Optically guided beam splitter for propagating matter waves

We study experimentally and theoretically a beam splitter setup for guided atomic matter waves. The matter wave is a guided atom laser that can be tuned from quasimonomode to a regime where many transverse modes are populated, and propagates in a horizontal dipole beam until it crosses another horizontal beam at 45°. We show that depending on the parameters of this X configuration, the atoms can all end up in one of the two beams (the system behaves as a perfect guide switch), or be split between the four available channels (the system behaves as a beam splitter). The splitting regime results from a chaotic scattering dynamics. The existence of these different regimes turns out to be robust against small variations of the parameters of the system. From numerical studies, we also propose a scheme that provides a robust and controlled beam splitter in two channels only.     

Realization of a distributed Bragg reflector for propagating guided matter waves

We report on the experimental study of a Bragg reflector for guided, propagating Bose-Einstein condensates. A one-dimensional attractive optical lattice of finite length created by red-detuned laser beams selectively reflects some velocity components of the incident matter wave packet. We find quantitative agreement between the experimental data and one-dimensional numerical simulations and show that the Gaussian envelope of the optical lattice has a major influence on the properties of the reflector. In particular, it gives rise to multiple reflections of the wave packet between two symmetric locations where Bragg reflection occurs. Our results are a further step towards integrated atom-optics setups for quasi-cw matter waves.     

Observation of the first excited transverse mode in guided matter waves

In direct analogy to the textbook example of light guided in a few-mode fiber (FMF), we report the observation of the first excited mode of an optically guided atomic beam. We selectively excite the atomic analog of the LP?? optical mode by controlling the energy distribution of ultracold atoms loaded into the guide, resulting in a modal structure dominated by a 47(2)% population in the first excited transverse mode. The ability to guide lower-order modes has been essential to demonstrating optical effects such as multimode interferometry, slow light, and entanglement, and an atomic analog to a FMF may lead to similarly useful applications.     

Active interferometer as an antenna for gravitational waves

It is demonstrated that a gain medium in the cavity of the Michelson interferometer that serves as a detector of gravitational waves allows a sharp decrease in the output power of the external laser source.     

A Michelson interferometer using electron waves

An electron interferometer of the Michelson type is realized. Monoenergetic 25 keV electrons emitted from a line source 1000 Å in width are deflected by 90 ° in a magnetic Castaing prism and reflected on two mirrorsM ₁ andM ₂ held at a potential ΔU _m negative with respect to the cathode. In the experiment the mirrors are represented by height differences on the surface of an silvered glass plate. The reflected electrons are once more deflected by the magnetic prism behind which the coherent partial beams 1 and 2 reflected on the mirrorsM ₁ andM ₂, respectively, are superimposed using an electrostatic biprism to form two-beam interferences. The observed fringe shift indicates a phase shift due to differences in height between the equipotentials reflecting the partial beams 1 and 2. It is estimated that path differences less than the electron wavelength of 0.08 Å can be observed.     

Wave equations for matter force waves

Regarding phase space—time as a physical space for quantum matter particles, the wave equations are considered in the cases of scalar, vector, and spinor fields. Electrodynamics in pulsed space—time does not contain singularities in the force fields. Expressions are found for the particle propagators in momentum subspace. Order-of-magnitude estimates of force-wave emission and absorption for atomic and nuclear structures show that force waves cannot be neglected in nuclear processes. Force waves are not emitted by particles in a constant force field; the rate of emission is proportional to the square of the rate of force variation over time.NIIVTs Research Center, M. V. Lomosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 32–39, July, 1994.     

Dispersion management for atomic matter waves

We demonstrate the control of the dispersion of matter wave packets utilizing periodic potentials. This is analogous to the technique of dispersion management known in photon optics. Matter wave packets are realized by Bose-Einstein condensates of 87Rb in an optical dipole potential acting as a one-dimensional waveguide. A weak optical lattice is used to control the dispersion relation of the matter waves during the propagation of the wave packets. The dynamics are observed in position space and interpreted using the concept of effective mass. By switching from positive to negative effective mass, the dynamics can be reversed. The breakdown of the approximation of constant, as well as experimental signatures of an infinite effective mass are studied.     

Spectral and perturbation analysis for ultrasonic guided waves

The influence of damage on waves propagating in complex geometry waveguides is investigated through a numerical model formulated by combining the Spectral Finite Element Method and Perturbation Techniques. The resulting numerical tool allows efficient computation of the wave propagation response and the analysis of the effects of damages of various extent and location. The dynamic behavior of the damaged waveguides is described through a general higher order model which couples different waves thus allowing the prediction of mode conversion phenomena. Arbitrary cross-section can be considered through Finite Element (FE) discretization according to well-established Semi-Analytical Finite Element (SAFE) procedures. Two types of damages which allow the application of perturbation theory are considered: a small localized reduction of the thickness and a reduction of material stiffness and density. A validation by comparison with a Finite Element Model as well as numerical examples are presented to illustrate the model capabilities.     

