Various instruments to measure the refractive state of the eye have been built based on a servosystem concept. This paper describes the optical system of the Dioptron® automatic objective refractor. This auto-refractor measures the modulation of a grating image formed on the retina while being controlled by a digital computer. The optical subsystems include the image projecting system, the image detecting system, the patient fixation target, and the patient alignment system. Accuracy is obtained by controlling the patient's accommodation and eliminating "instrument" myopia. The overall system is designed to be compact while maintaining very good signal to noise ratio and minimum operator controls.
A holographic camera with motorized x,y,z patient positioner has been constructed and used to estimate tensile strength of corneal wounds in patients who had previously under-gone corneal transplantation. The technique using a krypton ion laser gives high contrast fringes which readily localize to regions of the wound and suture sites, revealing weak or partially healed areas. This will hopefully serve to indicate when the sutures can safely be removed. Intraocular pressure stressing is supplied by the patient every time his heart beats. Double exposure holography is synchronized to occur when the pulse of blood reaches the eye. Thus, no external stress need be applied to the eye; and, since the retinal light exposure is typically 1/10,000th of that received during a conventional fundus photograph, the technique is truly non-invasive. The illuminating system consists of a large hemispherical reflector imaging a diffusely reflecting disk onto the cornea. An expanded laser beam illuminates the disk which is thereby specularly reflected by the cornea into the holographic imaging lens.1Rigid body movement of the eye due to microsaccades occurring between exposures have produced bothersome artifacts. A dual reference beam technique for fringe control has partially overcome this.
Viruses are too small to resolve in an optical microscope so their sizes have generally been measured using electron microscopes. The problem we have addressed is this: there is a solution containing on the order of 1012 viruses per ml. They are all the same size; somewhere between 200A and 3000A in diameter. How does one accurately measure their size using only an optical microscope to view them? The problem is compounded by the fact that even using a focused 100 mwatt laser beam, the amount of light scattered by a small virus is too small to conveniently detect. A further complication: virus-sized particles, in the solutions in which they naturally occur and in which we would like to observe them, are in constant Brownian motion. Our solution to this problem has been embodied in an instru-ment called a Virometer and involves evanescent waves, noise spectra, and fluorescent stains. This paper describes the design and operation of the Virometer, and gives examples of its use. Using a 1 μl sample and a 60 sec observation time, viruses less than 300A in diameter have been accurately sized at concentrations as low as 108 viruses per ml.
Aligning a pulsed CO2 laser fusion system involves control systems which insure that the centers of beams follow a prescribed path to within 1 mm, that the pointing of the beams is correct to ~ 20 microradians, and that focal spot at the location of the experimental fusion target be placed to accuracies of 10-20 micrometers laterally and ~ 50 micrometers axially. These alignments are accomplished by a variety of sensing techniques which include thermal pinholes and quadrant detectors, Seebeck effect silicon detectors, and imaging autocollimating Hartmann test procedures employing it vidicon systems.
An electronic/optical system capable of determining the linear and/or non-linear phase distribution of a complex amplitude wavefront is described. The use of this scheme in space variant pattern recognition is emphasized and its applicability to other optical data processing cases noted.
Techniques for resolving small transverse distances are compared with those for resolving small longitudinal displacements. As the desired resolution becomes finer, there comes a point where both problems are best solved by switching to the transform domain. Techniques for measuring displacement can be divided into those used for nonoscillatory vs oscillatory motions. Examples are described for achieving λ/105 for the former and λ/109 for the latter. Fundamental limitations are discussed.
Holographic optical elements (photographically produced Fresnel zone plates) can be easily designed with lens design computer codes using an analogous lens model. From a ray tracing point of view this lens model focuses light exactly the same as a holographic optical element. The analog works for on-axis rays, off-axis rays and any wavelength.
Laser beam deflection can be obtained by using holographic gratings. For example, a constant-frequency grating rotating normal to the laser beam can scan the laser beam along an arc of a circle. Or, by moving an off-axis zone plate across the laser beam, the linear variation in the spatial frequencies of the zone plate will produce a raster scan line. Even more complicated scanned patterns can be obtained by making the proper computer-generated holograms. In this paper the principle of holographic grating scanner and the consider-ations in making computer-generated holograms to produce beam deflections in two directions will be discussed. Some experimental results will be shown.
This paper describes two methods that add a multicolor property to the rainbow holographic technique. The first method simply superposes three rainbow holograms, each of which is recorded in a different wavelength. It generates a three-dimensional, natural-color image in white light. The second method is also a super-position of rainbow holograms but requires only one wavelength in the entire recording process. The variation of the reference beam angle is converted into different colors. The reconstructed image does not necessarily have the original color distribution; rather it gives us a freedom to encode each exposure in any desirable color.
