Contrast Of Interference Fringes Research Articles

Method for enhancing the contrast in a neutron interferometer using magnetic birefringence

We report a new method that uses magnetic birefringence to enhance the contrast in a neutron interferometer. We performed model calculations for interference-fringe contrast in a Mach-Zehnder-type neutron interferometer with an improperly aligned multilayer mirror and inhomogeneous magnetic fields. Our calculations showed that, by using inhomogeneous magnetic fields, we could recover the decreased contrast caused by the improper alignment of the mirrors.

Photon-counting digital holography under ultraweak illumination

Digital holography based on photon counting under ultraweak illumination was demonstrated. A hologram was recorded with two-dimensional scanning of an optical fiber connected to a single-photon counting detector under an illumination of 43 photons per second, and the object image was clearly reconstructed in a computer from the hologram. The dependence of hologram quality on the illumination light intensity was estimated from the contrast and phase deviation of interference fringes obtained by photon-counting measurements.

Design of a compact static Fourier transform spectrometer in integrated optics based on a leaky loop structure

A compact static Fourier transform spectrometer for integrated optics is proposed. It is based on a plane leaky loop structure combined with a plane waveguide. The interference pattern produced in the loop structure leaks outside of it and is guided in the plane waveguide to the photodetector array. This configuration allows one to control the shape of the field pattern at the end of the plane waveguide. A large fringe pattern with a high interference fringe contrast is obtained. A two-dimensional model based on an aperiodic Fourier modal method is used to modelize the coupling between the bent and the plane waveguides, completed with the Helmholtz-Kirchhoff propagation. This concept gives access to plan and compact spectrometers requiring only a single low-cost realization process step. The simulation has been done to realize a spectrometer in glass integrated optics (Deltalambda=6.1 nm at 1500 nm).

Numerical investigation of contrast degradation of Bose-Einstein-condensate interferometers

We use the mean-field approximation to numerically study the dynamics of a split condensate in Mach-Zehnder-type atom interferometers that employ Bragg diffraction. The Husimi representation is used as a direct tool for diagnosing the dynamics in phase space, thus providing information on the interference fringe contrast. We analyze how optimization of the contrast of interference signals can result by means of compensating for the nonlinear interaction and the trapping potential for three alternative experimental schemes. The phase-space overlap in Husimi distribution as well as dynamics in phase space is shown to be important in determining the interference fringe contrast.

Finite-temperature coherence of the ideal Bose gas in an optical lattice

In current experiments with cold quantum gases in periodic potentials, interference fringe contrast is typically the easiest signal in which to look for effects of nontrivial many-body dynamics. In order better to calibrate such measurements, we analyze the background effect of thermal decoherence as it occurs in the absence of dynamical interparticle interactions. We study the effect of optical lattice potentials, as experimentally applied, on the condensed fraction of a noninteracting Bose gas in local thermal equilibrium at finite temperatures. We show that the experimentally observed decrease of the condensate fraction in the presence of the lattice can be attributed, up to a threshold lattice height, purely to ideal-gas thermodynamics; conversely, we confirm that sharper decreases in first-order coherence observed in stronger lattices are indeed attributable to many-body physics. Our results also suggest that the fringe visibility ``kinks'' observed in Gerbier et al., Phys. Rev. Lett. 95, 050404 (2005) may be explained in terms of the competition between increasing lattice strength and increasing mean gas density, as the Gaussian profile of the red-detuned lattice lasers also increases the effective strength of the harmonic trap.

Probing quantum and thermal noise in an interacting many-body system

The probabilistic character of the measurement process is one of the most puzzling and fascinating aspects of quantum mechanics. In many-body systems quantum mechanical noise reveals non-local correlations of the underlying many-body states. Here, we provide a complete experimental analysis of the shot-to-shot variations of interference fringe contrast for pairs of independently created one-dimensional Bose condensates. Analyzing different system sizes we observe the crossover from thermal to quantum noise, reflected in a characteristic change in the distribution functions from Poissonian to Gumbel-type, in excellent agreement with theoretical predictions based on the Luttinger liquid formalism. We present the first experimental observation of quasi long-range order in one-dimensional atomic condensates, which is a hallmark of quantum fluctuations in one-dimensional systems. Furthermore, our experiments constitute the first analysis of the full distribution of quantum noise in an interacting many-body system.