超声导波管道缺陷定位方法研究

该文提出了一种基于多换能器的超声导波管道缺陷定位方法,利用两个环形换能器阵列分别接收与缺陷相关的反射信号和透射信号,实现管道缺陷轴向及周向定位。首先利用变分模态分解法对信号进行滤波,在滤除噪声的基础上对信号进行小波变换,获得缺陷反射的导波时频信息,根据反射波的渡越时间计算缺陷在管道轴向的位置。在缺陷的周向定位上,提出一种损伤指数迭代方法,根据透过缺陷后导波的损伤指数来计算缺陷的周向位置及周向长度。仿真和实验结果表明,该文所采用的方法能够较为准确地测量出管道上缺陷的位置及周向长度。     

Holography with guided optical waves

This paper deals with “waveguide holograms” recorded in a layer of storage material covering a planar dielectric waveguide. Reference and read-out waves are guided modes of the waveguide. Their field in the storage medium is evanescent. A theory of the diffraction efficiencies of these waveguide holograms is presented fors-polarized wavefields. To calculate the hologram structure the attenuation of the reference wave caused by absorption in the light-sensitive storage material is taken into account. Analytical expressions for the local and the overall diffraction efficiencies and for the intensity profiles of the diffracted fields are derived. The dependence of these quantities on experimental parameters (the waveguide thickness, the mode numbers of the reference and read-out waves, and the angle of incidence of the plane object wave) is presented graphically, i.e., by computer plots. Grating couplers for integrated optics can be made by waveguide holography. We consider this application to be interesting because incoupling efficiencies for Gaussian beams of up to 96% can be achieved theoretically.     

Holography with guided optical waves

Waveguide holograms are recorded in a storage material layer covering a planar dielectric waveguide with a guided mode as reference wave. They are also read-out with a guided mode. In the storage material, assumed to have a lower refractive index than the waveguiding film, the fields of the reference and of the read-out wave are evanescent waves. We describe the preparation of the epoxy resin (Araldit) waveguides on glass substrates, their coating with a dichromated gelatin (DCG) layer as storage material, the processing of the DCG, and the recording and reconstruction techniques. Waveguide holograms of good quality with a size of several square centimeters have been realized for the first time. The holograms were recorded and read-out with wavelength λ=488 nm. They have a length of about 25 mm and a width of 17 mm. To obtain holograms that wide a special prism coupler had to be used which allowed to couple in a laser beam of elliptical cross section, and thus to excite a guided reference or read-out mode with a width of 17 mm.     

High-order Talbot fringes for atomic matter waves

We observe the interference of de Broglie waves in the diffraction near field of a microfabricated grating. The reduction of the grating period by self-imaging of second to seventh order is spatially resolved. We investigate the dependence of this effect on the de Broglie wavelength by a time-to-flight technique.     

Strangeness of matter waves

The concept of waves associated with any material particle has been a considerable boost to theoretical physics, and it appears to be in accordance with many experimental results. Some relativistic properties of these assumed waves are studied in comparison to other physical waves. It turns out that matter waves may nor be considered as objectively real, and that any physics resting on such a concept can only be subjective.     

Cloaking of matter waves

Invariant transformation for quantum mechanical systems is proposed. A cloaking of matter wave can be realized at given energy by designing the potential and effective mass of the matter waves in the cloaking region. The general conditions required for such a cloaking are determined and confirmed by both the wave and particle (classical) approaches. We show that it may be possible to construct such a cloaking system for cold atoms using optical lattices.     

Power-mode theorems for guided acoustic waves in piezoelectric media

Relationships between complex power flow pseudo energy, propagation constant and complex frequency are presented for acoustic waves in piezoelectric media. These relationships are essentially energy-power equations which apply to anisotropic, nonconservative, dispersive, linear systems, analogous to those obtained by Chorney and Penfield for guided electromagnetic waves. At vanishing piezoelectric coupling the powermode theorems split into a proper electromagnetic set and a proper mechanical set. By differentiating the power-mode equations with respect to the complex frequency further results are obtained linking the group velocity with power flow and energy storage. Conclusions may be drawn from these expressions regarding the signature of the dispersion (forward or backward waves). The equipartition of pseudo energy is established at cut-off, and the vanishing of the complex power flow at resonance. Examples including wave propagation in lossless and lossy media are included.     

Chirp excitation of ultrasonic guided waves

Most ultrasonic guided wave methods require tone burst excitations to achieve some degree of mode purity while maintaining temporal resolution. In addition, it is often desirable to acquire data using multiple frequencies, particularly during method development when the best frequency for a specific application is not known. However, this process is inconvenient and time-consuming, particularly if extensive signal averaging at each excitation frequency is required to achieve a satisfactory signal-to-noise ratio. Both acquisition time and data storage requirements may be prohibitive if responses from many narrowband tone burst excitations are measured. Here chirp excitations are utilized to address the need to both test at multiple frequencies and achieve a high signal-to-noise ratio to minimize acquisition time. A broadband chirp is used to acquire data at a wide range of frequencies, and deconvolution is applied to extract multiple narrowband responses. After optimizing the frequency and duration of the desired tone burst excitation, a long-time narrowband chirp is used as the actual excitation, and the desired tone burst response is similarly extracted during post-processing. Results are shown that demonstrate the efficacy of both broadband and narrowband chirp excitations.     

Surface waves guided by magnetic metamaterials

We consider electromagnetic waves guided by slabs of anisotropic resonant magnetic metamaterials in free space and in metal waveguides. It is shown that wave propagation is possible in a waveguide below cutoff with an insert of such a metamaterial. The dependence of the dispersion properties of waves on the geometric sizes of the insert and the waveguide are studied. The obtained results can be used for miniaturization of electrodynamic systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 618–625, July 2006.     

Nonlinear waves guided by graded-index films

We derive both the dispersion relation and the power flow for waves guided by a linear graded-index film in contact with an arbitrary nonlinear cladding. For an exponential-like graded-index profile and a Kerr-like nonlinearity we present numerical results and compare them with those familar from the step-index profile.     

True surface waves guided by metamaterials

The dispersion properties of surface waves propagating along the interface between a resonant metamaterial and vacuum have been studied. It is shown that such an interface can support both forward and backward waves. The case of degeneracy, where an infinite number of waves with arbitrary retardation correspond to one frequency, has been investigated.