Responses of simple optical standing wave sensors

Optical standing wave sensors have been manufactured by amorphous silicon deposition. The responses of these sensors, when subjected to standing waves, have been calculated and measured. It is shown that the responses are different depending on the way the standing wave is created. The responses also depend on the thickness and material properties of the layers used to create the sensors. Quantitative agreement between measurements and model calculations can be obtained by including alignment errors, incoherent light interaction and scaling factors. The simple construction of the sensors allows for a broad application range.     

Liquid waveguide-based evanescent wave sensor that uses two light sources with different wavelengths

We demonstrate a prototypic optofluidic evanescent wave sensor made of poly(dimethylsiloxane) (PDMS) elastomer in which two light sources with different wavelengths are coupled into an optofluidic liquid-core/liquid-cladding (L(2)) waveguide. The exponentially decaying evanescent wave interacts with analyte molecules dissolved in the cladding fluids or products formed by in situ reactions at the core-cladding interface. The analyte molecules exhibit distinctly different light absorbance at the two wavelengths during the light-analyte interaction. Therefore, by using the normalized absorbance calculated from the intensity ratio of the two wavelengths instead of the absolute magnitude of either signal, unwanted effects from omnipresent external noise sources can be reduced. In addition, the differential absorption of the two beams by the analyte solutions can be used to enhance the resolution of sample analysis. The evanescent wave sensor based on a liquid waveguide can also be used for real-time monitoring of chemical reactions, because the core and cladding fluids in the L(2) waveguide are slightly miscible at the core-cladding interface due to the diffusional mixing.     

Relation between optical Fresnel transformation and quantum tomography in two-mode entangled case

In many applications of phase-shifting interferometry (PSI) the actually recorded object wave is the diffraction field of an object surface. In this case not only the phase error but also the amplitude error in the retrieval process have effects on the object wave reconstruction in its original plane. In this paper, for the first time that we know, the amplitude errors in wave reconstruction in PSI are discussed systematically. Some general relations between the amplitude errors and the phase errors for three commonly encountered error sources, namely the phase shift error, the light source intensity fluctuation and the detector nonlinearity, are revealed. The analytical expressions of the amplitude and phase errors for six frequently used algorithms in PSI are derived. The statistical variances of the two kinds of error are introduced to describe the overall performance of these algorithms and are quantitatively calculated. A series of computer simulations are also given as a verification of our analyses. These results can be used for evaluating the complete wave errors in PSI and developing new methods for their correction.     

Arrays and cascades of fluorescent liquid-liquid waveguides: broadband light sources for spectroscopy in microchannels

This paper describes the fabrication and operation of fluidic broadband light sources for use "on-chip" in integrated microanalytical systems. These light sources consist of liquid-core, liquid-cladding (L2) microchannel waveguides with liquid cores containing fluorescent dyes, excited by incident light from an external halogen bulb. Simultaneous use of multiple fluorophores in a common solution, in a single L2 light source, is not possible, because energy transfer from fluorophores emitting at shorter wavelength to fluorophores emitting at longer wavelength is essentially complete. Two approaches circumvent this problem of energy transfer; both use spatial separation of the fluorophores in different streams. The first setup uses a cascade (series) of single-core, single-dye light sources of increasing absorption energy to generate a combined broadband output. The second approach uses a parallel array of single-core, single-dye light sources. The spectral content of the light output for both cascade and array light sources can be controlled through choice of flow rates and dyes. Output intensity from these light sources is comparable to standard fiber-optic spectrophotometer light sources. The paper also discusses the efficiency of energy transfer between parallel liquid cores as a function of the fluid medium (index of refraction, path length, and rate of flow).     

