Showing papers on "Tilt (optics) published in 1989"

Improved methods of estimating shape from shading using the light source coordinate system

Abstract: This paper develops improved methods of estimating local surface orientation from shading information with the aid of a coordinate system having one axis in the (assumed) direction of the light source. In this system, the surface tilt is related to the direction of the gray level gradient at the given point. An alternative formulation of the surface slant probability density is developed that takes the discrete nature of digital images into account, and that yields a better estimate of the light source direction.

Going on tilt: Frequent poker players and control

Abstract: This paper is based on three years of participant observation in California's legal commercial card parlors and one year observation at an open meeting of Gamblers Anonymous (G.A.). The grounded concept, tilt, is advanced to describe the process of losing control in the gambling situation. Although some problem gamblers and most compulsive gamblers (members of G.A.) did not use this term, they, nonetheless, described the same process. Tilt is defined and broken down into its various components. Paths to, or ways of going on tilt and the means used to avoid tilt are spelt out. Hochschild's concept, emotion work, is used to describe how successful professionals stay off tilt. The major contention of the paper is that all gamblers experience tilt, and their reactions to tilt and to tilt-inducing situations partly determine whether or not gambling becomes a major problem. The implications of tilt are also discussed.

Reflection loss of laser mode from tilted end mirror

Abstract: The reflection of the lowest-order guided TE mode of a slab waveguide from a tilted end mirror is discussed. The problem is applicable to injection lasers if the slab is regarded as an effective refractive index approximation of the channel or ridge waveguide of the laser structure. For a mode width of 3 mu m, 5 degrees mirror tilt results in reflection losses in excess of 25 dB; for modes of 6- mu m width, 5 degrees mirror tilt causes reflection losses in excess of 45 dB. For small tilt angles the results of this calculation agree with those based on a Gaussian approximation of the guided mode. For larger angles, and hence higher reflection losses, the results depart significantly from the Gaussian approximation. >

Theoretical evaluation of the isoplanatic patch of an adaptive optics system working through the atmospheric turbulence

Abstract: Wave-front degradations induced by atmospheric turbulence on optical beams vary with the direction of propagation of these beams. The different compensating methods of turbulence effects are therefore limited to a small field of view called the isoplanatic patch. The dependence on field angle of classical aberrations (tilt, defocus, astigmatism. . .) enables the characterization of the performances of an adaptive optics system working on the concept of pre-compensation. The behaviour of such a system versus the field angle is estimated for different sets of working parameters such as the ratio D/r0 (telescope diameter over the coherence diameter of the turbulence), the wavelength of the detected radiation and the number of eigenmodes on which the correction is made. An adequate choice of these parameters leads to an optimal use of the system with respect to the chosen quality criterion.

On the structural unit model of grain boundary structure

Abstract: A critique of the structural unit model is presented. It is shown that the predictive capacity of the model is severely limited when it is applied to boundaries with relatively-high-index rotation axes. Recent computer simulations suggest that ‘high index’ means 〈221〉 and above. A new approach to grain boundary structure is needed for mixed tilt and twist boundaries.

Optical head with a tilt correction servo mechanism

Abstract: An optical head device includes a tilt servo mechanism using photodetectors for detecting rays of light reflected from the recording surface of an optical disk. The rays of light are obtained from a laser diode used as a light source for information reproduction. According to one aspect; prisms are formed on the flange of a converging lens to refract peripheral portions of the light emitted from the laser diode for tilt detection. According to another aspect, secondary diffraction grating domains at the sides of the primary diffraction domain of a diffraction grating diffract peripheral portions of the emitted rays of light for tilt detection. According to another aspect, a mirror reflects peripheral portions of the emitted rays from the laser diode. According to a further aspect a mirror reflects the light from the laser diode passing through a beam splitter. Each photodetector receiving the light reflected from the recording surface of the disk may be partitioned into two detector cells, and a tilt signal is obtained as the differential output of the two cells.

