Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “INTERFEROMETRY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2002

Alignment of optical delay lines for long-baseline stellar interferometry.

The problem of aligning an optical delay line for use in long-baseline stellar interferometry is discussed. particular, the development of the Navy Prototype Optical Interferometer alignment system is described. Rapid mirror alignment must be performed with sufficient precision that beam shear is limited to a few millimeters over an optical path length that may exceed 800 m. Two possible alignment algorithms are presented. The first is a null-seeking servo where the mirrors are adjusted to minimize the sum of their angular alignment errors. The second method utilizes a priori knowledge of the mirror separations to minimize the total shear. A number of time-dependent and time-independent errors that affect alignment and alignment stability are also discussed.

Journal Article↗
PubMed2002

Optimization approach to the suppression of vibration errors in phase-shifting interferometry.

An optimization-based strategy is introduced for suppressing errors due to vibration in phase-shifting-interferometry algorithms. A norm-square integral criterion of the error as a function of vibration frequency is used as the basis of the optimization procedure. Analytical results are obtained for certain classes of problems, and numerical algorithms are used when these are not available. It is also shown that the effect of vibration-induced errors in the computation of a time-averaged phase estimate diminishes as the measurements are averaged. Simulations are used to validate the analysis and demonstrate the overall efficacy of the approach. Generalizations to multiple objective optimization problems are briefly discussed.

Journal Article↗
PubMed2003

Least-squares phase estimation with multiple parameters in phase-shifting electronic speckle pattern interferometry.

We have developed an accurate and robust phase-estimation method in phase-shifting electronic speckle pattern interferometry. Unlike other methods that assume a constant phase within a fitting window, our method treats the phase variation with a gradient. A cost function that can utilize the information of pixel positions is formulated on the basis of a least-squares criterion. Powell's iteration method is applied to it to derive the phase and its gradient. An automatic consistency-checking routine and an algorithm that improves the initial guess of the iteration are developed for severe situations with large noise and steep phase variations.

Journal Article↗
PubMed2004

Investigation of the Cauchy-Riemann equations for one-dimensional image recovery in intensity interferometry.

A method of image recovery using noniterative phase retrieval is proposed and investigated by simulation. This method adapts the Cauchy-Riemann equations to evaluate derivatives of phase based on derivatives of magnitude. The noise sensitivity of the approach is reduced by employing a least-mean-squares fit. This method uses the analytic properties of the Fourier transform of an object, the magnitude of which is measured with an intensity interferometer. The solution exhibits the degree of nonuniqueness expected from root-flipping arguments for the one-dimensional case, but a simple assumption that restricts translational ambiguity also restricts the space of solutions and permits essentially perfect reconstructions for a number of non-symmetric one-dimensional objects of interest. Very good reconstructions are obtained for a large fraction of random objects, within an overall image flip, which may be acceptable in many applications. Results for the retrieved phase and recovered images are presented for some one-dimensional objects and for different noise levels. Extensions to objects of two dimensions are discussed. Requirements for signal-to-noise ratio are derived for intensity interferometry with use of the proposed processing.

Journal Article↗
PubMed2004

Theoretical and experimental evaluation of the modal field shift and the associated transition loss in perturbed index-profile single-mode optical fiber with application of Fizeau interferometry.

Fizeau micro-interferometry is applied to evaluate some parameters of a curved single-mode optical fiber. The field shift of the fundamental mode and the associated transition loss in a perturbed index-profile fiber due to bending are determined. The preceding fiber parameters are determined as a function of the shift of multiple-beam Fizeau fringes. For a curvature range between 0.13 and 0.053 mm(-1), a range of field shift between 0.44 and 0.21 microm is determined. A fraction of the transition loss ranging between 0.0056 and 0.028 is calculated within the same curvature range. Because our method has high index resolution and spatial resolution, it shows good agreement with theory. The results and the agreement with theory indicate that the use of multiple-beam Fizeau fringes is a promising technique that is capable of determining with high accuracy some guidance parameters of the optical fibers.

Journal Article↗
PubMed2005

Rotational invariance approach for the evaluation of multiple phases in interferometry in the presence of nonsinusoidal waveforms and noise.

Incorporation of two phase-shifting devices in a holographic moiré configuration not only renders the interferometer compatible with automated measurements but also allows for simultaneous measurement of multiple phase information in the interferometer. However, simultaneous handling of multiple phase steps and subsequent simultaneous determination of multiple phase distributions requires the introduction of novel tools in phase-shifting interferometry. In this context, the aim of this paper is to propose a subspace invariance approach to address these issues. This approach takes advantage of the rotational invariance of signal subspaces spanned by two temporally displaced data sets formed from the intensity fringes recorded temporally on pixels of the CCD camera. The method first identifies the arbitrary phase steps imparted to the piezoactuator devices. The estimated phase steps are subsequently applied in the linear Vandermonde system of equations to determine the phase distributions. The method also allows for handling nonsinusoidal wavefronts. Since the phase steps are extracted at every point on the interferogram, the method is applicable to configurations that use spherical beams. The robustness of the method is investigated by adding white Gaussian noise during the simulations.

Journal Article↗
PubMed2005

Iterative algorithm for subaperture stitching interferometry for general surfaces.

A novel iterative algorithm for subaperture stitching interferometry for general surfaces is presented. It is based on the alternating optimization technique and the successive linearization method. The computer-aided-design model of the tested surface is used to determine the overlapping region precisely. Subapertures are simultaneously stitched by minimizing deviations among them as well as deviations from the nominal surface. Precise prior knowledge of the six degrees-of-freedom nulling and alignment motion is no longer required.

