Showing papers on "Interferometry published in 1975"

Observation of Gravitationally Induced Quantum Interference

Abstract: We have used a neutron interferometer to observe the quantum-mechanical phase shift of neutrons caused by their interaction with Earth's gravitational field.

Use of an ac heterodyne lateral shear interferometer with real-time wavefront correction systems.

Abstract: An analysis is performed to determine the accuracy with which an ac heterodyne lateral shear interferometer can measure wavefront aberrations if a white light extended source is used with the interferometer, and shot noise is the predominate noise source. The analysis shows that for uniform circular or square sources larger than a derived minimum size, the wavefront measurement accuracy depends only upon the radiance of the source and not upon the angular subtense of the source. For a 1-msec integration time, a 25-cm(2) collecting area, and a source radiance of 10 W/m(2)-sr the rms wavefront error is approximately 1/30 wave, assuming the signal is shot noise limited. It is shown that for both uniform circular and square sources an optimum shear distance is approximately (1/2) the aperture diameter required to resolve the light source. Comments are made on the optimum shear for nonuniform radiance distributions.

Theory and Application of Point-Diffraction Interferometers

Abstract: The point-diffraction interferometer is an interferometer for measuring phase variations in which the reference wave is produced by a point discontinuity in the path of the beam. Its simplicity makes it very suitable for testing instruments in situ, and some such tests are described. The general theory shows that other diffracting apertures can be used and relates the technique to phase-contrast microscopy and to scatter-plate interferometry.

Interferometric measurements of the nonlinear refractive-index coefficient relative to CS 2 in laser-system-related materials

Abstract: Using time-resolved interferometry, we have compared the nonlinear wavefront distortion induced by the simultaneous propagation of an intense light beam in pertinent sample materials relative to the known reference material. Utilizing several normalization techniques, these measurements have led to precise values for the nonlinear coefficient n 2 good to 10 percent.

Evaluation of large aberrations using a lateral-shear interferometer having variable shear.

Abstract: A variable shear lateral shearing interferometer consisting of two holographically produced crossed diffraction gratings is used to test nonrotationally symmetric wavefronts having aberrations greater than 100 wavelengths and slope variations of more than 400 wavelengths/diameter. Comparisons are made with results of Twyman-Green interferometric tests for wavefront aberrations of up to thirty wavelengths. The results indicate that small wavefront aberrations can be measured as accurately with the lateral-shear interferometer as with the Twyman-Green interferometer and that aberrations that cannot be measured at all with a Twyman-Green interferometer can be measured to about 1% accuracy or better.

Effect of Earth's Rotation in Neutron Interferometry

Abstract: In a neutron interferometer experiment which can successfully demonstrate a quantitative fringe shift due to the different gravitational potential for the neutron in the two legs of the apparatus, an adjunctive consideration must be the nonzero angular velocity of Earth and the lab. As in the classic Michelson-Gale-Pearson experiment done with light, and offset in the fringe pattern is predicted. Such a shift may not be subliminal at present precision levels.

Normal Modes in the Ion-Beam-Plasma System

Abstract: Two types of dispersion relations are experimentally shown to exist in an ion-beam-plasma system. For beam velocities close to the ion-sound speed, two normal modes, one unstable, are seen. For larger beam velocities, the interferometer output exhibits beating between the three predicted stable normal modes, which are the "fast" and "slow" ion-beam modes and the plasma ion-acoustic wave.

Interferometry of strongly refracting axisymmetric phase objects.

Abstract: Inversion of measurements of optical pathlength through strongly refracting, radially symmetric phase objects, such as plasmas, is discussed. An exact inversion scheme, based upon methods originally applied in seismology is developed and applied to interferometry. It is shown that Abel inversion, which assumes that the probing rays are straight lines, yields rather accurate results if the interferogram is formed with appropriate imaging.

Space-invariant achromatic grating interferometers: theory.

Abstract: A general analysis of an n-grating interferometer under various conditions of illumination is presented, where n = 1,...,4. Conditions for fringe localization and effects of misalignment are given. The lesser known phenomenon of the imaging of a grating by a second grating is described from which the fringe forming capacity of multiple-grating interferometers stems; this can occur regardless of the coherence of the source.