A spectral finite element for axial-flexural-shear coupled wave propagation analysis in lengthwise graded beam

A new spectral element (SE) is formulated to analyse wave propagation in anisotropic inhomogeneous beam. The inhomogeneity is considered in the longitudinal direction. Due to this particular pattern of inhomogeneity, the governing partial differential equations (PDEs) have variable coefficients and an exact solution for arbitrary variation of material properties, even in frequency domain, is not possible to obtain. However, it is shown in this work that for exponential variation of material properties, the equations can be solved exactly in frequency domain, when the same parameter governs the variation of elastic moduli and density. The SE is formed using this exact solution as interpolating polynomial. As a result a single element can replace hundreds of finite elements (FEs), which are essential for all wave propagation analysis and also for accurate representation of the inhomogeneity. The developed element is used for eliciting several advantages of the gradation, including mode selection, mode blockage and smoothening of stress waves.     

A hybrid element method for steady linearized free-surface flows

It is first shown that the two-dimensional linearized ship wave problem can be recast as the sum of a radiation and a diffraction problem for simple harmonic waves. Each problem can be solved by a hybrid element method (HEM) where conventional finite elements are used near the body and analytical solutions are used in the remaining infinite regions (super-elements). Variational principles which incorporate the matching conditions between regular and super-elements as natural conditions are derived. Numerical examples are presented. The theoretical aspects for extending the above ideas to a three-dimensional ship wave problems are also described.     

Applicability of light-emitting diodes as light sources for active differential optical absorption spectroscopy measurements

We present what is to our knowledge the first use of light-emitting diodes (LEDs) as light sources for long-path differential optical absorption spectroscopy (LP-DOAS) measurements of trace gases in the open atmosphere. Modern LEDs represent a potentially advantageous alternative to thermal light sources, in particular to xenon arc lamps, which are the most common active DOAS light sources. The radiative properties of a variety of LEDs were characterized, and parameters such as spectral shape, spectral range, spectral stability, and ways in which they can be influenced by environmental factors were analyzed. The spectra of several LEDs were found to contain Fabry-Perot etalon-induced spectral structures that interfered with the DOAS evaluation, in particular when a constant temperature was not maintained. It was shown that LEDs can be used successfully as light sources in active DOAS experiments that measure NO2 and NO3 near 450 and 630 nm, respectively. Average detection limits of 0.3 parts in 10(9) and 16 parts in 10(12) respectively, were obtained by use of a 6 km light path in the open atmosphere.     

Multi-mode cylindrical surface wave excitation

In this paper, we study the solution of the 3-dimensional reduced wave equation above an infinite plane 2-dimensional surface wave supporting structure. The structure is simulated by a multiple impedance boundary condition that allows for the excitation of two different cylindrical surface wave modes. At first we investigate the problem of a simple source which is then generalized to multi-pole sources. For the cases considered, we are able to give an explicit solution that exhibits the character of the surface wave field. Furthermore, using a virtual structure notion, we are able to identify the power travelling within the impedance structure associated with a given external surface wave mode. Thus, a definition of the total surface wave power is applied in a manner that modal power flow separability is maintained. The far field pattern is observed to vanish in certain directions, in particular along the impedance plane. Furthermore, the far field power is calculated in terms of a non-elementary definite integral which is then estimated at high and low frequencies so that a partial verification of our calculations can be made by observing that power is conserved to these orders.     

两种光源光通量测量方法的比较

介绍两种光源光通量测量方法：加V（λ）修正的光度计法和分光法,比较各自的特点,并分析影响光通量测量结果的因素。加V（λ）修正的光度计法测量光通量简捷、快速,但无法同时测量光色参数。随着新型光电测试技术的日益成熟,光谱辐射计性能越发完善,除了测量光源光通量,还可计算光源的色品坐标、色温、显色指数、色容差等色度参数。在CIE127中分光法被推荐为测量光源光色参数的方法。     

Pulsed eddy-current response to a conducting half-space

Eddy-current nondestructive evaluation commonly carried out using single frequency time harmonic excitations, but a pulsed excitation offers a simple and effective alternative. The pulse signals have been calculated for a probe coil whose current rises and falls exponentially, approximating a square wave when the exponential time constant is small. Predictions of the induced electromotive force (EMF) across a coil above a half-space conductor and of the magnetic field on the coil axis have been compared with experiments. The comparison shows excellent agreement between theory and experiment     

