Showing papers on "Interferometry published in 2005"

X-ray phase imaging with a grating interferometer.

Abstract: Using a high-efficiency grating interferometer for hard X rays (10-30 keV) and a phase-stepping technique, separate radiographs of the phase and absorption profiles of bulk samples can be obtained from a single set of measurements. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index, with a spatial resolution down to a few microns. The method is mechanically robust, requires little spatial coherence and monochromaticity, and can be scaled up to large fields of view, with a detector of correspondingly moderate spatial resolution. These are important prerequisites for use with laboratory X-ray sources.

Matter-wave interferometry in a double well on an atom chip

Abstract: Matter-wave interference experiments enable us to study matter at its most basic, quantum level and form the basis of high-precision sensors for applications such as inertial and gravitational field sensing. Success in both of these pursuits requires the development of atom-optical elements that can manipulate matter waves at the same time as preserving their coherence and phase. Here, we present an integrated interferometer based on a simple, coherent matter-wave beam splitter constructed on an atom chip. Through the use of radio-frequency-induced adiabatic double-well potentials, we demonstrate the splitting of Bose–Einstein condensates into two clouds separated by distances ranging from 3 to 80 μm, enabling access to both tunnelling and isolated regimes. Moreover, by analysing the interference patterns formed by combining two clouds of ultracold atoms originating from a single condensate, we measure the deterministic phase evolution throughout the splitting process. We show that we can control the relative phase between the two fully separated samples and that our beam splitter is phase-preserving.

High resolution optical frequency domain reflectometry for characterization of components and assemblies.

Abstract: We describe a technique for polarization sensitive optical frequency domain reflectometry (OFDR) that achieves 22 micrometer two-point spatial resolution over 35 meters of optical length with -97 dB sensitivity in a single measurement taking only seconds. We demonstrate OFDR’s versatility in both time- and frequency-domain metrology by analyzing a fiber Bragg grating (FBG) in both the spectral and impulse response domains. We also demonstrate how a polarization diversity receiver can be used in an OFDR system to track changes in the polarization state of light propagating through a birefringent component.

Real-time fiber-based multi-functional spectral-domain optical coherence tomography at 1.3 mu m

Abstract: We demonstrate a high-speed multi-functional spectral-domain optical coherence tomography system, using a broadband light source centered at 1.3 µm and two InGaAs line scan cameras capable of acquiring individual axial scans in 24.4 µs, at a rate of 18,500 axial scans per second. Fundamental limitations on the accuracy of phase determination as functions of signal-to-noise ratio and lateral scan speed are presented and their relative contributions are compared. The consequences of phase accuracy are discussed for both Doppler and polarization-sensitive OCT measurements. A birefringence artifact and a calibration procedure to remove this artifact are explained. Images of a chicken breast tissue sample acquired with the system were compared to those taken with a time-domain OCT system for birefringence measurement verification. The ability of the system to image pulsatile flow in the dermis and to perform functional imaging of large volumes demonstrates the clinical potential of multi-functional spectral-domain OCT.

Optical-Fiber Source of Polarization-Entangled Photons in the 1550 nm Telecom Band

Abstract: We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.

Mach-Zehnder Interferometry in a Strongly Driven Superconducting Qubit

Abstract: We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, the ground and excited states of which exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. Because the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n = 1 to 20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime.

Attosecond double-slit experiment.

Abstract: A new scheme for a double-slit experiment in the time domain is presented. Phase-stabilized few-cycle laser pulses open one to two windows (slits) of attosecond duration for photoionization. Fringes in the angle-resolved energy spectrum of varying visibility depending on the degree of which-way information are measured. A situation in which one and the same electron encounters a single and a double slit at the same time is observed. The investigation of the fringes makes possible interferometry on the attosecond time scale. From the number of visible fringes, for example, one derives that the slits are extended over about 500 as.

Atom Michelson Interferometer on a Chip Using a Bose-Einstein Condensate

Abstract: An atom Michelson interferometer is implemented on an ``atom chip.'' The chip uses lithographically patterned conductors and external magnetic fields to produce and guide a Bose-Einstein condensate. Splitting, reflecting, and recombining of condensate atoms are achieved by a standing-wave light field having a wave vector aligned along the atom waveguide. A differential phase shift between the two arms of the interferometer is introduced by either a magnetic-field gradient or with an initial condensate velocity. Interference contrast is still observable at 20% with an atom propagation time of 10 ms.