Under contract to the Lawrence Livermore Laboratory, we have designed and fabricated a new aberration generator for use in a 1-gigawatt, 4-cm-diameter, 1.06-μm laser beam. Four glass lenses, one of which is aspheric, form a unit-magnification, nonachromatic telescope. The elements are shaped and oriented to resist laser damage. Through selected tilt, translation, and decentration of the elements, up to three waves of fourth order and more than 10 waves of second order aberrations can be generated separately or in combination.
When three-dimensional measurements of an object are to be made, two techniques are commonly used : a) If the object itself is available throughout the duration of the measurements, a mechanical finger, which is moved over the object, can be used. The measurements are made by recording the coordinates given by the finger as it is displaced. These measurements thus require a physical contact with the object. This contact may be destructive. b) In cases where no contact with the object can be tolerated, and where the object itself cannot be immobillized, techniques of short-distance photogrammetry can be used. However, this method also presents inconveniences : . certain object forms are not easily photographed from two different angles. . it is difficult to produce stereoscopic plates of objects moving at high translation velocities in normal lighting. . phase phenomena cannot be photographed. Because we are concerned in a large proportion of our activities with the testing of materials and photogrametric interpretation, and are moreover actively involved in the field of research on applications of holography, we have naturally become interested in the possibilities offered by holography in the field of three-dimensional measurement. Holography is, in effect, a technique permitting the recording and reconstruction, in simple fashion, of the image of a three-dimensional object. If certain precautions are taken, a stigmatic image, life-sized, is reconstructed, and we thus obtain, by means of a very simple setup, the equivalent of the " stereomodel " given by the conventional processes of photogrammetry. The exploitation of the image can be made by means of the two distinct techniques which have been studied.
A new method-of generating aspheric elements is discussed. In this method, the aspheric element is produced by sputtering a non-uniform, but radially symmetric. coatino onto the substrate. The desired non-uniformity is produced by selective masking of the substrate. As proof of the concept, an 8.25-inch diameter aspheric element was made. This asphere has a maximum departure from spherical of 84pm and a maximum slope deviation from spherical of 132µm/in. The finished sputtered asphere departed from the design asphere by 0.38µm.
There are many situations in which photographic recordings of imaged data are made under less than ideal conditions. In aerial reconnaissance, ground surveillance, x-ray examinations, and other applications where "retakes" are either undesirable or impossible it is inevitable that some information will have to be extracted from images which are of low contrast due to under or over exposure or to intervening obstructions such as fog, haze, or soft body tissue. This paper will disuss the IDES, which has been designed to increase the intelligence a trained observer may extract from the available images. IDES combines a high quality variable-magnification binocular microscope with the Itek PROM (Pockel's Readout Optical Modulator) to allow an operator to adjust the contrast of the input imagery by changing the image bias while it is being viewed. This contrast adjustment varies continuously from positive to negative, with the intermediate settings resulting in dark contours of constant input intensity appearing in the image. These contours enhance the gradients which form the edges of image details thus making them more visible.
The VISSR fiber optics assembly is a ring-shaped structure, attached to the radiometer aft optics support plate. Main components include a circular mounting ring, ten optical fibers, a right-angle prism, a flexible bellows, and eight filter blocks. In operation, light enters the prism and is bent to fall incident on the fiber ends. Fibers are routed from the common prism through the bellows into individual channels machined into the ring. Eight fibers serve as guides to carry light from the focal plane to detectors positioned symmetrically on the perimeter of the ring. At the prime focal plane they are bonded together in a linear array. The remaining two "end fibers" are used for alignment. Prism movement is used to compensate for thermally induced focus variations. The eight active fibers terminate into optical filter blocks which define the spectral cut-on wavelength.
The LIR instrument has been developed for the RASA Ames Research Center for use in the 1978 Venus Atmo spheric Probe Mission. The mission objectives are to determine the nature and composition of the clouds, the composition and structure of the atmosphere, and the atmospheric circulation pattern of the planet Venus. The The Large Probe Infrared Radiometer (LIR) is a six-channel (3 to 50 µm) internally calibrated radiometer which measures the radiance difference at ±450 to the horizontal as viewed through a single diamond window in the spacecraft. The LIR optical system consists of a unique arrangement of hollow light pipes which optically couple a six element detector/filter array to the spacecraft window while mechanically and thermally isolating the array from the window's harsh thermal environment. A single rotating section with a 45' bend and containing a collimator alternately views up and down through director/extender pipes located adjccent to the diamond window. Light is transferred from the rotating section to a fixed section containing a diamond diffuser to scramble the light. This minimizes asymmetries and improves channel field of view overlap.
