Showing papers on "Tilt (optics) published in 1974"

Digital Wavefront Measuring Interferometer for Testing Optical Surfaces and Lenses

Abstract: A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

The seven phases of sodium niobate

Abstract: Sodium niobate, NaNbO3, has seven structures belonging to the perovskite family, comprising the aristotype 1 (with the ideal perovskite structure) and six hettotypes 1 (structures with lower symmetry). The differences between them can be systematized in terms of two factors, displacement of Nb from the octahedron centres, and tilting (rotation) of octahedra about the lines joining their centres. These each can be resolved into components, displacement com-potents along the three tetrad axes, and tilt components giving angles of tilt about the same three axes. Displacement components and tilt components are independent in origin but may interact. The phase changes at successive transitions involve the disappearance one by one of tilt or displacement components, until the cubic aristotype is finally reached. At the lower transitions, change of sense of tilt components occurs, leading to large energy barriers. Loss of tilts at the higher transitions is correlated with the occurrence of soft modes. D...

Sandwich hologram interferometry: a new dimension in holographic comparison.

Abstract: New methods are introduced that utilize interferometric comparison of images of diffusely reflecting objects from different hologram plates that are sandwiched together. To make the plate positions optically and mechanically identical during reconstruction and exposure, they are also exposed in sandwiches. If the two sandwiched hologram plates are separated by a small distance a new method of fringe evaluation can be used. Fringes caused by object tilt between two exposures can be eliminated by an analogous, but much larger, tilt of the sandwich hologram during reconstruction. Even the direction of tilt, forward or backward, is found this way.

Lateral table tilt for Caesarean section.

Abstract: The deleterious effects on maternal haemodynamics of inferior vena-caval compression by the gravid uterus are well e~tablished.'-~ The resultant decrease in cardiac output may constitute a threat to both mother' and f ~ e t u s . ~ ~ These problems may be alleviated by lateral displacement of the uterus,'\", by tilting the patient with a wedge,\" or by operating in the left lateral position.'3 Lateral table tilt may be advantageous for Caesarean section using spinal analgesia, but results appear less conclusive under general anaesthesia.'

Noncontact surface profilometer

Abstract: An electrooptical sensor is described for providing an output proportional to the surface profile and the first derivative of the surface profile in a noncontacting manner. A narrow, collimated laser beam is scanned across the surface of the article to be measured. The scanning laser beam is produced with a uniformly rotating mirror and a lens, and the scanning beam is nominally perpendicular to the surface of the article being measured. The laser beam reflected by the surface is collected by a lens and focused onto a photoelectric position sensor. The output of the position sensor is proportional to the first derivative of the article surface profile. Since this first derivative will in general include a component originating from the tilt of the article surface relative to the scanning laser beam, means are provided for separating this effect from the intrinsic surface slope. By electronically integrating the first derivative output, an output representing the surface profile is obtained.

Tilt Precursors before Earthquakes on the San Andreas Fault, California

Abstract: An array of 14 biaxial shallow-borehole tiltmeters (at 1O(-7) radian sensitivity) has been installed along 85 kilometers of the San Andreas fault during the past year. Earthquake-related changes in tilt have been simultaneously observed on up to four independent instruments. At earthquake distances greater than 10 earthquake source dimensions, there are few clear indications of tilt change. For the four instruments with the longest records (> 10 months), 26 earthquakes have occurred since July 1973 with at least one instrument closer than 10 source dimensions and 8 earthquakes with more than one instrument within that distance. Precursors in tilt direction have been observed before more than 10 earthquakes or groups of earthquakes, and no similar effect has yet been seen without the occurrence of an earthquake.

Earth reference thin-film magnetometer compass exhibiting total tilt immunity

Abstract: A thin film compass apparatus utilizing a plurality of thin film magnetometers arranged in an orthogornal coordinate system to provide an earth reference compass having total tilt immunity.

Compound optical system with image tilt compensation

Abstract: An optical arrangement, particularly for ground-based flight simulating apparatus using an optical probe moving over a terrain model to provide a visual display of terrain overflown. The optical arrangement provides a fully in-focus image on a television camera tube target which is inclined relatively to the plane of the terrain model. The optical arrangement may equally be applied to a laser beam scanned terrain model. The arrangement comprises first and second optical systems, usually lenses or lens combinations, and a deflecting means therebetween, usually lens, prism and mirror elements, producing a tilt of the in-focus image plane of the overall system.