Multiple feedback effects in asymmetric external cavity semiconductor lasers

Abstract: Multiple feedback effects on the output power and spectral characteristics of an external cavity semiconductor laser with asymmetric feedback induced by misalignment of an external mirror are discussed. The external mirror tilt modifies the round-trip phase condition as well as the coupling efficiency. Undulation in power as a function of external mirror tilt have been observed. At particular tilt angles where strong interaction between odd-order round-trip beams and even-order round-trip beams occurs, unique optical spectra featuring double peaks within a compound-cavity mode spectrum or uneven compound-cavity mode spacings have been observed. A quasi-static model for asymmetric external cavity systems explains qualitatively the power undulations and complex spectral characteristics. The model also predicts the existence of two nearby phase-matched mode groups, which may result in complex and chaotic instabilities. >

Micro-machined accelerometer with tilt compensation

Abstract: A spring-mass-support structure (36') is arranged as an accelerometer with two electrostatic feedback loops so as to measure two components of acceleration. Two of such accelerometers (1010, 1012) are advantageously used on a submerged platform (1006) to determine the direction of a sound source in a body of water. One of such feedback loops (924, 926, 928, 930, 932) of each accelerometer is used to measure low frequency gravitational acceleration applied to the platform as a result of the tilt of the platform due to the action of current and wave action of the water. The other of the feedback loops (124', 126, 150, 164, 166) of each accelerometer measures sound wave induced acceleration on the platform. The gravitational acceleration of each accelerometer is used to compensate the higher frequency acceleration for the effect of tilt of the platform.

Nonlinear behavior of the field-induced molecular tilt near the smectic A-C* transition

Abstract: A deviation from the linear relationship between induced molecular tilt and applied electric field has been observed in the vicinity of the transition from the smectic A to the chiral smectic C* phase. Near the transition temperature Tc, the induced tilt angle θ initially grows linearly with the strength of an applied electric field E, and clearly exhibits a crossover to Eα (1/3 <α<1) above a certain field strength. As temperature increases, however, the exponent α approaches 1 in a wide range of the electric field we studied. A simple mean field model is presented to explain the observed nonlinear behavior.

Tilt and swivel support apparatus

Abstract: Support apparatus for easily and independently adjusting tilt and swivel of a supported product, specifically a visual display device such as a computer monitor. The swivel mechanism permits the display device to be swivelled through a rotational angle greater than 360°, or greater than 180° in each direction from a front reference position. The tilt mechanism utilizes a stack of elongate torsion springs or bars with the stack's mid-portion fixed against longitudinal rotation and with its ends rotatable, including means for providing resistance to such rotation, for counter-balancing the torque produced by the display device in its various tilt positions.

Wavefront detector optimization for laser guided adaptive telescopes

Abstract: Accurate measurement of the wavefront perturbations caused by atmospheric turbulence is vital to the operation of an adaptive optics system. Current systems typically use a Hartmann-Shack wavefront sensor to perform this measurement. This type of sensor uses a lens to translate the problem of phase tilt detection to one of spot centroid detection at the lens focal plane. The accuracy with which a CCD array in the focal plane measures the centroid of this spot is analyzed, taking into account the finite pixel dimension, pixel quantity and dead space between pixels. The optimum design of the wavefront sensor is discussed and the required flux from the reference source is computed. If we require the corrected telescope to have a Strehl ratio of 0.85, and assume typical values for the detector parameters, then the required return flux per seeing cell of size r o is approximately 115 photocounts per measurement.

Diffraction grating for an optical pickup device

Abstract: An optical pickup device for focusing an irradiating ray from a light emitting element on a recording medium and letting a reflected ray reflected from this recording medium focus on a light receiving element is characterized in comprising a diffracting element disposed before the light emitting element and the light receiving element, at least a first diffraction region included in the diffracting element for separating the irradiating ray from the light emitting element into a main beam and sub-beams shifted from the main beam in a direction perpendicular to a track direction of the track where the main beam is focused, a second diffraction region included in the diffracting element for directing a reflected ray of the main beam reflected from the recording medium onto a main light receiving element and directing reflected rays of the sub-beams onto sub-light receiving elements, and an arithmetic circuit for detecting a tilt error signal showing the sub-beam's focusing condition according to the output of the sub-light receiving elements, whereby an optical pickup device does not require installment of any separate tilt sensor for detection of a tilt signal, and also enables prevention of increasing the number of components and the increase of cost as a result of increased assembly steps and/or the required man-hours.

Laser beam path alignment apparatus for laser processing machines

Abstract: To automatically align a laser beam path with respect to an axis along which a movable carriage of a laser processing machine moves, the apparatus of this invention comprises means for detecting laser beam position at least when the carriage is positioned at a first and a second position, means for displaying the detected laser beam positions, and means for adjusting the mirror tilt angle. In the apparatus, the laser beam path is aligned with respect to the axis by actuating the mirror tilt angle adjusting means so that the second laser beam position on the display means is moved to coinside with the first laser beam position. The apparatus of this invention may comprise, instead of the display means, means for calculating an inclination angle of the laser beam with respect to the axis, based on the distance between the first and the second position, and distance between the first and the second laser beam position.