Speckle-Shearing Interferometric Technique: a Full-Field Strain Gauge

Abstract: An improved speckle-shearing interferometric method is presented that allows simultaneous determination of derivatives of surface displacements of a structure with respect to four different directions. The technique relaxes several limitations associated with conventional interferometry and thus is adaptable to nonlaboratory environments. The relevant theory is presented, and the method demonstrated by determining spatial derivatives of in-plane and out-of-plane displacements of statically loaded and vibrated structures.

Laser generation of ultrasonic waves for nondestructive testing

Abstract: An object is tested for thickness or for presence and location of flaws by impacting a pulsed laser beam on the surface of the object so as to generate ultrasonic waves by rapid heating of a thin surface layer thereon. The reflected ultrasonic echo in the object is detected by monitoring surface motion with a rough surface interferometer.

Review Lecture: Ten Years of X-Ray Interferometry

Abstract: X-ray interferometers were the first optical instruments which utilized many Bragg reflecting components in monolithic blocks of perfect crystal. They have made important contributions to our knowledge of fundamental constants, of Bragg reflexion X-ray optics, of strains and defects in crystals and of the optical constants of materials in the X-ray region of the electro-magnetic spectrum. Based on an oversimplified optical analogue, their mode of operation is described in detail. Current applications of crystal interferometers and possible future work is briefly reviewed.

Optical waveguide interferometer modulator-switch

Abstract: An optical waveguide arrangement operates in the manner of an interferometer to provide modulator and/or switching functions. Two optical waveguide branches having a common connection diverge along a substantially coextensive distance and reconverge to provide first and second light paths of identical optical length. Conductive electrodes are disposed contiguous to at least one of the optical waveguide branches and are connectable through a controlling switch to a source of electrical energy for producing an electric field across the energized electrodes. In the absence of such electric field, light energy entering the two optical waveguide branches will propagate along identical optical path lengths and recombine constructively at the reconvergence of the waveguide branches. However, a selectively applied electrical energy changes the optical property of at least one of the optical waveguide branches causing phase differences in the optical energy transmitted by the branches and producing destructive interference at the reconvergence of the optical waveguide branches. The addition of two optical waveguide sections having different dimensions provides a switch function when one of such additional waveguides is dimensioned to be conducive to the propagation of first order mode light energy while the other waveguide is dimensioned to be conducive to the propagation of second order mode light energy.

Sandwich hologram interferometry. 2: some practical calculations.

Abstract: Two hologram plates representing different object situations are bonded together with their emulsions separated. Fringes are formed that can be manipulated during reconstruction by moving the sandwich hologram in relation to the reconstruction beam. We have studied practical mathematical relations between sandwich motions, fringe changes, and object motion between the two exposures. Four dimensionless equations have been found that can be used for fringe evaluation by measuring sandwich motions. The wavelength of light is not involved in this new analogous compensating method. In contrast to ordinary double-exposed holograms, the sandwich hologram can directly reveal signs of displacements and maximal object strain.

The refractive index and Lorenz–Lorentz function of fluid methane

Abstract: The refractive index of gaseous and liquid methane was measured between 95 and 300 K and to pressures of 225 bar (1 bar = 105 Pa). The measurements were performed at the 198Hg vapor green line, λ=546.2 nm, with a Fabry–Perot interferometer referred to vacuum. The refractive index data were combined with the previously measured densities of methane to calculate the Lorenz–Lorentz (LL) function. Refractometric virial coefficients were obtained from analysis of the small (∼0.5%) maximum exhibited by the (LL) function with increasing density. BR, the second refractometric virial coefficient, is estimated to be ∼6.0 (cm3/mol)2 and is almost independent of temperature between 220 and 300 K. The critical point refractive index, nc=1.10333, was extrapolated from a rectilinear diameter treatment of the saturated liquid and vapor results. The critical point refractive index was combined with an estimate of the critical point (LL) function to yield a critical density of methane, ρc= 10.16±0.01 mol/l.

Interferometer mirror tilt correcting system

Abstract: An interferometer having servo means for automatically adjusting the angular tilt of a reflecting surface in one of two paths to maintain the exit beams from the two paths parallel to each other. Three detectors at the output of the interferometer are disposed on mutually perpendicular axes which define a plane normal to the nominal exit beam axis. One detector at the origin of the axes is used as a reference for separate phase-difference comparison with the outputs of the other two detectors on the X and Y axes to develop servo error signals.

Sagnac or Michelson-Sagnac interferometer?

