The first known photograph taken by a flash of light from an electrical discharge (spark) was accomplished about 1850 by Henry Fox-Talbot in England shortly after he invented the negative-positive process that is used so widely today. However, electrically produced flashes did not become a commonly used method until quite recently. In this article I discuss some of the exciting developments of the recent past in strobe photography, and relate some of the history that brought about this remarkable revolution in the photographic world.
In the preface to this book, the author states that it is "intended for students who seek a simple intro- duction to the Fourier principles of modern optics and an insight into the similar role they play in other branches of science and engineering." He also states that it is intended as a supplement to "undergraduate mainstream textbooks on optics."
During the past two decades there have been many changes in precision surface metrology. The introduction of the laser and the large computer during the 1960s and 1970s produced many changes in testing capabilities and requirements. Several commercial interferometers became available in the 1970s, enabling people who were not necessarily experts in interferometry to use interferometers to produce better optics. Since both buyers and sellers could test optics, the quality of the optics manufactured and sold improved greatly. If a person ordered 1/10 wave optics, he would probably get 1/10 wave or better optics; if he got optics of lower quality, he would know it, and he could prove it and return it.
A generalized algorithm for use with digital heterodyne or fringe-scanning interferometers was developed that removes many of the restrictions that had previously applied to the data collection scheme. The required phase steps may be chosen with unequal spacing and to extend over a range greater than 27r. The integrating-bucket and phase-step approaches produce identical results.
A lateral-shearing heterodyne Twyman-Green interferometer was constructed to test lenses in transmission. The goal was to determine the repeatability of the measurement of the phase of the wavefront produced by the lens. A second interferometer was used to monitor the phase modulation used in the heterodyne scheme. The wavefront map was computed by a generalized least-squares procedure. Measured phase stabilities were better than 1 mX ( 1 m X = 10-3X, called "milliwave").
A technique for accurately measuring the wavefront aberration of aspherical optical surfaces with a lateral-shearing interferometer is described. A computer-controlled interference phase measuring technique is employed, which provides greater accuracy and real-time data analysis. Key elements of the present system are a lateral-shearing interferometer with a parallel plate, a piezoelectric-driven mirror, an areal image detector, and a microcomputer system with a graphic display. The shearing interferometer gives a fringe pattern corresponding to the derivative of the wavefront, which is analyzed by the fringe scanning method. By integrating the derivative of the analyzed data, we have the wavefront aberration of the test optics over an aperture containing a 32 X32 element array. A rms accuracy of measurement of 1/32 wavelength is achieved on the evaluation of an f/4 aspherical mirror.
Conventional phase measuring interferometry normally requires one-half to sixty seconds acquisition time, limiting measurement to stationary phenomena such as optical element wavefronts. We have developed an instantaneous phase measuring interferometer (PMI) that measures displacements at one point to a resolution of 0.003 um. We describe this instrument and an interferometer measuring phase to X/2000 with a measurement time aperture of less than 1 As. Also described is an attached system for analyzing and displaying wavefronts at up to 10 Hz.
An optical heterodyne profilometer breadboard with surface roughness measurement sensitivity to 0.1 A has been developed and demonstrated. Optical and electronic common-mode rejection techniques were employed in the optical heterodyne precision phase measurement scheme to resolve the optical phase to one part in thirty thousand. Vibration-induced optical phase jitter in the system was nearly eliminated by these common-mode rejection techniques. This noncontact profilometer is capable of characterizing mirror surfaces and is not limited only to flat and/or highly reflective surfaces. Con-cave surfaces, such as the x-ray mirrors for the Advanced X-ray Astrophysical Facility (AXAF), may be characterized as well. Several mirror samples, including two x-ray mirror samples, have been characterized with the optical heterodyne profilometer. Roughness measurement results for the x-ray mirror samples have been compared with those obtained by other methods.
Direct phase measurement interferometry can provide a fast and accurate means of obtaining surface data. Solid-state detector arrays are ideal imaging devices for these instruments. These imagers can be coupled to micro-computers for phase calculation. This article discusses the use of CCD arrays and techniques for digitizing and interfacing these arrays to microcomputers.
A method for the absolute calibration of a flat optical surface is described. An algorithm which utilizes the orthogonal properties of the Zernike polynomials was used on interferometric data to fabricate and certify three 10-inch Zerodur reference flats to X/100 peak-to-valley quality.