Method and apparatus for beam displacement in a light beam scanner

Abstract: A method and apparatus is provided for line scanning a beam receiving member, wherein a scanning beam is angularly or laterally displaced to compensate for scan line spacing error. The beam is displaced according to error arising from variation (flutter) in the relative motion of the beam and the beam receiving member, or according to error arising from movement of the receiving member while the scanning beam travels to a start of scan position, or both. Embodiments of beam displacement means include a refracting tilt plate, a reflecting tilt plate, a diffracting tilt plate, and a tilt prism.

Short-term variations in strain and surface tilt on Storglaciären, Kebnekaise, Northern Sweden

Abstract: Tiltmeters that can detect changes in slope of a glacier surface as small as 0.1 jJ. rad have been used on Storglaciaren. The records obtained to date have been from the upper part of the ablation area, where the bed of the glacier is overdeepened. A total of 82 d of records has been obtained for various time periods between early June and early September. There is generally a gradual change in inclination of the glacier surface over periods of several days, but these changes do not appear to be systematic. In particular, they are not consistent with vertical movements of stakes located 2-3 ice thicknesses away from the tiltmeters. This suggests that the tiltmeters are sensing disturbances over areas with diameters comparable to the local ice thickness . Superimposed on these trends are diurnal signals suggesting rises and falls of the surface just up-glacier from the riegel that bounds the overdeepening on its downglacier end. These may be due to waves of high water pressure origInating in a crevassed area near the equilibrium line. If this interpretation is correct, the waves apparently move down-glacier at speeds of -20-f)0 m h1 , and become sufficiently focused, either by the bed topography or by conduit constrictions, to result in local uplift of the surface. Also observed are abrupt tilts towards the glacier center line shortly after the beginning of heavy rainstorms. These appear to be due to longitudinal stretching as the part of the glacier below the riegel accelerates faster than that above. Water entering the glacier by way of a series of crevasses over the riegel is believed to be responsible for this differential acceleration. In June 1987, a dramatic event was registered, probably reflecting the initial summer acceleration of the glacier.

Dynamic focussing for recording images from tilted samples in small-spot scanning with a transmission electron microscope.

Abstract: For three-dimensional electron microscopical structure research the specimen must be imaged in a tilted position. Specimen tilt is also often needed to achieve an optimal molecular packing orientation. The tilt with respect to the optical axis causes a defocus gradient alongside the imaged area and thus entails the following complications: 1) The phase-contrast transfer function fades for strong defocus; 2) the Fourier coefficients are split; and 3) the signal-to-noise ratio cannot be enhanced by simple averaging. An image procedure with small-spot scanning and simultaneous defocus compensation is proposed which helps to reduce these problems.

Tilt servo circuit for an optical disc playback device

Abstract: A tilt servo circuit for controlling an optical axis of an optical pickup perpendicularly to the surface of an optical disc such as a Laser Vision Disc or a Compact Disc playbed back by an optical disc playback device comprises a RF level detection circuit for detecting level of an RF reproduced signal from an optical pickup, a tilt changing circuit for changing a tilt angle of the optical pickup, and a tilt servo control circuit for controlling the tilt changing circuit so as to bring the RF level to maximum or substantially maximum. The level of the RF reproduced signal varies with inclination of laser beam with respect to the perpendicular direction to the disc surface, namely the RF level is at the maximum when the inclination is zero and it decreases as the inclination increases. By detecting the RF level and controlling the tilt changing circuit in a manner to bring the RF level to the maximum, the inclination of the optical axis of the laser beam can be corrected.

Amplifier device with coupled surface emitting grating

Abstract: A surface emitting grating is coupled to an optical amplifier and has grating elements tilted non-normal relative to the amplifier optical axis. The angle of tilt in one embodiment is such that the grating reflections are refracted out of the amplifier region. The amplifier may have a tilted light receiving end serving as an input port in a second embodiment to cause internal reflections from the grating to be reflected to an amplifier boundary at an angle greater than the critical angle to cause the reflections to pass out of the amplifier region. In the latter embodiment, the grating tilt angle is minimized to reduce the surface emission beam angle tilt from the normal to a relatively small angle.

