Photon detection with polarization discrimination

A simple and general method of using a photon detector to directly distinguish between two or three different polarizations is described. The method is suitable for a pre-selected limited wavelength region, for example as with encoded fibre optic communication. Alternatively, wavelength discrimination via wavelength selective polarization is possible.     

Experimental revealing of polarization waves

Stationary and traveling waves of the states of optical polarization are considered in the framework of Jones vector formalism. The feasibility of revealing these waves in holographic and interference arrangements is substantiated and demonstrated.     

Backscattering target detection in a turbid medium by polarization discrimination

We describe a method for increasing target contrast within a turbid medium by means of the polarization state of the scattered light. The backscattered Mueller matrices for various concentrations of 0.1-mum spherical scatterers were measured with and without a painted metal target. Simple discrimination based on detecting cross-polarized intensities is shown to be more effective than the use of total intensity information. As a result, the choice of polarization state is dictated primarily by the requirement to maximize depolarization at the target. This in general means that circularly polarized light is the optimum choice.     

Experimental demonstration of a defect-tolerant nanocrossbar demultiplexer

Ultradense memory and logic circuits fabricated at local densities exceeding 100 × 10(9) cross-points per cm(2) have recently been demonstrated with nanowire crossbar arrays. Practical implementation of such nanocrossbar circuitry, however, requires effective demultiplexing to solve the problem of electrically addressing individual nanowires within an array. Importantly, such a demultiplexer (demux) must also be tolerant of the potentially high defect rates inherent to nanoscale circuit fabrication. We have built a 50?nm half-pitch nanocrossbar circuit using imprint lithography and configured it for a demux application. Utilizing a class of Hamming codes in the hardware design, we experimentally demonstrate defect-tolerant demux operations on a 12 × 8 nanocrossbar array with up to two stuck-open defects per addressed line.     

Experimental demonstration of a single-molecule electric motor

For molecules to be used as components in molecular machines, methods that couple individual molecules to external energy sources and that selectively excite motion in a given direction are required. Significant progress has been made in the construction of molecular motors powered by light and by chemical reactions, but electrically driven motors have not yet been built, despite several theoretical proposals for such motors. Here we report that a butyl methyl sulphide molecule adsorbed on a copper surface can be operated as a single-molecule electric motor. Electrons from a scanning tunnelling microscope are used to drive the directional motion of the molecule in a two-terminal setup. Moreover, the temperature and electron flux can be adjusted to allow each rotational event to be monitored at the molecular scale in real time. The direction and rate of the rotation are related to the chiralities of both the molecule and the tip of the microscope (which serves as the electrode), illustrating the importance of the symmetry of the metal contacts in atomic-scale electrical devices.     

热声制冷效应验证的实验设计

热声制冷技术是一项新的冷制技术。它具有无运动部件、运行可靠、寿命长和环保等优点。在航天、微电子、低温物理及军事等领域有着十分诱人的应用前景。热声制冷机主要由声驱动器、共振管、热声叠和换热器等部件组成。根据热声制冷原理,利用常见的材料和仪器,采用自制的玻璃管状热声叠,设计了一套结构简单的扬声器驱动热声制冷实验验证装置。实验结果表明:以空气作工质,在无冷却措施的情况下,在系统运行较短时间内,实现了13℃的降温及25℃的温跨,热声制冷效应十分明显。该装置可用于研究热声制冷效应的影响因素。     

Experimental demonstration of a two-phase population extinction hazard

Population extinction is a fundamental biological process with applications to ecology, epidemiology, immunology, conservation biology and genetics. Although a monotonic relationship between initial population size and mean extinction time is predicted by virtually all theoretical models, attempts at empirical demonstration have been equivocal. We suggest that this anomaly is best explained with reference to the transient properties of ensembles of populations. Specifically, we submit that under experimental conditions, many populations escape their initially vulnerable state to reach quasi-stationarity, where effects of initial conditions are erased. Thus, extinction of populations initialized far from quasi-stationarity may be exposed to a two-phase extinction hazard. An empirical prediction of this theory is that the fit Cox proportional hazards regression model for the observed survival time distribution of a group of populations will be shown to violate the proportional hazards assumption early in the experiment, but not at later times. We report results of two experiments with the cladoceran zooplankton Daphnia magna designed to exhibit this phenomenon. In one experiment, habitat size was also varied. Statistical analysis showed that in one of these experiments a transformation occurred so that very early in the experiment there existed a transient phase during which the extinction hazard was primarily owing to the initial population size, and that this was gradually replaced by a more stable quasi-stationary phase. In the second experiment, only habitat size unambiguously displayed an effect. Analysis of data pooled from both experiments suggests that the overall extinction time distribution in this system results from the mixture of extinctions during the initial rapid phase, during which the effects of initial population size can be considerable, and a longer quasi-stationary phase, during which only habitat size has an effect. These are the first results, to our knowledge, of a two-phase population extinction process.     