A set of functions is presented which is orthonormal over the surface of a cylinder. The functions are useful for describing surface errors on the types of near-cylindrical optics found in x-ray and some extreme ultraviolet systems. In addition, the functions provide a convenient means of using surface deforma-tion data to separate rigid-body motions (misalignments) from surface errors. The functions are sinusoidal in the azimuthal direction and polynomial in the axial direction. In this paper, the functions are detailed in terms of the form of their corresponding surface errors. Also, some general relationships are given, which relate the surface errors defined by these functions to the resulting wavefront errors and focal plane errors. These relationships depend explicitly on the nature of the wavefront incident on the optic. This paves the way for describing the wavefront (either in a metrology configuration or in the real system configuration) in terms of the errors on the optic and the misalignments in the system. A specific example for calculating wavefront and focal plane errors is worked. Finally, some parallels are drawn between the use of these functions for describing near-cylindrical optics and the use of Zernike polyno-mials for describing conventional optics.
A family of three phase measurement techniques are described that are spatial analogs of the popular temporal phase-shift methods. For these spatial techniques, the need for an active element such as a piezoelectric translator or an electro-optic crystal is eliminated simply by adding tilt to the fringe pattern. Measurements are obtained over a uniform grid with an accuracy comparable to temporal phase-shift interferometry. Advantages and disadvantages are discussed.
Interferogram analysis is discussed as a sampling problem using the concepts of Fourier analysis. The relative merits of random, raster, and uniform sampling of a wavefront are examined. A relationship between a global least squares fit and interpolation in the spatial domain and transfer functions in the frequency domain is described.
A high speed automatic flatness analysis system for very large scale integrated circuit wafers has been developed. By using the Fizeau interferometer, a contour map of a silicon wafer is generated, which is then analyzed with a digital image processing system. A special hardware system that performs basic image processing operations, including fringe-peak detection, fringe thinning, fringe-order labeling, local averaging, and so on, was developed. Warpage and undulation of the wafer, which are represented by special indices, are estimated. The surface is not contacted at all during measurement.
The operation of a differential scatterometer developed at Montana State University is briefly described. The scatterometer takes and stores data under computer control. Analysis routines allow calculation of the surface power spectral density (PSD) function for the cases of one-dimensional surfaces [Z(x) - diamond-turned surfaces, for example] and isotropic two-dimensional surfaces [ Z(x,y) - polished surfaces, for example] . In addition, the zero and second moments of the PSD may be taken to provide bandwidth-limited values of the root mean square roughness (cr) and the root mean square slope (m). Results from several samples are used to check the vector perturbation theory [E. L. Church and J. M. Zavada, Appl. Opt. 14, 1788 (1975)] used by the computer to relate the scatter distribution function to the PSD. These experiments take advantage of the fact that the surface - and hence its PSD - remain a constant function during the measurements. Variations in the incident angle and polarization are introduced, and the resulting PSDs are calculated and compared. In another experiment, the min/max scatter angles (or, conversely, the min/max PSD spatial frequencies) are matched to those of a total integrated scatter (TIS) system. Integration over the light scatter data and the PSD allows direct comparison to the TIS and effective rms roughness obtained by the TIS system.
The unified transfer function approach to the design of laser barcode scanner signal acquisition hardware is considered. The treatment of seemingly disparate system areas such as the optical train, the scanning spot, the electrical filter circuits, the effects of noise, and printing errors is presented using linear systems theory. Such important issues as determination of depth of modulation, filter specification, tolerancing of optical components, and optimi-zation of system performance in the presence of noise are discussed. The concept of effective spot size to allow for impact of optical system and analog processing circuitry upon depth of modulation is introduced. Considerations are limited primarily to Gaussian spot profiles, but also apply to more general cases. Attention is paid to realistic bar-code symbol models and to implications with respect to printing tolerances.
In this paper we briefly recall the Floquet theory and show how to apply it to the problem of laser-molecule interaction. In particular, we use the Floquet theory to obtain analytical expressions for the energy shifts in two- and three-level systems induced by the radiation source. This allows the evaluation of the influence of the electric strength on energy shifts in molecular systems.