Spectral-domain optical coherence phase microscopy for quantitative phase-contrast imaging.

Abstract: We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial cheek cells.

Spectral Domain Phase Microscopy

Abstract: Broadband interferometry is an attractive technique for the detection of cellular motions because it provides depth-resolved phase information via coherence gating. We present a phase-sensitive technique called spectral-domain phase microscopy (SDPM). SDPM is a functional extension of spectral-domain optical coherence tomography that allows for the detection of nanometer-scale motions in living cells. The sensitivity of the technique is demonstrated, and its calibration is verified. A shot-noise limit to the displacement sensitivity of this technique is derived. Measurement of cellular dynamics was performed on spontaneously beating cardiomyocytes isolated from chick embryos.

Instantaneous complex conjugate resolved spectral domain and swept-source OCT using 3x3 fiber couplers

Abstract: We report that the complex conjugate artifact in Fourier domain optical coherence tomography approaches (including spectral domain and swept source OCT) may be resolved by the use of novel interferometer designs based on 3x3 and higher order fiber couplers. Interferometers built from NxN (N>2) truly fused fiber couplers provide simultaneous access to non-complementary phase components of the complex interferometric signal. These phase components may be converted to quadrature components by trigonometric manipulation, then inverse Fourier transformed to obtain A-scans and images with resolved complex conjugate artifact. We demonstrate instantaneous complex conjugate resolved Fourier domain OCT using 3x3 couplers in both spectral domain and swept source implementations. Complex conjugate artifact suppression by factors of ~20dB and ~25dB are demonstrated for spectral domain and swept source implementations, respectively.

Differential tomography: a new framework for SAR interferometry

Abstract: A new interferometric mode crossing the differential synthetic aperture radar (SAR) interferometry and multibaseline SAR tomography concepts, that can be termed differential SAR tomography, is proposed. Its potentials, coming from the joint elevation-velocity resolution capability of multiple scatterers, are discussed. Processing is cast in a bidimensional baseline-time spectral analysis framework, with sparse sampling. The use of a modern data-dependent bidimensional spectral estimator is proposed for joint baseline-time processing. Simulated results are reported for different baseline-time acquisition patterns and two motion conditions of layover scatterers, showing that this new challenging interferometric technique is promising.

Accuracy of differential shift estimation by correlation and split-bandwidth interferometry for wideband and delta-k SAR systems

Abstract: Estimation of differential shift of image elements between two synthetic aperture radar (SAR) images is the basis for many applications, like digital elevation model generation or ground motion mapping. The shift measurement can be done nonambiguously on the macro scale at an accuracy depending on the range resolution of the system or on the micro scale by employing interferometric methods. The latter suffers from phase cycle ambiguities and requires phase unwrapping. Modern wideband high-resolution SAR systems boast resolutions as small as a few tens of a wavelength. If sufficiently many samples are used for macro-scale shift estimation, the accuracy can be increased to a small fraction of a resolution cell and even in the order of a wavelength. Then, accurate absolute ranging becomes precise enough to support phase unwrapping or even make it obsolete. This letter establishes a few fundamental equations on the accuracy bounds of shift estimation accuracy for several algorithms: coherent speckle correlation, incoherent speckle correlation, split-band interferometry, a multifrequency approach, and correlation of point scatterers in clutter. It is shown that the performance of split-band interferometry is close to the Crame/spl acute/r-Rao bound for a broad variety of bandwidth ratios. Based on these findings, Delta-k systems are proposed to best take advantage of the available radar bandwidth.

Swept source optical coherence tomography using an all-fiber 1300-nm ring laser source.

Abstract: The increased sensitivity of spectral domain optical coherence tomography (OCT) has driven the development of a new generation of technologies in OCT, including rapidly tunable, broad bandwidth swept laser sources and spectral domain OCT interferometer topologies. In this work, the operation of a turnkey 1300-nm swept laser source is demonstrated. This source has a fiber ring cavity with a semiconductor optical amplifier gain medium. Intracavity mode selection is achieved with an in-fiber tunable fiber Fabry-Perot filter. A novel optoelectronic technique that allows for even sampling of the swept source OCT signal in k space also is described. A differential swept source OCT system is presented, and images of in vivo human cornea and skin are presented. Lastly, the effects of analog-to-digital converter aliasing on image quality in swept source OCT are discussed.

