar microresonators for EPR experiments

EPR resonators on the basis of standing-wave cavities are optimised for large samples. For small samples it is possible to design different resonators that have much better power handling properties and higher sensitivity. Other parameters being equal, the sensitivity of the resonator can be increased by minimising its size and thus increasing the filling factor. Like in NMR, it is possible to use lumped elements; coils can confine the microwave field to volumes that are much smaller than the wavelength. We discuss the design and evaluation of EPR resonators on the basis of planar microcoils. Our test resonators, which operate at a frequency of 14 GHz, have excellent microwave efficiency factors, achieving 24 ns pi/2 EPR pulses with an input power of 17 mW. The sensitivity tests with DPPH samples resulted in the sensitivity value 2.3 x 10(9) spins.G(-1) Hz(-1/2) at 300 K.     

Lindblad Dynamics and Disentanglement in Multi-Mode Bosonic Systems

In this paper, we consider the thermal bath Lindblad master equation to describe the quantum nonunitary dynamics of quantum states in a multi-mode bosonic system. For the two-mode bosonic system interacting with an environment, we analyse how both the coupling between the modes and the coupling with the environment characterised by the frequency and the relaxation rate vectors affect dynamics of the entanglement. We discuss how the revivals of entanglement can be induced by the dynamic coupling between the different modes. For the system, initially prepared in a two-mode squeezed state, we find the logarithmic negativity as defined by the magnitude and orientation of the frequency and the relaxation rate vectors. We show that, in the regime of finite-time disentanglement, reorientation of the relaxation rate vector may significantly increase the time of disentanglement.     

Observation of anomalous transmission modes in nickel at microwave frequencies

A study has been made of the transmission of energy through nickel crystals in magnetic fields up to 13 kG using incident microwave power at 9.37 GHz. The transmission spectrum has been studied as a function of temperature and magnetic field orientation relative to the sample surface. A new set of anomalous transmission modes has been observed with the field perpendicular to the sample plane; these modes cannot be explained within the framework of existing theoretical models describing the resonance excitation of sound in ferromagnetic metals by electromagnetic waves.     

纳米三明治结构光子超材料中电磁场振荡行为研究

对金属-介质-金属的三层纳米三明治结构中的磁性等离子体模式特性进行了时域有限差分数值计算分析,并给出该类谐振器的品质因数变化规律.基于纳米三明治结构中的磁性等离子体模式对该种结构进行设计,研究几何构型参数以及介质材料折射率对磁性等离子体模式的调控规律.以电感电容等效电路近似理论对纳米三明治结构磁性等离子体模式谐振频率的变化规律进行理论解释,理论解释与数值计算结果符合很好.同时还研究了纳米三明治振荡器对电磁能量的限制,并从热和辐射两方面分析了该类结构的品质因数变化情况,可为基于磁性等离子体模式的新型波导及激光器结构的设计提供指导.     

Generation of Einstein-Podolsky-Rosen-entangled radiation through an atomic reservoir

We propose a scheme for generating two-mode squeezing in high-Q resonators using a beam of atoms with random arrival times, which acts as a reservoir for the field. The scheme is based on four-wave mixing processes leading to emission into two cavity modes, which are resonant with the Rabi sidebands of the atomic dipole transition, driven by a saturating classical field. At steady state the cavity modes are in an Einstein-Podolsky-Rosen state, whose degree of entanglement is controlled by the intensity and the frequency of the transverse field. This scheme is robust against stochastic fluctuations in the atomic beam, does not require atomic detection nor velocity selection, and can be realized by presently available experimental setups with microwave resonators.     

Simulation of laser oscillation in a two-layer microcavity with a semiconductor nanostructure shell

A theoretical model that describes the transformation of electromagnetic radiation by microcavities in the form of microspheres with a semiconductor nanostructure shell is developed. It is established that the regime of bistable two-mode laser oscillation due to morphology-dependent resonances with different quality factors and spatial distributions of the electromagnetic field can be implemented in a two-layer microcavity with a semiconductor-nanostructure shell. The region of two-mode oscillation and the relation between the intensities of oscillating modes depend on the indices of refraction and the sizes of the microparticle core and shell.     

Crystal quartz optical whispering-gallery resonators

A quality factor exceeding 5x10(9) is obtained in whispering-gallery mode (WGM) resonators fabricated of crystalline quartz. We observe significant electrical tunability of WGMs in x-cut resonators and demonstrate an electro-optic modulator with a submegahertz passband at 12 GHz. We discuss other photonics applications of the crystal quartz WGM resonators in narrowband agile tunable filters, compact narrow linewidth lasers, and microwave and millimeter wave oscillators.