An optical system was developed to measure the straightness of a slit to better than 0.04 Am peak-to-peak. The slit (part of a reticle pattern) was 19 Am wide and 25 mm long, lying across the center of one face of a convex spherical lens. The system demonstrated a 0.02 Am peak-to-peak measure-ment repeatability, with a capability of achieving higher accuracy.
The signal and noise flow in a parallel thermal imaging system is described. The analytic model used is based on linear system approximation and includes the human observer. The effect of the electronics on the signal-to-noise ratio is discussed, and an optimal response is calculated for sampled and unsampled parallel thermal imaging systems.
The dynamics of a flexible disk rotating near a rigid flat plate are characterized experimentally using a laser Doppler vibrometer. The goal of the investigation was to determine the mechanism by which the gap between the disk and the base plate varies with time. A periodic averaging scheme is used to separate the instantaneous gap signal into a periodic component phased to the rotational position of the disk and an independent random component. The periodic component is shown to dominate, demonstrating that the gap variation is caused by permanent deformations of the disk moving past a fixed point. The base plate stabilizes the disk by flattening the deformations, and the gap variations can be further reduced by increasing disk rotational speed. Disks having 100 and 180 Am thickness were investigated; the thicker disks are shown to have less residual curl. The stabilizing influence of the base plate is lost as the hub height is increased, which implies that hydrodynamic forces are essential to the stabilization mechanism. The mean disk shape is generally a linear function of radius; no self-regulating region was observed.
In this paper we present a calculation of threshold laser writing powers for textured optical storage media. The threshold powers are affected by the optical properties and microstructure of the textured layer, and the thermal conduction from the spot that is machined by the laser beam. Our calculations are compared to experimental values obtained with textured germanium and silicon optical storage media. The results give useful informa-tion about the optimization of the laser writing process.
The origin of enhanced fluctuations in light scattered by very rough surface-like systems is discussed. Both Fresnel and Fraunhofer region effects are considered, and some connection is established between observed features of the intensity pattern and surface type. Statistical models for non-Gaussian scattering are reviewed and their predictions compared with experimental data.
Infrared-transmitting silver halide fibers, 0.3 to 1 .0 mm in diameter, were fabricated by extrusion and were found to have losses of about 1 dB/m at X = 10.6 Am. Infrared heterodyne experiments have been carried out using these fibers. Two stabilized CO2 lasers, of frequencies col and cwt, were used. The two laser beams were coupled into a single infrared fiber, using a Y coupler, with no other optics. Both beams were transmitted through this fiber to a fast IR detector. A heterodyne signal at a beat frequency cal - (02 was obtained from the detector.
Germanate glass (Ge02-Sb203) optical fiber has been drawn from a preform glass rod prepared by the vapor-phase axial deposition (VAD) method. Transmission loss as low as 13 dB/km at the 1.1 Am wavelength has been obtained for a silicone resinclad fiber, and 5 dB/km at 2 Am and 23 dB/km at 2.4 Am have been obtained for a fiber with germanate glass cladding. If a germanate glass fiber of ideal design with a water content as low as 1 ppb (as has already been achieved for high-silica fiber prepared by the VAD method) is prepared, a loss of less than 0.1 dB/km is anticipated around the 2.2 to 2.4 Am wavelength.
The deposition rate in laser chemical vapor deposition (LCVD) is a function of the surface temperature and therefore also a function of the chang-ing reflectivity of the surface during deposition. The influence of these parame-ters on the LCVD rate of metallic and insulating thin films was investigated using both pulsed and cw laser sources and optical monitoring of the depositing film thickness. Physical properties of the LCVD films are reported.
In the drive toward achieving controlled thermonuclear fusion using magnetic confinement of high temperature plasmas, there is a critical need for detailed knowledge of essential plasma parameters such as electron density and temperature. Lasers have made significant contributions to the magnetic confinement fusion program by providing nonperturbing measurements of almost all desired parameters with high spatial and temporal resolution. A wide variety of lasers have been utilized with wavelengths covering the range from the vacuum ultraviolet (-1200 A) to millimeter regions of the spectrum. To illustrate the impact that lasers have made in plasma diagnostics, this paper reviews the selected techniques of laser interferometry, Thomson scattering, and laser resonance fluorescence, together with the relevant laser require-ments. The current state of the art is described, and future needs are projected. The successes already achieved will ensure an expanding role for lasers in the fusion energy program.