On June 30 of this year I will have served as Editor of Optical Engineering for three years, and, as you might have gathered from the title of this editorial, I have agreed to stay on for two more years-until June 30, 1990. I have decided to step down and let someone else take over at that time and have so informed the Chair of the Publications Committee, Hank Carter.
At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beamlines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the National Synchrotron Light Source) and the effects of these figure errors on two classes of soft x-ray beamlines are presented.
A general method for the analysis of frequency-modulation reticles is presented. The formulation starts by introducing the spoke function f(p) as an offsetting factor to the phase angle 0. Through the process of coordinate transformation, the output signal after demodulation is obtained. The result contains two main parts: the first part represents the contribution from the basic configuration of a straight-edge spoke; the second part, containing the term df/dp, represents the modifying effect of changing the spoke edge to an arbitrary curve. By means of four examples, the method is shown to be valid in verifying the dependence of the output signal on the spoke shape. Any frequency-modulation reticle can be analyzed by this general method so long as its corresponding spoke function is known.
Two models for the analysis of the parameters essential for the design of a frequency-modulation reticle are introduced. One is the point model, which is suitable for estimating the center frequency and the frequency bandwidth. The other is the spot model, which is suitable for calculating the degree of contrast. Using the analytical results derived from these two models, examples are discussed showing the process of reticle design, e.g., determination of the total number of spokes and design of a modification zone by means of a graphical method.
A proposed method for spatially modulating a laser beam involves changing the refractive index uniformly over a variable area. The width of the area pattern is determined by the applied signal to be processed. The refractive index change would be "written" by optical means on the surface of the material. This paper describes the method mathematically and points out key factors that influence recording quality.
A procedure to reconstruct sampled complex-valued objects from
intensity data at the output of a general optical system is given. It is shown that
both the choice of the sampling points at the output plane (uniform or nonuniform
sampling) and the specific values of the intensity at these points determine
the uniqueness features of the reconstruction problem.
Optical serial sectioning is a technique by which the 3-D structure of a microscopic specimen is observed by incrementing the plane of focus of a light microscope through the specimen. Ideally, if the depth of field of the microscope is sufficiently shallow, the image at each focusing plane is an in-focus rendition of the specimen containing structural information from that plane only. Unfortunately, the limited aperture of any practical light microscope makes this unfeasible; at each focusing plane, the 2-D image obtained contains unfocused information from planes above and below the focusing plane. In this paper, the nature of the distortion of the light microscope is analyzed using principles of geometric optics, where it is assumed that the absorption of the specimen is linear and nondiffractive. It is found that the limited aperture of the microscope results in the loss of a biconic region of frequencies in the Fourier spectrum of the specimen along the optical axis, resulting in a severe loss of resolution along the axis; outside the missing cone of frequencies, the spectrum is distorted by a strong low-pass effect, further reducing the resolution of the image observed at each plane of focus.
An optical/digital approach to the classification of small quasicircular grains is described. The setup consists of a coherent optical system to generate the Fourier irradiance of a random scene and a digital computer to process data. The sampling of Fourier spectra is achieved with a wedge ring detector. The inversion formula technique is used to estimate the particle distribution. A scene of three classes of varying sizes of Fe203, FeO rock grains is analyzed, and experimental results are given.
An experiment has been carried out to show that extrinsic silicon injection-mode infrared detectors can be used to simulate the transient response of neurons in biological vision systems. The neural response provides a means of high pass filtering in vision system focal plane parallel processing. The high pass filtering emphasizes transients in images. Possible IR imaging applications include surveillance, motion sensing, and tracking. The IR detector output pulses are sufficiently large that amplification is not required. This could facilitate parallel processing in or near the focal plane. The IR transient sensing approach is quantitatively analyzed in terms of a model for the detector and the associated circuitry. Excellent agreement is found between the model and the experimental data.
Artificial intelligence problems are solved on electronic computers by techniques that make heavy use of address calculation and dynamic management of data storage space. Optical computing, on the other hand, is normally associated with numerical problems in which the size of the data space is fixed and addressing may be handled in a predictable manner not affected by actual data values. In this paper we categorize expert system problems by the amount of dynamic storage management required and discuss several methods for eliminating unnecessary address manipulation by careful choice of data representation. Major emphasis is placed on the implementation of the mathematical technique of resolution. Various resolution strategies are analyzed, and the effect of these strategies on storage management is assessed with a view to minimizing the complexity of processing. Finally, electro-optical implementations are considered for the major functional elements of an optical resolution system.
The basic properties of the surface photodeposition effect are described. The process can be used as an imaging and optical recording method realizable with various light sources such as laser, discharge, or even conventional incandescent white light sources. Since the photo-process is controlled by the dose of light delivered to the photosystem, films of required thicknesses can be obtained in the range 50 to 2000 nm. This makes possible the preparation of various optical devices such as coatings, filters, phase retardation plates, holograms, gratings, and optical patterns for recording data. The optical resolution and contrast were tested by projection and mask contact methods. With both methods, the recorded linewidth resolution of the imaged patterns was about 1000 nm. This figure, however, was the basic resolution of the optical projection system or that of the original mask used for imaging. Theoretical arguments lead us to assume that the effect can provide better resolution due to its special feature of a one-step photographic process involving adsorption on a flat surface without a scattering emulsion on it.
The third-order Seidel aberrations of a four-spherical-mirror system for an anastigmatic aplanat, flat field aplanat, and zero distortion aplanat are analytically derived and numerically investigated, and their residual finite ray aberrations are examined. The anastigmatic aplanat is composed of a front Cassegrainian system and a rear inverse Cassegrainian system, where the image formed by the front Cassegrainian system is relayed by the rear inverse Cassegrainian system. The flat field aplanat is similar in appearance to the anastigmatic aplanat except that the rear part is far larger than the front part. The zero distortion aplanat is composed of a front Gregorian system and a rear inverse Cassegrainian system.
A high resolution noncontact optical sensor for surface roughness has been developed. The principle of the sensor is based on astigmatic focus error detection, which has been employed in the pickup of optical disk players. First, the measuring principle of the method and the optical system arrangement are described in detail. Then, the results obtained by this method are compared with those obtained by the precise diamond stylus method on several different types of surfaces. The light source of the newly developed apparatus is a diode laser with an output power of 2 mW and a wavelength of 790 nm. The objective lens of the sensor is a standard microscope objective, interchangeable with other objectives. The sensor is small enough for on-machine use and has shown sensitivities on the order of nanometers on diamond-turned metal mirrors. It also permits on-machine measurement of surface profiles in cases in which the object surface is mounted on a machine tool.
We have fabricated a thin-film optical detector for detecting short optical pulses propagating in channel waveguides. The detectors show response times of 200 ps full width at half maximum amplitude when illuminated by guided, subpicosecond optical pulses. The detectors are formed by depositing hydrogenated amorphous silicon (a-Si:H) directly on the dielectric channel waveguides. Back-to-back Schottky photodiodes are then formed when interdigitated chrome-gold metal contacts are deposited on the a-Si:H.