Statistical analysis of a scatter plate interferometer

A scatter plate interferometer is analyzed based on the principle of statistical optics for what is to my knowledge the first time. It is shown that the optical complex amplitude distribution of scattered-direct light that is scattered by the first scatter plate and transmitted through the second scatter plate is equivalent to the distribution of direct-scattered light that is transmitted through the first scatter plate and scattered by the second scatter plate if there are no aberrations in the tested optical elements. Then the mechanism producing interference fringes and fringe contrast are discussed by means of a statistical method. It is shown that the fringe pattern depends on the correlation of the transmittance distributions of the two scatter plates and the aberration of the tested lens. The analysis coincides with experimental phenomena. The method used gives a new viewpoint on the principles of scatter plate interferometry and reveals its statistical nature.

The LCPDI: A Compact and Robust Phase-Shifting Point-Diffraction Interferometer Based on Dye-Doped LC Technology

Point-diffraction interferometers, by design, are much less sensitive to environmental disturbances than dual-path interferometers, but, until very recently, have not been capable of phase shifting. The liquid crystal point diffraction interferometer (LCPDI) utilizes a dye-doped, liquid crystal (LC), electro-optical device that functions as both the point-diffraction source and the phase-shifting element, yielding a phase-shifting diagnostic device that is significantly more compact and robust while also using fewer optical elements than conventional dual-path interferometers. These attributes make the LCPDI of special interest for diagnostic applications in the scientific, commercial, military, and industrial sectors, where vibration insensitivity, power requirements, size, weight, and cost are critical issues. Until very recently, LCPDI devices have used a plastic microsphere embedded in the LC fluid layer as the point-diffraction source. The process for fabricating microsphere-based LCPDI devices is low-yield, labor-intensive, very “hands-on,” and great care and skill are required to produce devices with adequate interference fringe contrast for diagnostic measurements. With the goal in mind of evolving the LCPDI beyond the level of a laboratory prototype, we have developed “second-generation” LCPDI devices in which the reference diffracting elements are an integral part of the substrates by depositing a suitable optical material (vapor-deposited thin films or photoresist) directly on the substrate surface. These “structured” substrates eliminate many of the assembly difficulties and performance limitations of previous LCPDI devices as well as open the possibility of mass-producing LCPDI devices at low cost by the same processes used to manufacture commercial LC displays.

Non-destructive testing with double-pulsed laser ESPI

Electronic Speckle Pattern Interferometry (ESPI) is an attractive method for non-destructive testing. There are two ESPI working modes: addition ESPI mode and subtraction ESPI mode. Overcoming the disadvantage of the subtraction ESPI mode, which strictly requires that there is no movement among the optical parts in an ESPI system, in the addition ESPI mode, the movement of a measured material is 'frozen' with a short-pulsed laser. As a result, the addition ESPI mode is believed to be feasible in adverse conditions where the subtraction ESPI mode is inapplicable. Based on the theory of double-pulsed laser ESPI, the interference fringe contrast and a simulation method are introduced in this paper. In the simulation, a compound material with a flaw is interrogated. Due to the fact that a result can only be obtained when the interference fringe passes through a special electronic filter, the filter applied to the experiment needs delicate fabrication. Its quality and central frequency influence the final interference fringe result. Therefore, a series of the filters are designed such as band-pass and high-pass filters, with a specific method applied. Subsequently, the result of the simulation for NDT with double-pulsed ESPI method is acquired and analysed.

