It was just a year ago that SPIE published its Proceedings, Volume 53, on Laser Recording and Information Handling, documenting a comprehensive seminar which we are proud to have organized and chaired. Now this special issue of Optical Engineering, highlighting the same subject, has inspired the creation of a new group of excellent papers to express substantial advances in our understanding and application of this growing technology. The series begins with a unique compilation of surveys and study data, representing the considerations of several of our prominent specialists in the field. It concludes with some new applications data, taking advantage of the spectral characteristics of laser radiation in direct color image recording and instrumentation. Two Short Communications - on the distinguishable gray level in high-resolution film, and on semiconductor injection lasers -complete our report.

There is a great diversity of types of lasers and hundreds of possible lasing wavelengths available to optical systems designers today. Laser requirements for recording and information handling often call for specific wavelengths, power levels, and other physical and optical characteristics. This paper presents an overview of four major types of gas lasers suitable for these applications and a comparison of the performance characteristics of each. The review covers He-Ne lasers, He-Cd metal vapor lasers, and argon and krypton ion lasers. The characteristics of the individual laser types include output power level, wavelength output stability, optical noise, input power, cooling requirements and operational reliability.

In recent years, lasers have been used increasingly in applications involving writing and recording on film or other materials. Although most of the applications involve low-power helium-neon lasers, which produce a few milliwatts in the red (6328A), many, particularly those involving newspaper plate-making and video-disk recording, utilize argon-ion lasers, which produce up to 20 watts in the blue-green spectrum and several watts in the ultraviolet.

In order to obtain an optimum design for a laser scan lens, the unique operating characteristics of this type of system must be taken into consideration. This paper discusses various system parameters as they pertain to the design and performance of laser scan lenses. Formulae are given which define the spot size for various conditions of pupil illumination. A figure of merit is provided based on the number of resolvable spots/scan length and is shown to be proportional to scan angle and pupil aperture. Fundamental lens system,configurations based on thin lens approximations are presented and various possible solutions explored. This is followed by specific examples of scan lens designs.

The design of many optical systems presents the problem that the orientation of an optical path of relatively large aperture must be changed rapidly and accurately. When its speed is acceptable, the servo-actuated moving-iron galvanometer has proven to be an economical solution to this prob lem. This paper presents a discussion of the accuracy with which this device can provide beam deflection, with particular reference to linearity, repeatability, hysteresis and temperature drift errors.

Optical data storage systems employing large varieties of different recording materials have been investigated in great detail over the last few years. In this paper, we present a review of most of the known classes of optical recording media and describe a procedure for identifying materials with potential interest for specific applications. To provide a context for demonstrating this point, we pick as an example an optical disc recording and playback system. We feel the most useful application of this type of analysis is to help eliminate those materials from consideration which are unlikely to meet system requirements.

The current trend in high density data storage is toward increased utilization of digital recording and processing techniques. In support of this trend, a review is made of the relative capabilities of optical and magnetic methods. Present technology and future capabilities are appraised on the basis of fundamental considerations dealing with both discrete and composite recordings, area and volume data packing densities, noise and error rates, spatial wavelengths and bandwidths, and data permanence. The two recording methods competitively overlap in very few areas, but do demonstrate separate distinct advantages in specific applications.

The development of the laser recorder is briefly described. The recent availability of non-R&D model laser recorders has made it possible to utilize these devices in the Landsat image generation program. A laser recorder that generates a direct 9.5" format color Landsat image is reviewed. The advantages of this unit and its use in the Landsat data processing is discussed.

A Laser Color Recorder is described which yields Landsat or similar high-resolution images directly on photographic color film. This development, sponsored by NASA Goddard Space Flight Center, provides the capability for transferring computer-formatted magnetic tape data directly to positive or negative color imagery. Designed to circumvent the current task of reconstructing color images by combining individual (monochrome) color separation negatives, this recorder yields Landsat pictures, directly, with growth potential for the recording of advanced, high-resolution color image sensor data. Three individual laser beams, representing the three primary colors, are modulated separately, then combined precisely to form a single beam of light. This synthesized beam, in which the instantaneous hue and intensity are determined by the modulating signals, is focused on the recording film through a rotating scanning mirror. The entire scanner assembly is translated across the format length to form a raster image directly on the photographic color film.

The Earth Resources Technology Satellite (ERTS, now called LANDSAT) system produces scanned images of the earth, with exposed film presented to the user in pictorial form for interpretation and analysis. Specifications for this output film include MTF requirements, development method requirements, geometric tolerance and the number of DDLs (distinguishable density levels). With regard to the DDLs, the specification requires a minimum of 64 levels of gray at the given resolution, while providing a minimum density range of 2.0. This investigation was conducted both theoretically and experimentally to determine the realizability of this goal with high-resolution photographic film as a storage medium. Assuming, first, that Selwyn's Law is valid for the range of apertures and films in this specific investigation, granularity was calculated as a function of density. A procedure was established by which films can be selected for this task. Several experiments were then performed to evaluate the practicality of these calculations. The results, which were in general agreement, indicated difficulty in achieving the DDL goal with the film selected.

CW room-temperature injection lasers compare favorably with low-power gas lasers in many optical information han-dling applications.

