Showing papers on "Wavefront published in 1972"

Using Computer Generated Holograms to Test Aspheric Wavefronts

Abstract: The use of computer generated holograms for the testing of aspheric wavefronts is described. An analysis of the errors produced by emulsion movement, incorrect hologram size and position, and distortion in hologram plotter and photoreduction lens is given, and it is shown that all the errors are proportional to the slope of the aspheric wavefront. Experimental results verifying the error analysis are shown for testing rotationally nonsymmetric wavefronts having slopes as large as 125 waves per radius and departures as large as sixty-five waves.

Interference microscopy of polymer fibres

Abstract: SUMMARY The paper describes the use of a double refracting interference microscope with variable amount and direction of wavefront shear for the study of synthetic polymer fibres. General theoretical aspects of the field of the differential interference contrast method, and practical problems related to the application of this method in fibre examination are discussed. Some improvements in the micro-interferometric measurement of the birefringence and refractive indices of fibres are suggested. Advantages of the developed double refracting interference microscope with variable wavefront shear are discussed from the point of view of fibre microscopy, and illustrated by photomicrographs.

Acoustic abatement method and apparatus

Abstract: An acoustic receiver, amplifier and transmitter generate an anti wave which is in-phase and of mirror symmetry with respect to a propagating acoustic wave. Coherent propagation means such as an acoustic duct of particular dimensions redirects and/or converts the acoustic wave and the anti wave, which otherwise propagate with incremental wavefronts at different vectors, into plane waves which are superimposed to create wave interference which itself propagates. For noise of high sound pressure level such as created by a gas turbine engine, the acoustic transmitter comprises a modulated gas flow speaker coupled to one or more bleed ports which supply gas at one or more pressures offset from ambient pressure.

Polarization Transfer Function of an Optical System as a Bilinear Transformation

Abstract: The polarization states of light incident on and emerging from an optical system are represented by complex numbers χ¯ and ξ¯, respectively, in two different planes. In this representation, the input–output transfer function ξ¯=f(χ¯) is a conformal bilinear transformation with coefficients given by the elements of the system’s Jones matrix. From the known properties of the bilinear transformation, important conclusions can be reached on the response of optical systems to incident light of all possible polarization forms. In addition, the analysis appears to have considerable potential in the synthesis of systems to effect a prescribed polarization transfer. As an example, the ellipsometer is analyzed by use of some of the ideas developed.

Ionizing potential waves and high-voltage breakdown streamers.

Abstract: The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.

The application of computer-generated holograms to testing optical elements

Abstract: The application of computer-generated holograms to the interferometric testing of aspheric reflecting elements and spherical refracting elements has been investigated. A new technique for calculating the hologram and drawing it with a computer-controlled plotter has been demonstrated to provide holograms that reconstruct the required wavefront with an RMS error of better than ?/20, and interferometers developed that employ the holograms in a null-test of optical elements without impairing this accuracy.

Interferometric testing of large optical components with circular computer holograms

Abstract: In testing a large aspheric mirror such as a paraboloid, one uses as interferometric reference a small spherical mirror together with a test glass. The combination of mirror and test glass produces a parabolic wavefront for comparison. Recently holograms have been used as synthetic test glasses. The average fringe distance of the grating-like holograms has to be fine enough if separation of the diffraction orders is required. We propose to use holograms with circular fringes. Now the different diffraction orders come to focus at different locations on the optical axis, where all but one order can be eliminated. This is easily possible, since the waves coming from a mirror with a central hole are hollow cones. Several ways for making these computer-generated circular holograms are suggested.

Scattering of a Transient Acoustic Wave by an Elastic Cylindrical Shell

Abstract: A plane acoustic step wave traveling through an infinite fluid medium is scattered by an infinite, elastic, circular cylindrical shell whose axis is parallel to the wavefront of the incident wave. The resulting transient acoustic field is studied through the use of temporal convolution techniques in conjunction with wave front analysis. Computed pressure histories are presented for various points in the fluid. The field produced by the cylindrical shell is compared with those produced by a fixed rigid cylinder and a cylindrical cavity. Attention is given to the nearfield pressure reduction capability of the cavity.

