Single-beam trapping in front of reflective surfaces

We show that the optical trapping of dielectric particles by a single focused beam in front of a weakly reflective surface is considerably affected by interference of the incident and reflected beams, which creates a standing-wave component of the total field. We use the two-photon-excited fluorescence from a trapped dyed probe to detect changes in the distance between the trapped beam focus as the focus approaches the reflective surface. This procedure enables us to determine the relative strengths of the single-beam and the standing-wave trapping forces. We demonstrate that, even for reflection from a glass-water interface, standing-wave trapping dominates, as far as 5 mum from the surface.     

Laser-induced damage of 1064-nm narrow-band interference filters under different laser modes

The laser-induced damage behavior of narrow-band interference filters was investigated with a Nd:YAG laser at 1064 nm under single-pulse mode and free-running laser mode.The absorption measurement of such coatings has been performed by surface thermal lensing(STL)technique.The relationship between damage morphology and absorption under the two different laser modes was studied in detail.The explanation was given by the standing-wave distribution theory.     

两种反射膜系的激光热力损伤特性

 在驻波场理论基础上,用表面和界面强吸收理论模型,计算出了激光辐照下两种不同反射膜系中温度场的“多峰”分布特性,分析了激光对薄膜的热力损伤特性、主要破坏模式和阈值条件。结果表明,光学薄膜对激光能量的吸收,主要由驻波场分布及膜层的消光系数决定;膜系表面的杂质吸附层和界面吸收层是膜系的主要能量沉积区,从而在这些界面形成温度场的“多峰”分布,界面因此成为最容易受激光损伤的部分。导致光学薄膜激光损伤的主要模式为膜层熔融和脱落两种。如果膜层中含有杂质,则容易诱导杂质处膜层剥落破坏。     

Cavity-enhanced laser cooling of solid-state materials in a standing-wave cavity

We propose a new method to cool the yb^3＋-doped ZBLANP glass in a standing-wave cavity. There are two advantages of this cavity-enhanced technique： the pumping power is greatly enhanced and the absorption of the cooling material is greatly increased. We introduce the basic principle of the cavity-enhanced laser cooling and discuss the cooling effect of a solid-state material in a cavity. From the theoretical study, it is found that the laser cooling effect is strongly dependent on the reflectivity of the cavity mirrors, the length of the solid material, the surface scattering of the material, and so on. Some optimal parameters for efficient laser cooling are obtained.     

Experimental study of large-amplitude standing-wave field obtained in a standing-wave tube with uniform cross section

A large-amplitude standing-wave field of 182.1 dB is obtained under the excitation at the resonant frequency of the lst-order peak of the sound pressure transfer function in an improved standing-wave tube experimental system,and saturation of harmonics and waveform distortion are investigated experimentally for the large-amplitude standing-wave fields obtained under the excitations at the resonant frequencies of the 1 st-to the 5 th-order peaks.The results show that although the sound pressure level has reached 182.1 dB under the excitation at the resonant frequency of the 1 st-order peak,the waveform distortion is the minimum and the harmonic saturation is not observed.However,the large-amplitude standing-wave field excited at the resonant frequency of the 3 rd-order peak exhibits the trend of the harmonic saturation.Comparison of the large-amplitude standing-wave fields obtained under the excitations at valley resonant frequencies shows that the standing-wave field excited at the resonant frequency of the 1 st-order valley has the largest SPL,but also has the largest waveform distortion.Under the same source-driving voltage,the standing-wave field excited at the resonant frequency of the 1 st-order peak always has greater SPL than the standing-wave field excited at the resonant frequency of the 1 st-order valley.Hence,to obtain a large-amplitude standing-wave field,it's better to excite at the resonant frequency of the 1 st-order peak of the SPTF by using loudspeaker in a standing-wave tube with uniform cross section.     

Estimation of Plasma Density by Surface Plasmons for Surface-Wave Plasmas

An estimation method of plasma density based on surface plasmons theory for surface-wave plasmas is proposed. The number of standing-wave is obtained directly from the discharge image, and the propagation constant is calculated with the trim size of the apparatus in this method, then plasma density can be determined with the value of 9.1 × 10^17m^-3. Plasma density is measured using a Langmuir probe, the value is 8.1 × 10^17m^-3 which is very close to the predicted value of surface plasmons theory. Numerical simulation is used to check the number of standing-wave by the finite-difference time-domain （FDTD） method also. All results are compatible both of theoretical analysis and experimental measurement.     