We have selected for this issue of Optical Engineering six papers from the approximately two dozen that were presented at the SPIE seminar on Optical Design Problems in Laser Systems, August 21-22, 1975, San Diego, California.

This is a descriptive survey of the special optical problems which arise in the design and use of lasers. The optical problems, and some of the solutions, related to achieving and preserving spatial and temporal coherence, working with high power beams, and diagnosing laser characteristics are treated.

A number of laboratories throughout the world are actively pursuing the development of pulsed high power Nd:glass lasers for use in their laser fusion and laser plasma interaction studies programs. Perhaps the most ambitious programs in this field have been undertaken by the Lawrence Livermore Laboratory where several irradiation facilities are in opera-tion and where the 4-arm ARGUS and 20-arm SHIVA lasers are currently under construction. These systems are designed to provide the energy, power and wavefront uniformity required to spherically implode nuclear fuel targets such as the deuterium-tritium (DT) solid sphere, in an effort to achieve thermonuclear fusion through inertial confinement.

Laser light can be used to cut and cauterize tissue. At the present time CO2 lasers at 10.6 um, argon ion lasers in the blue green part of the spectrum, and Nd:YAG lasers at 1.06 um have operational characteristics which make their use in surgery potentially valuable. In this paper, the optics presently used to deliver the light from these lasers to surgical targets are described. Since there is little optical design information available for existing devices and since a great deal of improvement is possible, most of the discussion is concerned with proposals for achieving improved performance. In addition, a discussion is included of safety precautions for both patients and operating room personnel.

This article is a survey of the characteristics, technology and applications of lateral interferometry, LI. Some of the early uses of LI in laser Doppler velocimetryl have been greatly expanded to cover new important applications in industrial instrumentations and precision, noncontact measurements. In general, LI uses a high precision optical interference pattern that is projected onto a volume in which the measurement takes place. The measurement technique involves the use of a low power laser beam (milliwatts) which is split into two beams of slightly differing frequency using a Bragg cell. When the beams are brought back together, they form an accurate fringe pattern in space. This fringe pattern is then used as a precision optical scale against which-items to be measured are compared. The fringe pattern can be adjusted to have a spatial period from submicron spacing up to several hundred microns and wider. Receiver optics and the electronics that follow detect the relationship of the fringe pattern to the item being measured. The technique is sensi-tive to the angular orientation of the item, so small angles or variation in angular orientation of an object with high resolution can be measured without making physical contact. In addition, the accurate fringe pattern can be used to measure the optical fidelity (transfer function) of lenses and optical imaging systems. One of the newest developments highlights important applications in the areas of rapid, non-contact monitoring of submicroscopic surface defects on high quality surfaces, such as semiconductor blanks that are used in IC component manufacturing, high quality optical surfaces and the like.

Coherent Optical Adaptive Techniques offer promising solutions to problems of phase distortions occurring in optical systems or produced by the atmosphere. A review of several basic COAT system concepts is presented along with a discussion of the basic hardware components required to implement such systems. Experimental and computer simulation results are presented that graphically demonstrate the ability of COAT systems to compensate propagation distortions in both imaging and transmitted-beam applications.

The design of optical components for high average power lasers requires some additional and unique considerations not present in low power systems. Most common components simply cannot survive in the hostile environment of a high power laser beam. The most successful approaches are those which most constructively deal with the problem of the absorption of laser radiation and the removal of waste heat, while staying within an allowable beam distortion budget. This paper contains a discussion of the problems and promise of four high power components: solid windows, aerodynamic windows, high reflectance mirror coatings, and pulsed damage resistant mirrors. The state-of-the-art performance of these optical elements is discussed. Finally, some crucial issues which must be resolved if applications of high average power lasers are ever to become routine, are enumerated.

This paper presents an error analysis for an airborne radiometric system. The system under scrutiny is a scanning radiometer operating at two wavelengths in either a warm or cold mode. Each wavelength channel consists of an array of N detectors. The long wavelength channel is used for display purposes (acquisition, tracking), whereas both channels are used for data reduction purposes. The data are recorded on analog and digital tapes (both sensor as well as general housekeeping data), reformatted and made ready to undergo stan-dard Fortran type operations. The sensor data consist primarily of target voltage waveforms interspersed among erroneous voltage pulses and white noise. It is desired to ascertain the peak values of the target voltage pulses and relate these peak values to target irradiances via the a priori laboratory calibration. Hence, it is observed that the errors can be classified as belonging to one of the following subsystems: 1) Calibration 2)The sensor itself 3) Data processing and reduction

An optical system has been developed for the compact storage and projection of conventional two-dimensional movies. Each frame of a conventional movie is stored holographically on a small area of a photographic plate or film. Successive frames are holographically recorded adjacent to each other on the film. The movie is replayed by scanning a reconstruction beam across the storage hologram and viewing the real image on a diffusing screen. All images are in registration during playback. Advantages of the technique include: compact movie storage, ease of replication of movies, simple projection system and slow-motion capability.

An interferometer is described for the measurement of thin film steps. The instrument is a double-pass polarization interferometer and has a resolution of one nanometer. It is selfcontained and features simplicity in construction and operation. Measurements illustrating its performance are given.

As stated in the last article, we would continue an analysis of the collective system used as a design example. Since this is a continuation of the last article, space will not permit repeating all the data.