Fractional Order Theory in a Semiconductor Medium Photogenerated by a Focused Laser Beam

In this paper, the fractional order theory has been applied for thermal, elastic and plasma waves to determine the carrier density, displacement, temperature and stress in a semiconductor medium. The thermal, elastic and plasma waves in a semi-infinite medium photogenerated by a focused laser beam were analyzed. The Laplace transformation is used to express the governing equation and solved analytically by applying eigenvalue approach methodology in that domain. A semiconducting material like as silicon was considered. According to the numerical results and graphics, the fractional order parameter and thermal relaxation time may play an important role in the behavior of all physical quantities.     

Optical cavity resonance with magnetized plasma

Indefinite media with mixed signs of dielectric tensor elements possess unbounded equifrequency surfaces that have been utilized for diverse applications such as superimaging, enhanced spontaneous emission, and thermal radiation. One particularly interesting application of indefinite media is an optical cavity supporting anomalous scaling laws. In this Letter, we show that by replacing an indefinite medium with magnetized plasma one can construct a tunable indefinite cavity. The magnetized plasma model is based on realistic semiconductor material properties at terahertz frequencies that show hyperbolic dispersion in a certain frequency regime. The hyperbolic dispersion features are utilized for the design of optical cavities. Dramatically different sizes of cavities can support the same resonance mode at the same frequency. For a cavity of fixed size, the anomalous scaling law between the resonance frequency and mode number is confirmed. The resonance frequency can be strongly modulated by changing the strength of the applied magnetic field. The proposed model provides active controllability of terahertz resonances on the deep subwavelength scale with realistic semiconductor materials.     

A DPL model of photothermal interaction in a semiconductor material

The generalized model for plasma, thermal, and elastic waves under dual phase lag model have been applied to determine the carrier density, the displacement, the temperature, and the stresses in a semiconductor medium. Using Laplace transform and the eigenvalue approach methodology, the solutions of all variables have been obtained analytically. A semiconducting material like as silicon was considered. The results were graphically represented to show the different between the dual phase model, Lord and Shulman’s theory and the classical dynamical coupled theory.     

A Helmholtz resonator buried in the ground as a source of seismic waves and low-frequency sound in the atmosphere

The procedure is given for calculating the total power of low-frequency sound and seismic waves produced by a Helmholtz resonator in the form of an air-filled spherical cavity buried in the ground and supplied with a hole through which it is connected with the atmosphere. The sound is generated by air oscillations in the resonator’s neck section that is open to the atmosphere, while the compression and shear elastic waves are generated in the bulk of the ground by cyclic pressure fluctuations that act on the spherical walls of the cavity. Calculations show that the coincidence of the resonance frequencies (within approximately ten to hundred hertz), at which both the sound radiation to the atmosphere and the elastic seismic radiation in the form of longitudinal and transverse bulk waves are maximum, can occur only when the resonator is placed in a loose ground characterized by reduced elastic characteristics. In these conditions, the power of transverse waves exceeds the sound power by a factor of two and the power of longitudinal waves is smaller than the sound power by a factor of several tens.     

Resonant tunnelling in photonic microcavities: design of highly directive radiating systems

The origins of the directivity and frequency selectivity of radiating sources embedded in photonic microcavities are examined. We start from a quasi-1D approach for unbounded systems which, by analogy with resonant tunnelling processes in semiconductor superlattices, gives us the intrinsic relationships between angular and frequency properties of the radiating system. The cavity design in a three-dimensional configuration and the consequences of the openness of the system on the radiation properties are addressed. It is shown that the evanescence properties of the electromagnetic waves within cavity walls associated with a unitary transmission induced by a resonant defect mode of a symmetric structure are key parameters in the design of a highly directive radiating system.     

Effect of thermal stresses on the phase transition temperature in a ferroelectric-dielectric nanocomposite

The mechanism of an increase in the phase transition temperature of a ferroelectric-dielectric nanocomposite above the corresponding temperature of an unbounded homogeneous ferroelectric has been revealed. The significant thermal stresses induced in the composite material due to the difference in the thermal and elastic characteristics of its components affect the polarized state of the ferroelectric component via the electrostrictive coupling and can lead to an increase in the phase transition temperature of the composite.     

Dynamic viscoelastic effects on sound wave scattering by an eccentric compound circular cylinder

The classical method of separation of variables in conjunction with the translational addition theorem for cylindrical wave functions are employed to obtain an exact solution for two-dimensional interaction of a harmonic plane acoustic wave with an infinitely long (visco)elastic circular cylinder which is eccentrically coated by another (visco)elastic material and is submerged in an ideal unbounded acoustic medium. The novel features of Havriliak-Negami model for dynamic viscoelastic material behaviour are used to take the rheological properties of the coating (and/or core) material into consideration. The analytical results are illustrated with numerical examples in which a steel rod eccentrically coated with (an eccentric steel shell filled with) dissipative materials of distinct viscoelastic properties is insonified by plane sound waves at selected angles of incidence. The effects of incident wave frequency, angle of incidence, core eccentricity and dynamic viscoelastic material properties on the backscattered form function spectra are examined. Limiting cases are considered and fair agreements with available solutions are obtained.     