Journal Article↗
PubMed2005

Spatial phase-shift interferometry--a wavefront analysis technique for three-dimensional topometry.

We describe a new wavefront analysis method, in which certain wavefront manipulations are applied to a spatially defined area in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing methods, making this method a spatial phase-shift interferometry method. We demonstrate the system's dependence on a defined spatial Airy number, which is the ratio of the characteristic dimension of the manipulated area and the Airy disk diameter of the optical system. We analytically obtain the resulting intensity data of the optical setup and develop various methods to accurately reconstruct the inspected wavefront out of the data. These reconstructions largely involve global techniques, in which the entire wavefront's pattern affects the reconstruction of the wavefront in any given position. The method's noise sensitivity is analyzed, and actual reconstruction results are presented.

Journal Article↗
PubMed2006

Fiber-based single-channel polarization-sensitive spectral interferometry.

We present a novel, to our knowledge, fiber-based single-channel polarization-sensitive spectral interferometry system that provides depth-resolved measurement of polarization transformations of light reflected from a sample. Algebraic expressions for the Stokes parameters at the output of the interferometer are derived for light reflected from a birefringent sample by using the cross-spectral density function. By insertion of a fiber-optic spectral polarimetry instrument into the detection path of a common-path spectral interferometer, the full set of Stokes parameters of light reflected from a sample can be obtained with a single optical frequency scan. The methodology requires neither polarization-control components nor prior knowledge of the polarization state of light incident on the sample. The fiber-based single-channel polarization-sensitive spectral interferometer and analysis are demonstrated by measurement of phase retardation and fast-axis angle of a birefringent mica plate.

Journal Article↗
PubMed2003

Single-shot kilohertz characterization of ultrashort pulses by spectral phase interferometry for direct electric-field reconstruction.

We describe a method of characterizing ultrashort optical pulses that is based on the technique of spectral phase interferometry for direct electric-field reconstruction and is capable of simultaneously measuring the amplitude and the phase of the electric field of a sub-10-fs pulse at kilohertz acquisition rates on a single-shot basis. Use of this technique results in a dramatic increase (>50x) in acquisition rate compared with that of existing diagnostics for full E-field characterization and opens the door to a range of new experiments in which shot-to-shot phase and amplitude fluctuations are studied at kilohertz rates.

Journal Article↗
PubMed2003

Wave-front phase measurements of high-order harmonic beams by use of point-diffraction interferometry.

We report the wave-front phase measurement of high-order harmonics employing point-diffraction interferometry. The high-order harmonics generated in a gas-filled hollow tube showed excellent spatial coherence over nearly the whole cross section of the harmonic beams. Using this coherent harmonic source in the extreme-ultraviolet-soft-x-ray region, we have demonstrated the operation of a point-diffraction interferometer and measured the wave-front phase of high-order harmonics.

Journal Article↗
PubMed2003

Optimum frequency selection in multifrequency interferometry.

We describe a novel technique for measurement of absolute order of interference in multifrequency interferometry. An optimization criterion is introduced that leads to frequency selection formulations that are optimized with respect to the minimum number of frequencies required for achieving the maximum target dynamic range. The method is generalized to N frequencies and gives a definition of measurement reliability. We demonstrate the technique by means of coherent fringe projection for nonintrusive, full-field profilometry. Experimental data for three frequencies are presented.

Journal Article↗
PubMed2003

Phase-shift extraction and wave-front reconstruction in phase-shifting interferometry with arbitrary phase steps.

A new approach to reconstructing the object wave front in phase-shifting interferometry with arbitrary unknown phase steps is proposed. With this method the actual phase steps are first determined from measured intensities with an algorithm based on the statistic property of the object phase distribution in the recording plane. Then the original object field is calculated digitally with a derived formula. This method is simple, accurate, and capable of retrieving the original object field, including its amplitude and phase distributions simultaneously, with arbitrary and unequal phase steps in a three- or four-frame method. The effectiveness and correctness of this approach are verified by a series of computer simulations for both smooth and diffusing surfaces.

Journal Article↗
PubMed2003

Implementation of electro-optic spectral shearing interferometry for ultrashort pulse characterization.

Electro-optic spectral shearing interferometry is implemented for the highly sensitive characterization of ultrashort pulses from a free-running source. A simple phase-locked-loop clock recovery circuit is used to extract the high-frequency microwave clock signal to drive the phase modulator for spectral shearing. We demonstrate accurate full temporal characterization of 200-fs pulses from an optical parametric oscillator at 5-pW average power.

Journal Article↗
PubMed2003

Ponderomotive shearing for spectral interferometry of extreme-ultraviolet pulses.

We propose a novel method for completely characterizing ultrashort pulses at extreme-ultraviolet (XUV) wavelengths by adapting the technique of spectral phase interferometry for direct electric-field reconstruction to this spectral region. Two-electron wave packets are coherently produced by photoionizing atoms with two time-delayed replicas of the XUV pulse. For one of the XUV pulses, photoionization occurs in the presence of a strong infrared pulse that ponderomotively shifts the binding energy, thereby providing the spectral shear needed for reconstruction of the spectral phase of the XUV pulse.

Journal Article↗
PubMed2004

Common-path interferometry with one-dimensional periodic filters.

We discuss a spatial filtering interferometry setup that employs a periodic spatial filter with either cosine transmittance or binary phase modulation. The setup's input plane is formed by two separate windows, one of which supports a phase object and the other, a reference beam. Using the appropriate frequency and orientation of the filter produces an interference pattern of the two input fields at the output plane of the system. The main attributes and advantages of the setup are discussed and experimentally illustrated with the example of a binary phase periodic filter implemented with a spatial light modulator.

Journal Article↗