失谐驻波管及其极高纯净驻波场性质的研究

由直径不同的两级直圆管连接而成的两级突变截面驻波管具有失谐性,即高阶共振频率不是一阶共振频率的整数倍. 两级突变截面驻波管的失谐性质能够很好地抑制一阶共振频率激励下的大振幅非线性驻波畸变产生的高次谐波,从而获得大振幅纯净驻波场. 通过对两级突变截面驻波管失谐性质的研究,采用大功率扬声器正接等措施,利用两级突变截面驻波管的失谐性质在一阶共振频率激励下获得了184 dB的极高纯净驻波场,并对二至五阶共振频率激励下的声场进行了相应的实验研究. 在二阶、四阶共振频率激励下分别获得了180和166 dB波形比较规整的大振幅非线性驻波,并在三阶、五阶共振频率激励下观察到了谐波饱和现象和锯齿波. 关键词： 失谐驻波管 大振幅驻波 畸变 饱和     

CoSi2/Si (111) Interface study by X-ray standing waves

Summary The CoSi₂/Si (111) interface has been studied with the X-ray standing-wave technique. The interface (a 49? thick CoSi₂ layer) has been epitaxially grown on Si (111) under ultrahigh vacuum andin situ characterized with Auger spectroscopy and low-energy electron diffraction. The perpendicular lattice mismatch between epilayer and substrate has been measured with double-crystal X-ray diffraction. The X-ray standing-wave analysis gives clear indication that the Co atoms are fivefold coordinated at the interface. This work has been partially supported by Progetto Finalizzato ?Materiali e dispositivi per l'Elettronica a Stato Solido?.     

Mammalian spontaneous otoacoustic emissions are amplitude-stabilized cochlear standing waves

Mammalian spontaneous otoacoustic emissions (SOAEs) have been suggested to arise by three different mechanisms. The local-oscillator model, dating back to the work of Thomas Gold, supposes that SOAEs arise through the local, autonomous oscillation of some cellular constituent of the organ of Corti (e.g., the "active process" underlying the cochlear amplifier). Two other models, by contrast, both suppose that SOAEs are a global collective phenomenon--cochlear standing waves created by multiple internal reflection--but differ on the nature of the proposed power source: Whereas the "passive" standing-wave model supposes that SOAEs are biological noise, passively amplified by cochlear standing-wave resonances acting as narrow-band nonlinear filters, the "active" standing-wave model supposes that standing-wave amplitudes are actively maintained by coherent wave amplification within the cochlea. Quantitative tests of key predictions that distinguish the local-oscillator and global standing-wave models are presented and shown to support the global standing-wave model. In addition to predicting the existence of multiple emissions with a characteristic minimum frequency spacing, the global standing-wave model accurately predicts the mean value of this spacing, its standard deviation, and its power-law dependence on SOAE frequency. Furthermore, the global standing-wave model accounts for the magnitude, sign, and frequency dependence of changes in SOAE frequency that result from modulations in middle-ear stiffness. Although some of these SOAE characteristics may be replicable through artful ad hoc adjustment of local-oscillator models, they all arise quite naturally in the standing-wave framework. Finally, the statistics of SOAE time waveforms demonstrate that SOAEs are coherent, amplitude-stabilized signals, as predicted by the active standing-wave model. Taken together, the results imply that SOAEs are amplitude-stabilized standing waves produced by the cochlea acting as a biological, hydromechanical analog of a laser oscillator. Contrary to recent claims, spontaneous emission of sound from the ear does not require the autonomous mechanical oscillation of its cellular constituents.     

Long-range perturbations produced by a localized packet of ion-acoustic waves in a collisionless plasma

We demonstrate the in situ detection of cold ⁸⁷Rb atoms near a dielectric surface using the absorption of a weak, resonant evanescent wave. We have used this technique in time of flight experiments determining the density of atoms falling on the surface. A quantitative understanding of the measured curve was obtained using a detailed calculation of the evanescent intensity distribution. We have also used it to detect atoms trapped near the surface in a standing-wave optical dipole potential. This trap was loaded by inelastic bouncing on a strong, repulsive evanescent potential. We estimate that we trap 1.5×10⁴ atoms at a density 100 times higher than the falling atoms. Received 14 May 2002 Published online 8 October 2002 RID="a" ID="a"e-mail: spreeuw@science.uva.nl     

Trapping and storage of atoms in a laser field

Analysis of the possibility of spatial trapping of cold atoms in a standing-wave laser field is presented. It is shown that cold atoms can be trapped for a long time in region ≈ λ in a nonresonant standing-wave field. In a resonant standing-wave field cold atoms can be stored for a long time in the region determined by the cross-section of the laser beam. Trapping and storage together with cooling of atoms that has been suggested earlier allow us in specific cases to increase the sensitivity and the resolution of spectroscopic studies.     