Two-axis beam steering system for use in automated light fixtures

Abstract: A beam steering mechanism for deflecting a light beam along any selected azimuth and elevational direction. The beam is movable without limitation about a pan axis (42) and about a tilt axis (48), by drive motors that are rigidly mounted to a housing (10) and are not bodily moved with the light beam. Movement about the pan axis (42) is effected by rotation of a first mirror (50) mounted in a first rotatable cylinder (40). Movement about the tilt axis (48) is effected by rotation of a second mirror (52) mounted in a second cylinder (46) that is panned with the first cylinder (40) and is itself mounted for rotation about the tilt axis (48).

Two-dimensional tilt illusions induced by orthogonal plaid patterns: effects of plaid motion, orientation, spatial separation, and spatial frequency.

Abstract: Tilt illusions occur when a drifting vertical test grating is surrounded by a drifting plaid pattern composed of orthogonal moving gratings. The angular function of this illusion was measured as the plaid orientation (and therefore its drift direction) varied over a 180 degrees range. This was done when the test and inducing stimuli abutted and had the same spatial frequency, and when the test and inducing stimuli either differed in frequency by an octave, or were spatially separated by a 2 deg blank annulus, or both differed in frequency and were also separated by the annulus (experiments 1-4). The obtained angular function was virtually identical to that obtained previously with the rod and frame effect and other cases involving orthogonal inducing components, with evidence for illusions induced both by real-line components and by virtual axes of symmetry. Although the magnitude of the illusion was very similar in all four experiments, there was evidence to suggest that largest real-line effects occurred in the abutting same-frequency condition, with a pattern of results similar to that obtained previously with the simple one-dimensional tilt illusion. On the other hand, virtual-axis effects were more prominent with gaps between test and inducing stimuli. A fifth, repeated-measures, experiment confirmed this pattern of results. It is suggested that this pattern-induced tilt effect reflects both striate and extrastriate mechanisms and that the apparent influence of spatially distal virtual axes of symmetry upon perceived orientation implies the existence of AND-gate mechanisms, or conjunction detectors, in the orientation domain.

Tomographic reconstruction from energy-filtered images of thick biological sections.

Abstract: Energy filtration makes it possible to image an approximately 0.5 microm biological section at 80 kV in the electron microscope. Based on spectra taken at different tilt angles, we chose the most probable energy loss, deltaEp +/- 10eV for each tilt angle, as the imaging energy window. A complete tilt series from +60 degrees to -60 degrees at 2.5 degree intervals was collected on the Zeiss EM902 and used in a tomographic reconstruction of transcriptionally active chromatin in the Balbiani ring of Chironomus tentans.

Shade screen for the windows of motor vehicles

Abstract: A window shade screen is disclosed in combination with the window of a motor vehicle. The screen includes horizontal slats and a tilt plate positioned thereabove. An assembly for associating the tilt plate with the slats is provided, so that tilting of the tilt plate tilts the slats concomitantly therewith. An assembly is also provided for removably securing the tilt plate to the window, so that the screen moves upwardly and downwardly with the window. An assembly is further provided for securing the slats to the tilt plate. Finally, a chamber is provided for receiving all the components of the screen when the screen is not in use.

On the average misorientation angle of general tilt boundaries

Abstract: On the basis of a simple geometrical analysis, exact formulae for the average misorientation angle of random tilt boundaries in the structural unit and disclination models are obtained. Two important consequences following from these formulae are considered: the relation between the Burgers vector of grain boundary dislocations and the geometrical parameters of short-period areas composing the random boundary, and an exact expression for the Burgers vector of a dislocation equivalent to a disclination dipole with given strength and structure of the related boundary

New Method Of Contouring Using Digital Speckle Pattern Interferometry (DSPI)

Abstract: A new method of contouring 3-D objects in real-time is suggested. The technique makes use of Digital Speckle Pattern Interferometry (DSPI) alongwith an in-plane sensitive optical configuration. The contour interval can be varied in real-time by varying the tilt applied to the object. The variation of the contour interval with the tilt angle and the angle between the illumination beams is discussed. The decorrelation of speckle pattern due to tilt and consequently the disappearance of the fringes is also discussed. Experimental results have been presented for a variety of objects.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Venetian blind structure

Abstract: A venetian blind structure using a slat unit having first and second members adjacent one another The edge portions of the first and second members are hingedly attached to one another First and second lines are held to the edge portions of the slat unit and are used to tilt the slat when a first and second line are simultaneously pulled in opposite directions

Cone beam SPECT reconstruction with camera tilt.

Abstract: The authors modified the cone beam filtered backprojection algorithm of L.A. Feldkamp et al. (1984) and applied it to the symmetric tilt-angle case. Both the modifications of the algorithm and a single preliminary test are reported.