Improved Electrostatic Probe for Measurement of Elastic Surface Waves

Abstract: The phase and amplitude distribution of elastic surface waves on piezoelectric substrates may be measured by means of an electrostatic surface probeof the type originally dcmonstrated by Kichardson and Kino ( 11 . An improved version of the electrostatic probe is described and the opera- tion of this device is analyzed. Two unique display techniques allow rapid and straighforward analysis of wavefront distortion for surface waves. Measurements of the propagation character- istics ofZ-directed waves on Y-cut lithium niobate are presented.

Synthesis of Complex Optical Wavefronts

Abstract: For any coding scheme designed for the synthesis of an optical wavefront by a computer-generated, amplitude-transmittance hologram, two types of synthetic holograms may be defined: the first is the encoded form of the optical wavefront itself; the second is the encoded form of the Fourier transform of the wavefront. The extent of the optical wavefront produced by the first type varies inversely, while that of the second type varies directly, with resolution. Five coding schemes are characterized by two important quantities: the first is the minimum number of samples that must be numerically evaluated and drawn; the second is the product of the minimum resolution (lines/unit length) and length (per dimension) required for the drawing. These quantities are a measure of the required computer and drawing device capabilities, respectively, and knowledge of them permits comparison of the coding schemes.

Method and apparatus for recording and projecting holograms

Abstract: A method and apparatus for recording and projecting single color or multiple color encoded image-plane carrier holograms are described. An object is illuminated with a coherent collimated laser beam. The parallel spatially modulated rays are focused on a monochrome recording medium located in a recording plane with the rays maintained essentially parallel. A collimated reference beam, which is coherent with the object beam, is directed at the recording medium to form an image-plane hologram having a single discrete spatial carrier frequency in case of a single color laser or additional spatial carrier frequencies for as many colors as are in the laser. The processed image-plane hologram is projected by directing a generally collimated beam of incoherent white light upon the hologram to form separated wavefront reconstructions of parallel rays. A lens projects the parallel rays in a viewing plane after their convergence at a focal spot in a focal plane. A spatial filter located in the focal plane provides selection of desired color images and blocks undesired ghosts. A control for moving and adjustment of the spatial filter is provided to attain hue and saturation control as well as brightness of the projected image. An embodiment for recording of image-plane holograms of diffuse objects or diffusely illuminated objects as well as three-dimensional objects is described.

Interferometer for testing telescope optics

Abstract: This is an interferometer of Twyman-Green type adapted for testing the optics of a stellar telescope. Coherent light from a source, such as a star, through the telescope is collimated and divided into a reference beam, and a main beam, which are, respectively, a fractional cross-sectional area of the collimated beam, and the remaining cross-sectional area thereof. The reference beam is expanded to be the same diameter as the main beam by an afocal telescope and the two are then combined in superimposed relation. The optical path lengths of the reference and main beams are made approximately the same and means is provided for cyclically lengthening and shortening the length of one of them at a predetermined rate so that one of the paths is cyclically shorter than, equal to and longer than the other. The combined beams are filtered and focussed to image the telescope pupil (usually the primary mirror) in a plane, and at least a pair of photodetectors in this plane detect the light respectively at different points on the image, and produce signals proportional to the light received. The signals from the respective photodetectors are compared as to phase when the signal is sinusoidal, or time delay when the signal is a pulse, to detect the deviation of the wavefront exiting the telescope from the ideal wavefront, such deviation being linearly proportional to aberrations of the telescope resulting from poor optical figure on the individual optical elements or misalignment of the telescope optics.

Acoustic surface wave device

Abstract: An acoustic surface wave device for delay line and filter applications and the like, the device being of the type having spaced couplers or transducers disposed on a surface wave propagating surface of a solid medium and, in order to significantly reduce undesired and generally degrading spurious signals arising from specular reflections from the transducers, the device further includes a surface wave acoustic wavefront rotating member disposed in the path of the surface wave between the transducers.