Abstract: Apart from the well-known Michelson and Mach-Zehnder interferometers, a third basic type of two-beam interferometer using amplitude division is one in which the two beams traverse the same closed path in opposite directions before they are recombined.' Interferometers of this type are easy to set up and adjust 2 because the number of degrees of freedom available is restricted. 3 4 They offer distinct advantages for some purposes5 and have recently found use in several applications including shearing interferometry,6 -9 holography,10\"'t and optical data processing.12-14 One of the earliest applications of interferometers of this type was in experiments to detect the ether-wind in rotation, such as that carried out by Harress between 1909 and 1911 using a ring interferometer built up of glass prisms. This was described in his thesis15; but because of his untimely death, his experiments were published only in 1920 by Knopf.16 Much of the information on his work is derived only from this paper as well as two later papers by Pogany,' 7\"18 who rebuilt his apparatus with several improvements. The best known series of experiments in this field, however, was that carried out around the same time by Sagnac using an interferometer with a closed pentagonal path mounted on a rotating platform. These were reported in three publications from 1913 to 1914.19-21 Since Sagnac held that the shift of the fringes which he observed con-

Practical Speckle Interferometry for Measuring In-Plane Deformation

Abstract: Speckle interferometry involves making a high resolution double-exposure photograph of an object that is illuminated with coherent light. When observed in a Fourier optical data processor, fringes are observed that are indicative of the changes, such as displacements, occurring in the body between exposures. Sensitivity of the measurement is variable and may be chosen after the data are recorded. A simple calibration procedure is described and its use in measuring in-plane displacements in deformable solids is demonstrated. Also given are some limitations on the range of sensitivity that can be effectively utilized with holographic films, simple procedures, and a small laser.

OTF measurements with a white light source: an interferometric technique

Abstract: The use of lateral shear interferometers for measuring the optical transfer function of an optical system for a white light source is investigated. It is shown that grating lateral shear interferometers fulfill the requirements necessary to perform measurements of both the optical transfer function and the optical coherence function for a white light source. Several possible grating lateral shear interferometers are described.

Analysis of the laser velocity interferometer

Abstract: A rigorous description is presented for the interference of two light beams which have undergone different time delays after reflection from a moving mirror. Conditions relating the optical delay and the motion of the mirror are given that must be satisfied for the usual velocity‐interferometer relations to be valid.

Sample point interferometric system for optical figure monitoring

Abstract: A system for monitoring the optical figure of a surface utilizes an interferometer and a source of light to provide a measuring beam and a reference beam. Reflective spots are mounted respectively at a number of sample points on the surface and the measuring beam of light is focussed by optical means to provide an image field that includes the reflective spots which are oriented to reflect light from the measuring beam back to the optical means to form a conjugate image of the field of spots on light intensity detectors. The reference beam, whose path length is modulated, is combined with the light reflected from the spots to the detectors. There are separate detector elements for measuring the intensity of the combination of reference beam light and measuring beam light reflected from at least two different spots at one time. A shift in position of one sample point forward or back in relation to another sample point, which is a reference point, is thus monitored by comparing the phase relationship of the combination of the reference light with reflected light derived simultaneously from at least a pair of the sample points.

Interferometric navigation and guidance system

Abstract: This invention comprises an interferometric technique for the one-way transmission of bearing angle information to an unlimited number of mobile receivers. In accordance with the invention the angle related path length difference, between transmitters located at either end of an interferometer baseline, to a mobile receiver is measured in wavelengths at a modulation frequency.

Pulsed HF Laser Holographic Interferometry.

Abstract: Two-dimensional holographic interferometry has been accomplished at wavelengths near 3 μm The source is a pulsed hydrogen fluoride oscillator-amplifier system Transverse excitation is achieved with a fast bank discharging into a simple electrode configuration The spatial detector is a thin film of bismuth, exposed by local evaporation by a single line of the HF laser emission spectrum Double exposure interferograms covering areas up to ~10 cm2 in the object plane have been obtained with single-line laser energies of less than a joule

Observations with a VLB array. I. Introduction and procedures

Abstract: A series of observations intended to investigate the structure and the time development of the structure of compact extragalactic radio sources at lambda=2.8 cm and resolution 0''./sub /001 is described. The five telescopes, the sensitivity of the system, the calibration procedures, and modeling procedures are discussed. (AIP)