Analysis of a micropolarizer array-based simultaneous phase-shifting interferometer

Abstract: Recent technological innovations have enabled the development of a new class of dynamic (vibration-insensitive) interferometer based on a CCD pixel-level phase-shifting approach We present theoretical and experimental results for an interferometer based on this pixelated phase-shifting technique Analyses of component errors and instrument functionality are presented We show that the majority of error sources cause relatively small magnitude peak-to-valley errors in measurement of the order of 0002-0005lambda These errors are largely mitigated by high-rate data acquisition and consequent data averaging

Detection of Acoustic Oscillations of Single Gold Nanospheres by Time-Resolved Interferometry

Abstract: We measure the transient absorption of single gold particles with a common-path interferometer. The prompt electronic part of the signal provides images for diameters as small as 10 nm. Mechanical vibrations of single particles appear on a longer time scale (period of 16 ps for 50 nm diameter). They reveal the full heterogeneity of the ensemble, and the intrinsic damping of the vibration. We also observe a lower-frequency mode involving shear. Ultrafast pump-probe spectroscopy of individual particles opens new insight into mechanical properties of nanometer-sized objects.

Ultra-miniature fiber-optic pressure sensor using white light interferometry

Abstract: We have developed a fiber-optic Fabry–Perot interferometric pressure sensor of 125 µm in diameter and a detection system for medical use. A Fabry–Perot cavity is formed at an optical fiber end. A deformation of the diaphragm of the Fabry–Perot cavity induced by pressure varies the cavity length. White light interferometry is used to avoid error and noise caused by bending of the optical fiber and fluctuation of the light source. The reflection light of the sensor cavity is detected by a commercial high-speed spectrometer. A pressure change has been detected by using the developed sensor system. Animal experiments using a goat have been carried out and dynamic pressure changes in the internal pressure of heart and aorta have been successfully monitored.

X-ray wavefront analysis and optics characterization with a grating interferometer

Abstract: We present an interferometric method to measure the shape of a hard-x-ray wavefront. The interferometer consists of a phase grating as a beam splitter and an absorption grating as a transmission mask for the detector. The device can be used to measure wavefront shape gradients corresponding to radii of curvature as large as several dozens of meters, with a lateral resolution of a few microns. This corresponds to detected wavefront distortions of approximately 10−12m or λ∕100. The device was used with 12.4 keV x rays to measure the slope error and height profile of an x-ray mirror. Surface slope variations with periods ranging from less than 1 mm to more than 1 m can be detected with an accuracy better than 0.1μrad.

Method and device for multistate interferometric light modulation

Abstract: A multi-state light modulator comprises a first reflector. A first electrode is positioned at a distance from the first reflector. A second reflector is positioned between the first reflector and the first electrode. The second reflector is movable between an undriven position, a first driven position, and a second driven position, each having a corresponding distance from the first reflector. In one embodiment, the three positions correspond to reflecting white light, being non-reflective, and reflecting a selected color of light. Another embodiment is a method of making the light modulator. Another embodiment is a display including the light modulator.

Measurement of the sensitivity function in time-domain atomic interferometer

Abstract: We present here an analysis of the sensitivity of a time-domain atomic interferometer to the phase noise of the lasers used to manipulate the atomic wave-packets. The sensitivity function is calculated in the case of a three pulse Mach-Zehnder interferometer, which is the configuration of the two inertial sensors we are building at BNM-SYRTE. We successfully compare this calculation to experimental measurements. The sensitivity of the interferometer is limited by the phase noise of the lasers, as well as by residual vibrations. We evaluate the performance that could be obtained with state of the art quartz oscillators, as well as the impact of the residual phase noise of the phase-lock loop. Requirements on the level of vibrations is derived from the same formalism.

Simple interferometric technique for generation of a radially polarized light beam.

Abstract: We present a theoretical and experimental investigation of an interferometric technique for converting a linearly polarized Gaussian beam into a radially polarized doughnut beam. The experimental setup accomplishes the coherent summation of two orthogonally polarized TEM01 and TEM10 beams that are obtained from the transformation of a TEM00 beam by use of a simple binary diffractive optical element. We have shown that the degree of radial polarization is maximum at a given distance from the interferometer output port that depends on the diameter of the incident beam at the interferometer input port.