Experimental Investigation of a Holographic System that Records Front Surface Detail from a Scene Moving at High Velocities.

Abstract: Any motion of the scene during the exposure of a hologram results in a spatial modulation of the recorded fringe contrast. On reconstruction, this produces a spatial amplitude modulation of the reconstructed wavefront, which results in blurring of the image not unlike that of a conventional photograph. The concept of motion holography has been aptly described theoretically by D. B. Neumann. This paper presents and discusses the experimental investigation of a new holographic technique that allows resolution of front surface detail for scene velocities on the order of 9 × 105 cm/sec.

Progress in holography

Abstract: With the award of the 1971 Nobel prize in physics to Dennis Gabor, holography has reached a new pinnacle of prestige. Gabor won his prize for the invention of holography, a form of wavefront reconstruction in which a coherent reference wave appears to unlock a three‐dimensional replica of an object from a two‐dimensional standing‐wave pattern.

Bragg Imaging with Finite Amplitude Ultrasonic Waves

Abstract: Light passing through ultrasonic waves of finite amplitude at the angle at which Bragg diffraction is dominant produces diffraction orders which contain images of the ultrasonic wavefront, with multiple images appearing in the higher orders. These multiple images are attributed to multiple scattering of light by the fundamental ultrasonic wave. The harmonics of the ultrasonic wave arising from nonlinearity of the propagating medium are isolated by use of a transmission filter plate. The images produced by them are larger than those produced by the fundamental.

Series Solution for Electromagnetic Wave Propagation in Radially and Axially Nonuniform Media: Geometrical-Optics Approximation

Abstract: This paper presents a series solution for electromagnetic wave propagation in a medium in which the dielectric constant is given by ∊ = ∊0 − ∊2 (z)r2, without recourse to the WKB approximation. The results have been put in a form suitable for numerical computation. Explicit expression has been obtained for the irradiance distribution in the paraxial region, when the incident wave front is plane gaussian. These investigations are applicable to propagation of laser beams in self-focusing fibers/rods.

Elastic waves in a prestressed Mooney material

Abstract: The dynamic response of a prestressed incompressible Mooney material is studied by investigating plane wave propagation and the response of the material to impulsive lines of force The choice of an initial deformation which is axially symmetric gives a particularly simple form for the secular equation for the plane wavefront velocities The speeds of propagation and the amplitudes of the two permissible transverse waves are found and necessary and sufficient conditions for there to exist two real wave speeds in all directions are established The simple form of the secular equation enables the response of the material to concentrated disturbances to be readily solved using Fourier transforms The motions caused by a line of impulsive forces is examined in some detail

Solution near the wavefront of transient fields in inhomogeneous dispersive media

Abstract: Uniform asymptotic representations, valid in the vicinity of the wavefront, are derived for transient fields propagating in an inhomogeneous dispersive medium. When the space-time ray equations for these fields can be solved explicitly, the uniform representations yield explicit expressions in the space-time variables; otherwise, the representations involve a parameter which can, however, be eliminated under more restrictive conditions. The results are applied to plane pulse propagation in a plane stratified plasma with exponential variation of electron density, for which the space-time ray equations can be solved in closed form; in this case, the asymptotic representation is found to yield the known exact solution.

Differential Interference Contrast Microscope with Continuously Variable Wavefront Shear and Pupilar Compensation

Abstract: A trans-illumination double-refracting interference microscope with pupilar compensation and continuously variable amount of wavefront shear has been developed. A combination of two birefringent prisms separated by a half-wave plate is placed in the image space of the objective. One of these prisms is, together with the half-wave plate, rotatable round the objective axis. This enables the amount of wavefront shear to be changed. The other prism can be translated in a direction perpendicular to the microscope axis. This translation serves for shifting the phase of interfering light waves. Construction parameters of both prisms are fixed so as to bring their interference fringes into coincidence with the back focal point of the objective. Another combination of two birefringent prisms, separated also by a half-wave plate, is placed in front of the condenser. Both these prisms are set so as to bring their own interference fringes into coincidence with the front focal point of the condenser. One of the subcon...