Measuring the focal length of optical systems by grating shearing interferometry

Using grating shearing interferometry, a new and simple technique to measure the effective focal length of optical systems is described. The diffraction pattern of a phase grating positioned at the focal point of the lens under test is evaluated for this purpose. The relative lateral shift between the undiffracted zero order and the diffracted first orders caused by the grating is measured. By utilizing knowledge of the wavelength of light, the grating period, and the diameter of an aperture stop placed in front of the test lens, we can determine the effective focal length of the test lens. Results of measurements are presented and compared with calculated values. The dependence of the focal length on the wavelength of the light is shown by using two laser sources of different wavelengths. An analysis of the measurement accuracy is given.     

Call for Papers

Abstract

An expression is found for the propagation of the radiance function for light in any state of coherence through a concentrator which can be represented by a linear, stationary optical system. For light from a quasi-homogeneous source this expression can be somewhat simplified by an approximation. It is shown that the radiance function is invariant for a large class of optical systems. Finally it is shown that fundamental limitations for the concentration of light follow from the uncertainty principle and the second law of thermodynamics, which apply quite generally. These relations show why quasi-homogeneous light (i.e. light from thermal sources) cannot be concentrated as well as light from some other sources (such as light from a laser).     

Noise,anti-noise and fluid flow control

This paper celebrates Thomas Young's discovery that wave interference was responsible for much that is known about light and colour. A substantial programme of work has been aimed at controlling the noise of aerodynamic flows. Much of that field can be explained in terms of interference and it is argued in this paper that the theoretical techniques for analysing noise can also be seen to rest on interference effects. Interference can change the character of wave fields to produce, out of well-ordered fields, wave systems quite different from the interfering wave elements. Lighthill's acoustic analogy is described as an example of this effect, an example in which the exact model of turbulence-generated noise is seen to consist of elementary interfering sound waves; waves that are sometimes heard in advance of their sources. The paper goes on to describe an emerging field of technology where sound is suppressed by superimposing on it a destructively interfering secondary sound; one designed and manufactured specifically for interference. That sound is known as anti-sound, or anti-noise when the sound is chaotic enough. Examples are then referred to where the noisy effect to be controlled is actually a disturbance of a linearly unstable system; a disturbance that is destroyed by destructive interference with a deliberately constructed antidote. The practical benefits of this kind of instability control are much greater and can even change the whole character of flows. It is argued that completely unnatural unstable conditions can be held with active controllers generating destructively interfering elements. Examples are given in which gravitational instability of stratified fluids can be prevented. The Kelvin-Helmholtz instability of shear flows can also be avoided by simple controls. Those are speculative examples of what might be possible in future developments of an interference effect, which has made anti-noise a useful technology.     

Potentiometric response characteristics of polycation-sensitive membrane electrodes toward poly(amidoamine) and poly(propylenimine) dendrimers

The potentiometric response characteristics of polycation-sensitive membrane electrodes toward two classes of polycationic dendrimers are examined. Using appropriately formulated polymer membrane electrodes composed of a dinonylnaphthalenesulfonate (DNNS) salt in a plasticized polyurethane matrix, it is shown that poly(amidoamine) (PAMAM) and poly(propylenimine) (PPI) dendrimers are readily detected at submicrogram per milliliter levels via a nonequilibrium response mechanism. The relationship between the total EMF response (at equilibrium) and the specific dendrimer structure is also examined. For both the PAMAM and PPI species, it is shown that the total EMF response does not change significantly with dendrimer generation number; however, the nonequilibrium analytically useful response curves are shifted to higher mass concentrations as the generation number is increased. The relative contributions of the terminal primary amines and the interior tertiary amines of the dendrimers to the observed EMF response are investigated by synthesis of various dendrimer derivatives (acetylated, quaternized, etc.). By comparing the total EMF responses for these derivatives as a function of sample pH, it is demonstrated that the lipophilic cation exchanger (DNNS) within the membrane phase can likely interact electrostatically with both protonated forms of the terminal primary amines and interior tertiary amines of the dendrimer structures. The practical application of the nonequilibrium potentiometric detection of dendrimers for monitoring their interaction with DNA is also demonstrated.     