Permanent scatterers analysis for atmospheric correction in ground-based SAR interferometry

Abstract: Ground-based synthetic aperture radar (GB-SAR) interferometry has already been recognized as a powerful tool, complementary or alternative to spaceborne SAR interferometry, for terrain monitoring, and for detecting structural changes in buildings. It has been noted that, in spite of the very short range, compared with the satellite configuration, in GB-SAR measurement the disturbances due to atmospheric effects cannot be neglected either. The analysis of the interferometric phases of very coherent points, called permanent scatterers (PSs), allows the evaluation of the atmospheric disturbance and the possibility of removing it. In this paper, the PS analysis is carried out both on a test site facility and on a real campaign (Citrin Valley, Italy) that provided data with a temporal baseline of about ten months.

Sapphire-fiber-based white-light interferometric sensor for high-temperature measurements

Abstract: We present a fiber-optic temperature sensor with a single-crystal sapphire fiber as the light guide and a sapphire wafer as the sensing element. Temperature is determined by measurement of the thermal dependence of the wafer's optical thickness by use of white-light interferometry. We applied digital signal processing techniques to analyze the sensor's spectrum. A prototype sensor was tested to 1600 degrees C and demonstrated excellent reproducibility. An accuracy of +/- 0.2% full scale was obtained. The sensor is simple, small, and flexible, with potential advantages of batch fabrication and easy calibration.

Power spectrum sensitivity and the design of epoch of reionization observatories

Abstract: Recent theoretical developments for observing the epoch of reionization (EOR) have concentrated on the power spectrum signature of redshifted 21 cm emission. These studies have demonstrated the great potential of statistical EOR observations; however, the sensitivity calculations for proposed low-frequency radio arrays have been highly approximate. The formalism developed for interferometric measurements of the cosmic microwave background can be extended to three dimensions to naturally incorporate the line-of-sight information inherent in the EOR signal. In this paper we demonstrate how to accurately calculate the EOR power spectrum sensitivity of an array and develop scaling relationships that can be used to guide the design of EOR observatories. The implications for antenna distribution, antenna size, and correlator requirements on the EOR sensitivity are detailed.

Time-Delay Interferometry

Abstract: Equal-arm detectors of gravitational radiation allow phase measurements many orders of magnitude below the intrinsic phase stability of the laser injecting light into their arms. This is because the noise in the laser light is common to both arms, experiencing exactly the same delay, and thus cancels when it is differenced at the photo detector. In this situation, much lower level secondary noises then set the overall performance. If, however, the two arms have different lengths (as will necessarily be the case with space-borne interferometers), the laser noise experiences different delays in the two arms and will hence not directly cancel at the detector. In order to solve this problem, a technique involving heterodyne interferometry with unequal arm lengths and independent phase-difference readouts has been proposed. It relies on properly time-shifting and linearly combining independent Doppler measurements, and for this reason it has been called time-delay interferometry (TDI). This article provides an overview of the theory, mathematical foundations, and experimental aspects associated with the implementation of TDI. Although emphasis on the application of TDI to the Laser Interferometer Space Antenna (LISA) mission appears throughout this article, TDI can be incorporated into the design of any future space-based mission aiming to search for gravitational waves via interferometric measurements. We have purposely left out all theoretical aspects that data analysts will need to account for when analyzing the TDI data combinations.

Compact 1 × N thermo-optic switches based on silicon photonic wire waveguides

Abstract: Using silicon photonic wire waveguides, we constructed compact 1 × 1, 1 × 2, and 1 × 4 Mach-Zehnder interferometer type optical switches on a silicon-on-insulator substrate and demonstrated their switching operations through the thermo-optic effect These switches were smaller than 140 × 65, 85 × 30, and 190 × 75 μm, respectively At a 1550-nm wavelength, we obtained an extinction ratio larger than 30 dB, a switching power as low as 90 mW, and a switching response time of less than 100 μs Furthermore, switching operations were successfully demonstrated for the 1 × 4 switch

Single-pulse phase-control interferometric coherent anti-Stokes Raman scattering spectroscopy

Abstract: In coherent anti-Stokes Raman scattering (CARS) spectroscopy experiments, usually the amplitude of the signal is measured and the phase information is lost. With a polarization- and phase-controlled pulse shaping technique, the relative phase between the resonant and nonresonant CARS signals is controlled, and spectral interferometry is performed without an interferometer. Both the real and imaginary parts of the background-free resonant CARS spectrum are measured via spectral interferometry between the resonant and nonresonant signals from the same sample. The resonant signal is amplified significantly by homodyne mixing with the nonresonant signal as a local oscillator, greatly improving the detection limit.