Unobscured Aperture Stigmatic Telescopes

Abstract: A large aperture diffraction limited off-axis optical system adaptable to duplexed transmitter and receiver operation has been designed The system employs tilted stigmatic telescopes consisting of paraboloidal primary and secondary mirrors The magnifications and tilts are selected to remove focal plane tilt

Chair structure and tilt mechanism therefor

Abstract: An improved chair structure and tilt mechanism for office chairs and the like wherein the chair back is mounted to the tilt mechanism through the chair arms causing the chair arms to thus move forward and backward in conjunction with like movement of the chair back independently of any movement or tilt of the chair seat.

Ultrahigh‐vacuum manipulator for LEED studies

Abstract: A simple manipulator is described which allows rotation of a target crystal about two mutually perpendicular axes in addition to the normal up‐down, tilt, and translational motions.

Tilt indicator for shipping containers and the like

Abstract: A tilt indicator having two pendulums pivoted on a body whose tilt is to be indicated and limited by ratchet means to rotation in opposite directions and prevented from return rotation so the angular position of each pendulum is an indication of the maximum tilt of the body in its permitted direction of rotation.

The measurement of small phase angles in the subaudio frequency range

Abstract: A method is described which allows for the measurement of small phase angles in the subaudio and audio frequency range. The signal representing the difference of the two primary signals is displayed against either primary on an oscilloscope. This results in an ellipse which may be rotated by changing the amplitude of one of the primaries. When the angle of tilt of the ellipse is zero, the tangent of the phase angle is obtained as the ratio of the minor to the major axis.

Track curvature measuring device - uses a rail van with a unit remaining horizontal independently of body tilt

Abstract: The apparatus is especially for street-cars to measure the curvature of the track. This device can be a gyroscope with an accelerometer mounted on it and over the van axle or a bogie pivot. The outputs of the accelerometer and a speedometer are connected to an analogue computer. The radius of curvature is determined from the square of the velocity divided by the acceleration.

Electronic circuit using charged pins for determining impact planarity in shock wave experiments

Abstract: An electronic circuit using charged pins has been designed to permit the accurate determination of the impact planarity (tilt) in shock wave experiments. The tilt circuit generates voltage pulses with risetimes of approximately 3 nsec. The circuit is described and its operation is discussed.

Tilt moiré patterns

Abstract: Consideration is given to the image formed in the electron microscope of two crystals stacked one above the other when these show a relative rotation about an axis perpendicular to the electron beam. Dark‐field moire fringe patterns are predicted when certain conditions relating to the relative proximity to the Bragg condition of the two crystals are fulfilled. The limits of these conditions and the spacings of the fringes are formulated in terms of the angle of tilt and the direction of the tilt axis.

An investigation of open and closed loop tilt monitors employing electrolytic spirit levels

Abstract: Reports an investigation into the use of a cheap electrolytic spirit level (vial) to detect change of building tilt due to soil subsidence (a few milliradians in a temperature environment of at least -5 to 30 degrees C). Vials of this type were found to have a wide spread in tilt sensitivity (for example +or-25%) and a significant tilt temperature coefficient ( beta ) of about -1% degrees C-1. An open loop tilt monitor requiring calibration with each vial is described; readings can be taken quickly, it has linearity of about +or-2% and employs an oscillator with negative source resistance to reduce beta to -0.1% degrees C-1. In a novel closed loop tilt monitor a vial is mounted on a piezoelectric bimorph and the voltage applied to the bimorph (being the output) is adjusted automatically to bring the vial to a horizontal position; linearity is about +or-0.5%, beta has a value of -0.1% degrees C-1 (without a special oscillator), but the system takes as much as 10 min to settle after large disturbance of the sensing head, which makes it unsuitable for the particular application. Both experimental monitors experience tilt offset of about -10 mu rad degrees C-1.

Tests of an airborne tilt-indicator

Abstract: Distortions of parallax and photographic base caused by tilt introduce significant errors in the photogrammetric determination of tree height. An airborne system to measure and record tilt at the instant of photographic exposure was tested. Longitudinal tilt was measured to an accuracy of plus or minus 0.3 degree 95 percent of the time. It is concluded that, for photogrammetric values typically used in large-scale aerial photography applied in forest inventories, this accuracy is satisfactory.

An improved specimen capsule for the Hitachi HK-5 high resolution tilt stage

Abstract: A specimen capsule has been built which can be inserted into the standard Hitachi HK-5 tilt stage. This capsule allows easy insertion of the specimen into the microscope, smooth tilting and improved stability of the specimen image.