Influences of interfacial damage on the effective wave velocity in composites with reinforced particles

The scattering of elastic waves by a spherical particle with imperfect interface and the multiple scattering by many spherical particles with imperfect interface are studied in this paper. First, the scattering of elastic waves by a spherical particle with imperfect interface, i.e. spring interface model, is studied. Then, the multiple scattering by random distributed particles with interfacial damage in a composite material is investigated. The equations to evaluate velocity and attenuation of effective waves defined by statistic averaging are given. Furthermore, based on the established relation between the effective velocity and interfacial constants, a method to evaluate the interfacial damage nondestructively from the ultrasonic measure data is proposed. The numerical simulation is performed for the Sic-Al composites. The effective velocity is computed to show the influences of interface damage. By using the genetic algorithm, the interfacial damage is evaluated from the synthetic experimental data with various levels of error. The numerical results show the feasibility of the method proposed to approximately evaluate the interfacial damage in a composite material with reinforced particles based on ultrasonic data. Supported by the National Natural Science Foundation of China (Grant Nos. 10672019 and 10272003)     

Semiconductor disk lasers for the generation of visible and ultraviolet radiation

Recent developments in semiconductor disk lasers (SDLs) generating visible or ultraviolet light are reviewed. After an introduction on potential applications, we discuss how the combination of vertical‐emitting semiconductor GaAs‐based structures and intra‐cavity nonlinear conversion techniques can be successfully exploited to uniquely meet demands for continuous‐wave radiation in the visible and ultraviolet spectral range. To do so, an overview of the device operating principles and performance is presented highlighting the underlying material considerations, semiconductor structural designs, thermal management techniques and suitable cavity configurations. This summary is completed by a presentation of new developments in the field, with a particular focus on the trends towards miniaturization.     

Love wave propagation in piezoelectric layered structure with dissipation

We investigate analytically the effect of the viscous dissipation of piezoelectric material on the dispersive and attenuated characteristics of Love wave propagation in a layered structure, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of the viscous coefficient on the phase velocity of Love waves and attenuation are presented and discussed in detail. The analytical method and the results can be useful for the design of the resonators and sensors.     

Parametric scattering of high-frequency elastic waves by a small spherical cavity oscillating under the action of a Rayleigh wave

Scattering of high-frequency transverse and longitudinal plane waves incident on a spherical cavity located at a small depth under the surface of a half-space is considered. The cavity oscillates as a whole in the field of a low-frequency Rayleigh surface wave, the oscillation vectors of the longitudinal, transverse, and surface waves being coplanar. The cavity radius is assumed to be small compared to the wavelengths of the sounding wave and the pumping surface wave. The scattered compression and shear waves at the combination frequencies ω±Ω are calculated in the dipole approximation. Expressions obtained describe the qualitative behavior of the combination-frequency signal levels produced at the outputs of horizontally and vertically oriented geophones moving over the free surface of the elastic half-space.     

A theoretical study of hot plasma spheroids in the presence of low-frequency electromagnetic waves

While taking into account thermal motion of electrons, scattering of electromagnetic waves with low frequency from hot plasma spheroids is investigated. In this theoretical research, ions are heavy to respond to electromagnetic fluctuations. The solution of scalar wave equation in spheroidal coordinates for electric potential inside the plasma spheroids are obtained. The variations of resonance frequencies vs. Debye length are studied and consistency between the obtained results in this paper and the results for the well-known plasma objects such as plasma column and spherical plasma have been proved.     

Radiation from an Electric Dipole Surrounded by a Plasma Cylinder with a Cavity

We solve the problem of the influence of a small-radius (ka1) isotropic plasma cylinder with a coaxial free-space cavity on the radiation from a source of electromagnetic waves to an outer region of free space. Conditions of the resonance radiation are obtained and characteristics of this radiation as functions of the relative size of the cavity are studied. We show that the resonance frequency splits into two frequencies such that the transmission coefficients at these frequencies can exceed the resonance transmission coefficient for the plasma cylinder without a cavity. The results obtained are compared with the case of emission from a two-layer spherical plasma resonator.     