Experimental demonstration of a continuously variant fractional fourier transformer

We demonstrate that an off-axis illuminated hemispherical-rod microlens acts as a fractional Fourier transformer with a continuously varying degree of fractionality. A complete theoretical treatment of the device as well as experimental results are presented.     

Retrieval of chlorophyll fluorescence from reflectance spectra through polarization discrimination: modeling and experiments

The polarization discrimination technique we recently developed, shows that it is possible to separate the elastic scattering and the chlorophyll fluorescence signal from the water-leaving radiance by making use of the fact that the elastically scattered components are partially polarized, while the fluorescence signal is unpolarized. The technique has been shown to be applicable to a wide range of water conditions. We present an extension of experimental and analytical results, which serve to define the scope of this technique and its range of applicability. A new analysis, based on vector radiative transfer computations, and on laboratory and field measurements on eastern Long Island and in the Chesapeake Bay, shows that the technique is generally effective for both open ocean and coastal waters, but that it is limited if the ocean bottom albedo and/or multiple scattering due to very high mineral particle concentrations result in depolarizing the water-leaving radiance. In addition, we show that in contrast with the polarization-based retrieval, the traditional method of extracting fluorescence height using the baseline method can give significant errors, particularly for coastal waters where it strongly overestimates the fluorescence values.     

Experimental investigation of linear polarization in high-birefringence single-mode fibers

We report on measurements of linear polarization ratio in high-birefringence fibers as a function of wavelength. Comparison with standard step-index and with dispersion-shifted fibers reconfirms that the modes of polarization-maintaining fibers are not linearly polarized.     

White-light interferometry with polarization phase-shifter at the input of the interferometer

Abstract

In white-light interferometry the surface profile is determined by measuring the fringe contrast function of the white-light interferogram. One of the techniques proposed for the measurement of the fringe contrast function is the use of the phase shifting technique with the help of an achromatic phaseshifter. The available phase-shifters employ a rotating polarization component at the output end of the interferometer. Using a rotating polarization component at the input end, rather than at the output end, has certain advantages. In this paper we investigate a rotating half-wave plate phase-shifter at the input end for its applications to a white-light interferometer.     

Experimental demonstration of the spectral interference between two linearly polarized modes at the output of a fibre waveguide excited by a low-coherence source

Abstract

The mutual interference of two linearly polarized (LP) modes in the frequency domain has been demonstrated experimentally at the output of a fibre waveguide excited by a low-coherence source when the optical path difference between both LP modes exceeds the coherence length of the source. The spectral interference between two LP modes, which shows up a periodic modulation of the source spectrum, serves as an illustration of the experimental verification of conclusions we have made in previous theoretical works. Consequently, the feasibility of a novel experimental method utilizing a high-resolution spectrometer in the evaluation of the group-delay time difference between both LP modes has been confirmed.     

Experimental demonstration of an automatic alignment system for optical interferometers

An automatic alignment system, based on a differential phase-sensing technique described in a companion paper [Appl. Opt.33, 0000, (1994)], has been experimentally demonstrated on the 10-m prototype laser interferometric gravitational wave detector in Glasgow. The alignment system developed was used to control the orientations of two mirrors in a 10-m-long suspended Fabry-Perot cavity with respect to the direction defined by the input laser beam. The results of the test and a discussion of the performance of the system are given.     

Experimental demonstration of resonant sideband extraction in a sagnac interferometer

Sagnac interferometers have recently been proposed as a potential alternative to Michelson interferometers for the purpose of large-scale laser interferometric gravitational-wave detectors. We report on an experimental investigation of the Sagnac interferometer in two configurations: with arm cavities, and with resonant sideband extraction. Resonant sideband extraction was shown to increase the signal bandwidth by a factor of 6.5 compared with the arm cavity device, corresponding to an increase in sensitivity of as much as 6 dB for signals outside the arm cavity bandwidth. Moreover, we compare the performance of a Sagnac interferometer with resonant sideband extraction to a Michelson interferometer with resonant sideband extraction.     