There is increasing interest in non-contacting sensors to perform dynamic, in-process gauging to achieve closed-loop adaptive control of manufacturing processes. After a brief review of current instrumentation, a detailed description will be given of those engineering principles and design features which must be considered to achieve stable, reliable measurements with an optical sensor using a scanning laser beam. Several applications will also be discussed.
We have built a modified Twyman-Green interferometer illuminated with a krypton laser. The configuration allows for center of curvature or autocollimation testing at various selected wavelengths. Software data reduction uses a Zernike polynomial fit to the wavefront. The interferograms are all made without moving the source, so the effects of axial color, lateral color, and chromatic variation of aberrations will exhibit themselves in a straightforward fashion in terms of the coefficients of the Zernike polynomials. Also, a scheme for using this information in the calculation of a polychromatic optical transfer function (OTF) has been developed. Requirements for the interferometer's optics are examined, and interferometer calibration discussed.
An air-bearing microinterferometer transducer is being developed to provide for increased accuracy, range, and linearity over conventional linear variable differential transformer (LVDT) transducers. The conventional LVDT's are used on multiple-probe sweep gauges to measure deviation from true surfaces to revolution. These LVDT transducers are null devices, and their high accuracy deteriorates rapidly as they move from zero setting. It is desirable to have a transducer with extended range to measure parts that deviate from conventional paths. The length-measuring interferometer is a well-established inspection device. However, constructing a microinterferometer that will fit inside a conventional 1/2-inch-OD transducer housing is a formidable task. Departure from the conventional interferometer construction is required. It will be necessary to transmit the laser beam into the microinterferometer with a self-focusing fiber optic cable. Miniature glassware has been obtained and a microinterferometer constructed inside an 0.315-inch-ID transducer. Fringes have been obtained by directing a laser beam into the transducer housing.
Inspecting hypodermic syringe needle points has, until recently, been an error prone, time consuming visual process. At a rate of several per second, the human inspector employing a single lens magnifier can easily miss marginal defects or even major defects if a blink occurs at the wrong time. A system that analyses diffraction from the needle tip using a solid state phOtodetector array has been developed. This system inspects up to twelve (12) needles per second with lower error rates than the human inspe ctor. In this paper, we discuss the major elements of the Needle Point Inspection Device. The optical configuration as well as materials handling and control software are described to illustrate the problems involved in bring-ing coherent electro-optical technology into the factory.
A polarizing microscope has been altered to allow optical spatial filtering to be accomplished. The alterations permit a spatial filter to be placed near the back focal plane of the microscope objective and a laser is used as a light source. The instrument can be used to focus on a specimen as would be done for any ordinary application of the microscope, or the standard Amici-Bertrand lens can be used to focus on the Fourier transform of the specimen. For a low power objective, the field of view of the specimen is about one centimeter and the spatial frequency passband is about one hundred lines/mm. The image of the specimen, its Fourier transform, the filtered transform, and the filtered image can each be viewed or photographed using this simple instrument.
A high sensitivity camera and imaging system are employed in a special purpose flow cytofluorometer for extraction of fluorescence images of cells and objects in flow. Each image is uniquely correlated with a fluorescence profile or "slit-scan" contour of the cell also derived in flow. Contours are computer analyzed to extract low resolution morphologic information. Optical considerations for imaging in flow and results obtained from the imaging system are presented.
This paper describes an unequal-path interferometer that requires only one precision component and that can be constructed as a compact and inexpensive instrument. Principles of operation are outlined, and requirements for optical components and alignment are investigated. An actual instrument and considerations for its design are described.
A general image processing facility was developed for the chief purpose of analyzing fringe patterns in interferograms. A video image digitizer was connected to a programmable calculator and in turn to an RS232 EIA communications interface. An interactive software package was developed to control the digitizer and communications interface by means of the calculator keyboard. A semi-automatic procedure for locating the positions of fringes was developed. The fringe data are automatically formated and sent to a larger computer over telephone lines for additional processing.
A technique is described which will convert in real time the irradiance pattern resulting from two interferometry beams into phase information. The interferometer is modified to introduce a known temporal phase modulation to one beam and then to detect minima in the A.C. signal. Three instruments built on this principle will be discussed. The instruments are capable of detecting phase differences approaching λ/100 and may be used for measuring optical interference (roughness, irregularity) or transparent plase objects such as biological samples, microballoons and gradient index materials.