Correlation and the density-matrix approach to inelastic electron holography in solid state plasmas

Collective excitations in solid state plasmas are a good candidate to measure correlation lengths of conduction electrons. The method of choice seems to be energy filtered electron holography in the transmission electron microscope (TEM) since the interference fringes contain information on the partial coherence of those electrons. Previous experiments showed surprisingly high coherence. We calculate the density-density correlation function in the Al plasma excitation from the dynamic form factor and compare it to results based on similar arguments. For the Al plasma excitation, we find a small extension of 0.1-0.3 nm over which the movement of charges is correlated. Using the density-matrix formalism, the coherence length of plasmon scattered fast electrons in the TEM is calculated and found to agree with experiment. We show that the small correlation length of conduction electrons does not contradict the coherence length of >10 nm found for fast probe electrons having excited a plasmon in Al. The difference of nearly two orders of magnitude can be traced back to the long-range Coulomb interaction between probe and target electrons. Two unexpected predictions ensue from the present approach: Inelastic holography experiments should show strongly increased contrast of interference fringes in vacuo, i.e., outside the specimen, andmore » contrast inversion of fringes in inelastic holograms of very small particles.« less

Non-Dispersive Measurement of the Transverse Coherence Length of a Cold Neutron Beam

We have measured the transverse coherence length of a cold neutron beam using Jamin-type cold neutron spin interferometer. It can control the transverse shift between the superposed two paths with no dispersion. We have observed clearly that the contrast of interference fringes varies according to the coherence function determined by the collimation of the beam. The measured coherence length was consistent with the estimate by the standard deviation of the neutron transverse momentum distribution.

Grating-assisted demodulation of interferometric optical sensors.

Accurate and dynamic control of the operating point of an interferometric optical sensor to produce the highest sensitivity is crucial in the demodulation of interferometric optical sensors to compensate for manufacturing errors and environmental perturbations. A grating-assisted operating-point tuning system has been designed that uses a diffraction grating and feedback control, functions as a tunable-bandpass optical filter, and can be used as an effective demodulation subsystem in sensor systems based on optical interferometers that use broadband light sources. This demodulation method has no signal-detection bandwidth limit, a high tuning speed, a large tunable range, increased interference fringe contrast, and the potential for absolute optical-path-difference measurement. The achieved 40-nm tuning range, which is limited by the available source spectrum width, 400-nm/s tuning speed, and a step resolution of 0.4 nm, is sufficient for most practical measurements. A significant improvement in signal-to-noise ratio in a fiber Fabry-Perot acoustic-wave sensor system proved that the expected fringe contrast and sensitivity increase.

Multiple successive two-beam interference of light on a semiconductor metallic layer

It is shown that it is possible in practice to carry out multiple successive two-beam interference of light on a semitransparent metallic layer. Semitransparent layers made from certain metals give interference fringes of equal slope that are virtually coincident in phase on the two images of the source in a two-beam interferometer. This makes it possible to again superimpose the output beams on such a layer. A semitransparent chromium layer and a Mach-Zehnder interferometer with additional superpositions of the beams were used for this work. Patterns of the superposition of several systems of contrast interference fringes and the results of photometry are presented. The possibility of creating wide-angle stages for a narrow-band optical filter is discussed as the first use of this form of interference.

ボールねじ軸の有効径自動測定装置の開発

A wave-optical simulator was coded and applied to the predictions of reflected beam qualities such as profiles of intensity and wavefront phase. Reflected beam qualities of flat mirrors with artificial bumps, which were modeled by Gaussian functions having a height of 1nm and widths from 0.06mm to 54mm, are investigated in the case of relatively short distance from the mirror center to the observing point such around 1m-long. As a result, bumps with the widths around 1mm make high contrast interference fringes in the reflected beam. Simulated results are examined and confirmed to be in good agreements.

Lossy purification and detection of entangled coherent states

In work by Howell and Yeazell [Phys. Rev. A 62, 012102 (2000)], a proposal is made to generate entangled macroscopically distinguishable states of two spatially separated traveling optical modes. After considering a preparation with nonperfect photodetection, we discuss a random mode of entanglement purification without manual intervention using a number of preparations transmitted over a lossy optical transmission line. An efficiency greater than 1/2 of the purification scheme is required to increase entanglement at all. Furthermore, we study a nondemolition configuration to measure the purity of the state as contrast of interference fringes in a double-slit setup. As a consequence of the relationship between purity and entanglement of formation resulting from treating the entangled coherent states as a state of a bipartite quantum system, the contrast of interference fringes provides a direct means to measure entanglement.

