Jay M. Eastman

A New Optical Surface Microprofiling Instrument

An optical surface microprofiling instrument is described in this paper. The instrument is an interferometric device capable of measuring the the microtopography of a precision surface along a single scan line. A 25 millimeter. scan can be accomplished in less than one minute with the present hardware. The vertical resolution of the instrument is on the order of 10 Angstrons. The lateral resolution is diffraction limited and corresponds to a few micrometers. Surface profile data are output in the form of analog voltages that can be readily digitized by a computer for further analysis, if necessary. The microprofiler is a compact unit that requires no elaborate vibration isolation. Since the test is non-contacting in nature it is a non-destructive test. The instrument can potentially generate surface profile data for large samples. Numerous techniques exist for measuring the microtopography of precision surfaces. A brief overview will highlight the characteristics of the commonly used methods. This discussion will set a background against which the performance of the surface microprofiling instrument can be compared. Examples of surface profile data produced by the instrument for a variety of samples will be presented.

The Scanning Fizeau Interferometer: An Automated Instrument For Characterizing Optical Surfaces

Recently there has been increased interest in the measurement of the microtopography of optical surfaces. The information generated may be used either to predict the scattering characterisitics of a particular surface or to relate surface quality to damage thresholds. Previously, surface profiles have been measured by a variety of techniques including electro-mechanical profilometry and multiple beam interferometry. Surface profiles may also be measured using a scanning Fizeau interferometer. The instrument is similar to conventional Fizeau interferometers, with the exception that the interference pattern is temporally modulated by vibrating the test sample. A detector scanned across the modulated interference pattern produces an ac signal, with a phase that is directly proportional to the profile of the surface under test. An instrument based on this principle has been constructed and is capable of generating profiles of surfaces with rms roughnesses of approximately 20 A. The advantages and limitations of the instrument are discussed. Experimental results are presented.

Microprofiling Of Precision Surfaces

A long scan non-contacting optical surface microprofiling instrument is described in this paper. The instrument l, based on the principle of differential interference microscopy, measures the profile of a precision surface along a single scan line. The present hardware allows scan lengths of up to 100 millimeters. Data is acquired at a rate of 2 millimeters per second. Calculation of the surface profile from the raw data requires 2 minutes using a standard IBM-PC. The lateral resoluition of the instrument is diffraction limited at 2 micrometers. This paper presents surface profile data for several types of pecision surfaces. Data from a commercial quality optical flat demonstrates vertical resolution of less than 2.0 Angstroms and lateral resolution of approximately 2.0 micrometers. An aluminized surface relief zone plate with vertical surface deviations in the range of 12,000 Angstroms is profiled over a scan length of 3 millimeters. Irregularities approximately 100 Angstroms high are clearly resolved. A scan of a Gaussian diffuser shows the ability of the instrument to profile surfaces with large surface deviations. The RMS roughness of the diffuser is 2.0 micrometers. Data is also presented for a non-optical surface. Surface profile data for a burnished Winchester disk illustrates the use of the instrument to study the surface characteristics of components use for high density information storage.

Diffraction analysis of beams for barcode scanning

Laser based bar code scanners utilize large f/# beams to attain a large depth of focus. The intensity cross-section of the laser beam is generally not uniform but is frequently approximated by a Gaussian intensity profile. In the case of laser diodes the beam cross-section is a two dimensional distribution. It is well known that the focusing properties of large f/# Gaussian beams differ from the predictions of ray tracing techniques. Consequently analytic modeling of laser based bar code scanning systems requires techniques based on diffraction rather than on ray tracing in order to obtain agreement between theory and practice. The line spread function of the focused laser beam is generally the parameter of interest due to the one-dimensional nature of the bar code symbol. Some bar code scanners utilize an anamorphic optical system to produce a beam that that maintains an elliptical cross-section over an extended depth of focus. This elliptical beam shape is used to average over voids and other printing defects that occur in real world symbols. Since the scanner must operate over the maximum possible depth of field the beam emergent from the scanner must be analyzed in both its near field and far field regions in order to properly model the performance of the scanner.

Optical engineering and the Optical Society of America.

The role of the Optical Society of America in the changing field of optical engineering is discussed by the vice-chairman of the Technical Council of OSA in an introduction to a group of papers that constitutes a representative sampling of optical engineering in the early Eighties.

Polarizing Optical Components For High Power Glass Laser Systems

Large glass laser systems used in laser fusion research operate with intrasystem power densities of up to 1010 W/cm2. These multibeam laser systems utilize numerous subassemblies to perform various tasks. Polarization components are important elements in subassemblies such as unidirectional optical isolators, bidirectional optical isolators and variable ratio beam dividers. At power densities of gigawatts/cm2, nonlinear effects limit the power level that can be prieagatV through a glass laser system. An intensity induced refractive index change of PPM at levels of 1010 w/cm2 can cause whole beam self-focusing and small scale beam break-up. Polarization components for use in these systems must be selected on the basis of minimal contribution to nonlinear phenomena as well as acceptable optical performance. Nonlinear considerations exclude the use of such components as birefringent crystal polarizers and the MacNeille polarizer in the presence of gigawatt/cm power densities. Thin film plate polarizers are used in large aperture low contrast applications because they combine acceptable optical performance with a relatively low nonlinear contribution. This review paper describes some commonly used polarization components and discusses their applicability to high power glass laser systems.

Guest Editorial Optical Fabrication and Testing

Optical fabrication and testing in the United States have been significantly brought together by a series of Optical Fabrication and Testing Workshops in the 1974-1977 time frame. This issue of Optical Engineering features optical fabrication and is intended to be another step in the process of bringing the optical fabrication community together. Our goal is to begin to overcome the natural tendency of the industry to withhold details regarding fundamental principles and important techniques. It is our opinion that the optics industry in the United States would benefit if this policy were universally accepted.