Experimental study on the standing-wave tube with tapered section and its extremely nonlinear standing-wave field

A standing-wave tube with tapered section(STTS) was evolved from a standing-wave tube with abrupt section(STAS) whose abrupt section was replaced with tapered section. The research was intended to compare the acoustic properties and the extremely nonlinear pure standing waves of STTS with those of STAS.The acoustic properties of the STTS were studied with transfer matrix.It was proved,like the STAS,that the STTS was dissonant standing-wave tube.With its dissonant property,the 181 dB extremely nonlinear pure standing wave was obtained in the STTS excited at its first resonance frequency.Then the comparative experimental studies on the saturation properties of the extremely nonlinear standing waves were carried out in the STTS and the STAS with the same length.It was found that the STTS could suppress the harmonics and meanwhile reduce energy loss of the standing wave more effectively.Compared with the STAS,under the same voltage of loudspeaker,the STTS obtained a higher extremely nonlinear pure standing wave.Moreover,it was found for the STTS that the third harmonic of the third resonance frequency was close to the seventh resonance frequency of sound source impedance,to which the valley value of the sound pressure level transfer function corresponded.Because of this,the third harmonic increased rapidly with the increase of fundamental wave and tended to saturate.     

Two-dimensional atom localization via Raman-driven coherence

A scheme for two-dimensional (2D) atom localization via Raman-driven coherence in a four-level diamond-configuration system is suggested. The atom interacts with two orthogonal standing-wave fields where each standing-wave field is constructed from the superposition of the two-standing wave fields along the corresponding directions. Due to the position-dependent atom–field interaction, the frequency of the spontaneously emitted photon carries the position information about the atom. We investigate the effect of the detunings and phase shifts associated with standing-wave fields. Unique position information of the single atom is obtained by properly adjusting the system parameters. This is an extension of our previous proposal for one-dimensional atom localization via Raman-driven coherence [1].     

SQUEEZING PROPERTIES OF A TRAPPED ION IN THE STANDING-WAVE LASER

We investigate the squeezing properties of a trapped ion in a standing-wave laser. Our results show that the squeezing of a trapped ion in the standing-wave laser is dependent on its position in the latter, the detuning parameter and the initial average phonon number.     

Backscattering X-ray standing waves in the XUV region

It is demonstrated that Bragg reflection of XUV radiation can be used to study structural properties of crystalline materials with large unit cells. A standing-wave field is formed in a layered TiSe2 single crystal for a near-backscattering geometry (theta = 88.5 degrees). The partial electron yield is measured as a function of photon energy across the (001) Bragg reflection condition (hv approximately equal to 1033 eV) and its characteristic modulation is compared with the results derived from dynamical diffraction theory in the two-wave approximation. The data reveal a large amount of disorder along the c-axis.     

Optical responses of magnetic-vortex resonance in double-disk metamaterial variations

Optical toroidal resonance in structural variations of the double-disk metamaterial, in viewpoint of an equivalent LC-circuit model, is numerically studied to optimize its geometrically-dependent optical characteristics, such as the enhancement capability of local-field confinement and the extinction coefficient. Responses of high-order magnetic vortex resonances (i.e., the double- and triple-fold vortex modes), in addition to the fundamental toroidal dipole, are excited in accordance with a standing-wave model of oscillating current. The induced strengths for these vortex responses are sensitive, in different manners, to the incident angle of the light, though their frequencies are angularly independent.     

热声发动机的CFD数值模拟

采用计算流体动力学(CFD)方法,对高频驻波热声发动机和热声斯特林发动机实验系统分别进行了二维和三维数值模拟。计算模型具有与实验系统相同的几何结构、尺寸和运行工况。对计算模型的有效性进行了研究,表明实现有限换热条件的板叠实物模型适合驻波热声发动机的模拟,而实现局域热平衡的多孔介质模型适合热声斯特林发动机的模拟。计算结果成功观测到了非线性的自激振荡演化过程,捕捉到了两种发动机的不同非线性现象。计算结果分别给出了两种热声发动机内部的声场分布特性和复杂流场。计算结果与实验结果的对比验证了CFD方法对高频驻波热声发动机和热声斯特林发动机模拟的有效性。     

Snell's law for surface electrons: refraction of an electron gas imaged in real space

On NaCl(100)/Cu(111) an interface state band is observed that descends from the surface-state band of the clean copper surface. This band exhibits a Moiré-pattern-induced one-dimensional band gap, which is accompanied by strong standing-wave patterns, as revealed in low-temperature scanning tunneling microscopy images. At NaCl island step edges, one can directly see the refraction of these standing waves, which obey Snell's refraction law.