Effective wave numbers for thermo-viscoelastic media containing random configurations of spherical scatterers

The dispersion relation is derived for the coherent waves in fluid or elastic media supporting viscous and thermal effects and containing randomly distributed spherical scatterers. The formula obtained is the generalization of Lloyd and Berry's [Proc. Phys. Soc. London 91, 678-688 (1967)], the latter being limited to fluid host media, and it is the three-dimensional counterpart of that derived by Conoir and Norris [Wave Motion 47, 183-197 (2010)] for cylindrical scatterers in an elastic host medium.     

Simultaneous unidirectional reciprocal filters of electromagnetic and elastic waves based on the modal symmetry of phoxonic crystal waveguides and cavity

We theoretically achieve the simultaneous unidirectional reciprocal filter of electromagnetic (EM) and elastic waves in a single phoxonic crystal by the finite-element method. The functionality is achieved by matching and mismatching the modal symmetry between a resonant cavity and two mutually perpendicular waveguides. Suitable phoxonic cavity and waveguides are created to realize the match and mismatch of the modal symmetry for both EM and elastic waves. The proposed device has the abilities of phoxonic unidirectional filtering as well as providing great potential for enhancing acousto-optic coupling by simultaneously tailoring electromagnetic and elastic waves with an ultracompact footprint size.     

Helmholtz水声换能器弹性壁液腔谐振频率研究

针对传统Helmholtz水声换能器设计中刚性壁假设的局限性,将Helmholtz腔体的弹性计入到液腔谐振频率计算中,实现低频弹性Helmholtz水声换能器液腔谐振频率精确设计.基于细长圆柱壳腔体的低频集中参数模型,导出了腔体弹性引入的附加声阻抗表达式,得到了弹性壁条件下Helmholtz水声换能器等效电路图,给出了考虑了末端修正的弹性壁Helmholtz共振腔液腔谐振频率计算公式.利用ANSYS软件建立了算例模型,仿真分析了不同材质、半径、长度时的Helmholtz共振腔液腔谐振频率.结果对比表明弹性理论值与仿真值符合得很好,相比起传统的刚性壁理论计算结果,本文的弹性壁理论得出的液腔谐振频率值有所降低,与真实情况更加接近.本文的结论可以为精确设计低频弹性Helmholtz水声换能器提供理论支持.     

Slowness surfaces, ray velocity surfaces and phonon focussing in highT c superconductor crystals

This paper reports the results of the study of anisotropy in elastic wave propagation in single crystal superconducting BSCCO. The inverse and group velocities of elastic waves propagating in different directions have been computed and the corresponding slowness and ray velocity surfaces plotted, taking elastic constant data from literature. In addition, the phenomenon of phonon focussing has been investigated in this material by computing the phonon enhancement factor along different directions in spherical polar coordinates. The abnormally high values in phonon enhancement factor exhibited in certain directions for the phonon modes are interpreted as due to caustics occurring in the geometrical acoustics approximation adopted in the computational analysis. The results in LSCO and YBCO are found to be similar to those in BSCCO.     

Accurate monoenergetic electron parameters of laser wakefield in a bubble model

A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal model and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. As a result, the quasi-mono-energetic electrons output beam interacting with the laser plasma can be more appropriately described with this model.     

高精细度光学参考腔的自主化研制

高精细度超稳光学参考腔是获得超窄线宽激光的核心部件.本文报道了面向空间应用的高精细度球形超稳光学参考腔自主化研制及其初步测试结果.设计球形腔体直径为80 mm,腔长78 mm,采用平-凹腔镜结构,凹镜曲率半径为0.5 m.使用有限元方法计算了该参考腔的震动敏感度,最佳支撑位置的震动敏感度小于1×10~(-10)/g.采用超光滑表面三级抛光技术实现光学表面粗糙度小于0.4 nm(rms)的超精密加工,采用双离子束溅射法实现工作波长反射率大于99.999%、损耗小于4 ppm腔镜镀膜,干式光胶方法键合腔体和腔镜.利用扫腔线宽法和腔衰荡法对参考腔的线宽和精细度进行了测量,结果表明该参考腔的精细度约为195000,线宽为9.8 kHz.将698 nm半导体激光器锁定到该参考腔上测得其损耗5 ppm.与实验室进口同类型参考腔相比较,主要性能指标与其相当.     

激光辐照引起的材料温度场和热应力场的瞬态分布

 光电探测器吸收激光后的温升以及因温升造成的各种现象,致使探测器遭受到不同程度的损伤。利用热弹性理论对CO2激光器辐照K9玻璃材料进行研究,建立激光辐照材料温升及热应力分布二维平面模型,通过解析计算得到由激光辐照半导体材料引起的温度场和应力场的瞬态分布。研究表明, K9玻璃材料的激光辐照损伤阀值与辐照时间和光斑半径相关。在同一条件下,造成的热应力损伤阀值较熔融损伤的低,故K9玻璃材料的破坏形态为热应力破坏。