Transfer Function of the Williams Interferometer Used as a Fourier Spectrometer

Abstract: The interferometer consists of a beamsplitter and two spherical mirrors. Each mirror forms an image of the source on the detector. The transfer function is calculated for a point source and various detectors comparable in size to the diffraction images. The path difference is introduced by moving either one or both of the mirrors. For large detectors, the maximum-permitted path difference is twice the focal tolerance. For small detectors, the usable path difference is somewhat larger but depends on the manner in which the path difference is varied.

The Use Of Image Quality Criteria In Designing A Diffraction Limited Large Space Telescope

Abstract: Marechal's criterion for diffraction limited performance, based on a Strehl definition of 0.80, is extended to include the effects of image motion and a central obstruction, as well as wavefront error. The properties of the extended Marechal criterion are studied to show how it can be used to establish tolerable levels of wavefront error and image motion, and the maximum permissible value for the central obstruction diameter ratio. The limitations of Marechal's criterion are examined by comparing it briefly to other image quality criteria. The properties of the Ritchey Chretien telescope are described in a form permitting analysis of its image-forming characteristics. The manner in which the choice of telescope design parameters can influence the amounts of wavefront error and image motion and the size of the central obstruction is described. These properties are then used in conjunction with tolerance levels established using Marechal's criterion to show how an image quality criterion can limit the choice of telescope design parameters. Tentative boundary diagrams are presented indicating the probable range of design parameters that can be used for the large space telescope, based on the use of Marechal's criterion.© (1972) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A Pupil-scan Aberration Analyser

Abstract: The principles of operation of an instrument which can measure the wavefront aberrations, transverse-ray aberrations, and spot diagrams of an optical system are described. The instrument functions by scanning the pupil of the optical system with a ‘ray’ of light and measuring the coordinates of the point of intersection of the ray, with the image plane, using a position-sensitive detector. An image-dissector tube is used as the position-sensitive detector. The instrument also has a facility for generating a polynomial function which can be matched to the measured aberration curves in order to determine directly the aberration coefficients.

Image-plane carrier hologram recording system using spherical wavefronts

Abstract: An image-plane carrier hologram recording apparatus utilizing coherent object and reference light beams having spherical wavefronts is described. In one embodiment, a pair of lenses is employed. One of the lenses images the object beam on a recording plane for interference with the spherical wavefront of the reference beam. The other lens focuses the object beam into a small point of divergence in a plane which also includes the point of divergence of the reference beam to effect cancellation of spherical components at the recording plane. In another embodiment a single lens image-plane hologram recording apparatus is described.

Possibilities of Optical Elements Design Using Phase Holograms

Abstract: Design principles of holographic optical elements are discussed. It is shown that a phase hologram with a high efficiency can be produced that transforms the input wavefront into an output of the required directivity. Such holograms can be used in laser systems instead of complex multilens objectives. Holograms have been obtained experimentally with a diffraction efficiency of 70%.

Hologram Interferometry and Laser Speckle Methods: Further Applications

Abstract: The wavefront reflected from a surface may be stored in a holo gram and subsequently reconstructed to take part in optical interference with any other wavefront. In applications where surface deformation is to be measured, the two wavefronts, although complex, are very similar, and the concept of homologous rays can be used. If two different surfaces are to be compared, however, the wave-fronts scattered from each will in general be too dissimilar in detail to yield an interference pattern showing the mean difference in shape. This difficulty can be overcome to some extent by illuminating the surfaces at a high angle of incidence, when an increasing proportion of the light will be scattered specularly. The nearly smooth waves so generated can then be compared interferometric-ally. The high angle of incidence will of course decrease the sensitivity of measurement.