Reproduction in free space of fields confined by 3-dimensional optical waveguides

Abstract

It is shown by using the Fresnel-Kirchhoff diffraction theory and the method of images that a scalar field confined by a 3-dimensional optical waveguide can be generated in free space by a suitable light source. In the method the boundaries of a waveguide are replaced by virtual sources. This allows one to present the wave guiding as the interference and diffraction of multiple light beams produced in free space by the guide equivalent source (Fresnel waveguide). Thus, the scalar optics of a 3-dimensional waveguide is presented as the free-space beam optics. The method is illustrated by construction of the Fresnel sources for the triangular, rectangular and hexagonal waveguides. The numerical examples demonstrate the diffraction-free and self-imaging propagation in the free-space of the eigenmodes of the Fresnel rectangular-waveguide.     

Attenuation of an electromagnetic wave by charged dust particles in a sandstorm

We calculate the light scattering properties of the partially charged dust particles with the Mie theory for electromagnetic waves with different frequencies, and the attenuation coefficients of an electromagnetic wave propagating in a sandstorm are also calculated. The results show that the electric charges distributed on the sand surface have a significant effect on the attenuation of the electromagnetic wave, especially for a frequency lower than 40 GHz, and attenuation coefficients increase with the magnitude of charges carried by the dust particles (expressed by the charge-to-mass ratio in this paper). For the higher frequency electromagnetic wave, such as visible light, the effect of charges carried by sand particles on its attenuation is very little, which can be ignored.     

Influence of geometry on polychromatic speckle contrast

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.     

Dynamics of brittle fracture

The equation of motion and the stability conditions of surface cracks which are subjected to stress waves are derived from an energy balance and the law of angular momentum conservation. From the resulting differential equation the terminal crack velocity and dynamic threshold conditions can be derived. It will be shown that not only a critical stress (amplitude of the wave) but also a critical time (duration of the wave) are necessary to move the crack. These two critical quantities can be combined to a critical action. The specific action of the wave must exceed a certain minimal value for crack propagation to occur. Quantum considerations allow us to generalize this criterion further. Some simple applications of the least action law are mentioned. Supercritical stress pulses are also treated briefly. This leads to the concept of the cross section of a stress wave. Crack stability can also be treated as an eigenvalue problem.     

Analysis of quantum noise in a singly resonant nondegenerate optical parametric oscillator

We have analyzed the evolution of quantum operators in a three-wave mixing process by using the nonlinear polarization driven wave equations and linearization of the quantum operators. We have theoretically shown that a nondegenerate optical parametric amplifier can generate amplitude-squeezed light when operated in the backconversion regime. Furthermore, a nondegenerate optical parametric oscillator, where only the signal wave is resonant, is proved to generate amplitude-squeezed light when the pump intensity is above the value at which 100% photon conversion efficiency is achieved. The calculated limit for amplitude-squeezing in this case is 3 d B.     

The Spin Wave Gap and Switching Field in Thin Films with In-Plane Anisotropy

In this paper, we have calculated the spin wave gap and the angular dependence of magnetization reversal in a single-layer thin magnetic film that includes the strong perpendicular magnetic anisotropy and in-plane anisotropy. The film is assumed to be under the influence of the out-of-plane direction of the applied magnetic field at zero temperature. Using the quantum model, it is shown that the calculated equations present a nonzero spin wave gap at zero magnetic field which is strongly affected by anisotropies. The effects of the in-plane anisotropy and the role of the applied field were examined. We also discussed a simple theoretical model for the angular variation of switching field by using a quasi-classical argument. We used some constants in connection with experimental data which are reported for chromium telluride thin films grown by molecular beam epitaxy.