Experimental demonstration of kinogram-based single-phase decryption technique for information security

The kinogram-based single-phase decryption technique is experimentally demonstrated. Only one phase spatial light modulator is used to simultaneously display the encrypted information and the decrypting key. The intensity decrypted image is obtained by Fourier transforming the phase decrypted information. We investigate the effect of the binary and multiphase keys on the security level of the encrypted information. The accepted displacement of the decrypting key within the system is determined. The influence of the optical system bandwidth and noise on the decryption quality is also investigated.     

A numerical demonstration of discontinuous directional motion at the nanometre scale

Classical molecular dynamics simulations have been employed to investigate the behaviour of a relatively complex assembly of carbon nanotubes embedded into a CF4 liquid phase submitted to heating and cooling cycles. The assembly is formed by two concentric capsule-like carbon nanotubes, the smaller of which located in the interior of the larger one, which has a partially open end. The carbon nanotubes have radii such that the distance between their cylindrical walls, though keeping attrition negligible, does not permit the passage of chemical species from one side of the inner capsule to the other. CH4 molecules in liquid phase are confined between the capped end of the outer nanotube and the inner capsule. On the other side, CF4 molecules can access the volume available between the inner capsule and the outer nanotube through its open end. When temperature is raised, the confined CH4 molecules undergo the liquid-gas transition. The consequent volume expansion pushes the inner capsule in the direction of the open end of the outer nanotube, which determines the rapid ejection of the CF4 molecules. This generates a thrust that allows the motion of the whole assembly in the direction opposite to ejection. When temperature is decreased and CH4 molecules return in the liquid phase, the system slowly recovers the initial configuration. The whole cycle of operation is fully reversible and allows the assembly to directionally move into the liquid phase.     

Experimental investigation of saturated polarization spectroscopy for quantitative concentration measurements

Polarization-spectroscopy (PS) line shapes and signal intensities are measured in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) pump beam intensities in the counterpropagating pump-probe geometry. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The PS signal intensities are used to measure relative OH number densities in a series of near-adiabatic flames at equivalence ratios (phi) ranging from 0.5 to 1.5. The use of saturating pump intensities minimizes the effect of pump beam absorption, providing more accurate number density measurements. When calibrated to the calculated OH concentration in the phi = 0.6 flame, the saturated PS number density measurements probing the P(1)(2) transition are in excellent agreement with OH absorption measurements, equilibrium calculations of OH number density, and previous saturated degenerate four-wave mixing OH number density measurements.     

A polarization theory for the scattering of sound at imperfect interfaces

In a recent article the author gave a general theory of scattering by thin layers included in a continuous matrix. Such layers may be thought of as plates, shells, coatings, or interface layers depending on the particular physical context. It was shown that, in the general case, the scattering may be described in terms of the stress and momentum polarizations in the layer and that when the latter is thin compared with the wavelength of the incident sound, the through-thickness average polarizations satisfy certain boundary integral equations. In this article we develop the theory in the context of imperfect interfaces such as those which may occur in adhesive and diffusion bonds. The advantage of this approach is that it can account for general inhomogeneities and interfacial roughness provided that the root mean square thickness is small compared with the wavelength.     

Reflection from bound microbubbles at high ultrasound frequencies

Targeted contrast agents and ultrasound imaging are now used in combination for the assessment and tracking of biomarkers in animal models in vivo. These applications have triggered interest in the understanding and prediction of the ultrasound echoes from contrast agents attached to cells. This study describes the reflection enhancement due to microbubbles bound on a gelatin surface. The reflection enhancement was measured using ultrasound pulses at high frequency (40 MHz) and low pressure (38 kPa peak-negative pressure) allowing a linear approximation to be applied. The observed reflection coefficient increased with the number of microbubbles, until reaching saturation at 0.9 when the surface coverage fraction was 35%. A multiple scattering model assuming that the targeted microbubbles are confined within an infinitesimally thin layer appeared suitable in predicting the reflection coefficient even at very high surface densities. These results could permit the optimization of the sensitivity of high frequency ultrasound to targeted contrast agents.     

Experimental demonstration of photonic bandgaps in azopolymer resonant waveguide grating systems

Photonic bandgaps are demonstrated in one-dimensional corrugated waveguides in the infrared range. A coupling grating is superimposed with single and double Bragg gratings on an azopolymer film by a simple optical process, which allows easy control of the grating spacing. Light is coupled to the TE(0) resonant mode, and gaps in the dispersion curve are introduced by careful selection of the gratings. The analysis is carried out by measuring the transmission through the waveguide as a function of the wavelength and angle of incidence of a probe beam. This results in a direct measurement of the dispersion curves, which are in excellent agreement with theory.