Effects of Fresnel Corrections for Phase-Shifting Electron Holography

Phase-shifting electron holography [1] is a useful technique for detecting a small phase change of an electron wave. In this method, however, Fresnel diffraction at an electron biprism causes two kinds of problems to the reconstructed phase. One is the influence on the amplitude of the electron wave, i.e. Fresnel fringes, resulting in non-uniform contrast of interference fringes. The non-uniform fringes bring numerical phase errors in reconstructed images. In order to remove the phase errors, we calculated the envelopes of the fringes, and normalized the non-uniform contrast. [2] The other problem is that Fresnel diffraction directly distorts the phase of the electron waves. We prepare the reference holograms that were taken in a vacuum without specimens, and then correct the distortion by subtracting the reconstructed phase of the reference holograms from that of holograms. [2] In this report, we evaluate the effects of the above correction methods (Fresnel corrections) using a computer simulation and show the possibility of observing a very small amount of electric charges.

Flatland optics. III. Achromatic diffraction.

In the previous two sections of "Flatland optics" [J. Opt. Soc. Am. A 17, 1755 (2000); 18, 1056 (2001)] we described the basic principles of two-dimensional (2D) optics and showed that a wavelength lambda in three-dimensional (3D) space (x, y, z) may appear in Flatland (x, z) as a wave with another wavelength Lambda=lambda/cos alpha. The tilt angle alpha can be modified by a 3D-Spaceland individual, who then is able to influence the 2D optics in a way that must appear to be magical to 2D-Flatland individuals-in the spirit of E. A. Abbott's science fiction story of 1884 [Flatland, a Romance of Many Dimensions, 6th ed. (Dover, New York, 1952)]. Here we show how the light from a white source can be perceived in Flatland as perfectly monochromatic, so diffraction with white light will be free of color blurring and the contrast of interference fringes can be 100%. The basic considerations for perfectly achromatic diffraction are presented, along with experimental illustration of Talbot self-imaging performed with broadband illumination.

Atomic Interference Method for Direct Measurement of the Wigner Function of a Cavity Field**The project supported by National Natural Science Foundation of China under Grant No. 60008003, Science Research Foundation of Education Office of Fujian Province of China under Grant No. K20004, and Funds from Fuzhou University

We propose a scheme for the reconstruction of a cavity field state. In the scheme the cavity field is first displaced by a microwave source, and then is placed in front of one slit of the two-slit apparatus. Ground state atoms pass through the apparatus, hitting upon the screen far away from the two-slit apparatus. The atom-field interaction is dispersive. The contrast of interference fringes is directly related to the Wigner function for the field state. The scheme can be easily generalized to measure the Wigner function of an entangled state of two spatially separated single-mode cavities.

An all guided three-arm interferometer for stellar interferometry

Following the first demonstration of an all guided two-beam stellar interferometer designed for space missions, we report an experiment recombining the beams coming from three telescopes using only guided optics components. This additional aperture could give us the possibility to achieve an image reconstruction using the phase-closure technique. We focus this calibration experiment on the interference fringe contrast measurements and the evolution of the phase-closure term versus the differential dispersion effects induced by the stretching of fibre delay lines.

Photocatalytic deposition of a gold nanoparticle onto the top of a SiN cantilever tip.

We propose a new technique for depositing a gold nanoparticle onto the tip of a dielectric support. We employed the photocatalytic effect of titanium dioxide for the deposition. When the titanium dioxide immersed in a solution including gold ions is subject to optical exposure, the excited electrons in the conduction band reduce gold ions into gold metal. Illumination by an evanescent wave generated with a total reflection configuration limits the deposition region to the very tip. In experiments we obtained 100-300 nm gold particles on SiN cantilever tips for atomic force microscopes. The contrast of evanescent interference fringes measured by a near-field scanning optical microscope with this gold nanoparticle probe has proved to be higher than that with a non-deposited SiN probe by a factor of 1.5.