In the year 2000 and beyond, space applications and science missions will require data systems that provide near-real time information availability and cost-effective analysis and distribution of information to the user. Key to the solution of this problem will be high-capacity ground-based and onboard data storage capability, compatible with expected mission requirements. During the 1990's numerical computation will play an increasing role in aerospace applications. High-capacity on-line and archival storage is an essential element of computational aerodynamics and large-scale weather modeling. This paper will discuss aerospace requirements and applications for high storage capacity optical disc systems.

Magnetic storage has followed a linear and predictable development of continual improvement from the early 1960s but is rapidly approaching the point where physici limitations restrict increased capacities. Optical storage, not affected by the si limitations, offers the greatest potential for increased capacities for high-densil storage.

Hole forming media are attractive for achieving high density archival information storage by means of optical recording techniques. Apart from this high date density, a number of other characteristics of the medium like bit error rate, data integrity, archivability and environmental stability are important too. The purpose of this paper is to present characteristics of the Optical Media Laboratory disk.

This paper describes the optical memory system which has been developed by THOMSON-CSF for validating its concepts and to what extent they are compatible with a product to be manufactured in mass volume. We'll particularly insist on the preformat in the medium, which is used in association with the drive, as this preformat is fundamental for the drive to perform its own operations.

This paper gives an overview of the optical media unit design. Information about the optical storage subsystem provides an understanding of the optical media unit design rationale. The paper also includes an assessment of media unit design specifications dictated by the optical storage unit design and market requirements. Such requirements define price, performance, size, weight, and ease of handling. Specifications determined by storage unit, library and human interfaces are also considered. A discussion of the design implementation is also presented.

There has been significant interest and activity in recent months regarding the specifications for and standardization of optical disk recording media. The purpose of this paper is to present a general template to be used as a guideline in specifying optical disk recording media, and a definition of the parameters to be measured, controlled, or specified during the testing and characterization of the optical disk media.

Novel optical disk configurations that use coated webs are described. These include the Kodak Sealed Disk Assembly, which is made from webs held permanently in tension by a peripheral ring structure, and various sized rigid disk substrates to which are laminated coated webs. Such Laminated Disk Assemblies can provide the familiar mechanical properties of aluminum and can be protected from dust in a number of different configurations. Read/ write performance of the disk configurations is given, and media stability data are discussed.

To be successful the emerging technology of optical information storage must provide the end user with both significant performance advantage and cost advantage. The forces that drive the media to low cost are to a certain extent contradictory to those parameters that result in a low cost drive. The 3M media construction is an approach that preserves the low cost potential of a plastic molded disc and yet allows low end drive operation.

The Drexon® medium is no longer a research project. After six years of research, development, and product engineering, it has emerged into a family of optical-data storage products. First delivered as a 30-cm disk in November 1980, this material is now available in card, tape, and minidisk formats. The card and tape products evolved from a fundamental differentiation--mass memories versus compact memories. Our original work concentrated in the mass memory area where 0.8-micron holes and 2 gigabytes per disk are desired. Today, approximately one-half of our effort is in this area. The other half is directed at compact optical data storage, using 5-micron holes and data capacities of 2 to 50 megabytes. The appearance of this market for compact memories parallels the emergence of the personal computer age. Our goal in the mass memory disk area is to develop long-life, low-cost products with sufficient sensitivity, CNR, and bit-error rate performance for advanced digital-data storage systems. Our goal for compact memories with similar qualities is to link our laser recordable cards, software ROM cards, and microtape cassettes to personal computers, video game machines, and office automation products.

The National Bureau of Standards and the National Security Agency jointly sponsored a Workshop on Standardization Issues for Optical Digital Data Disk (0D³)1 Technology, on June 1-2-3, 1983. The workshop was undertaken in response to the growing interest in the standardization possibilities for optical digital data disks as well as in the current OD3 technological and marketing developments. The workshop presentations and panel discussions w ere selected in order to allow the participants to examine the technical and applications issues associated with OD technology; to discuss standards possibilities; and to determine the direction for potential OD³ standardization. Current and future OD³ users, manufacturers, and technical experts presented papers, and participated in both panels and open discussions.

The importance of standards for media interchange is discussed, with particular regard to their application towards the emerging technology of optical data storage.

Background planning considerations for the disk platter design and the cartridge design are presented. Evaluation of these against technical requirements is considered. The resulting designs are presented and some test results are discussed.

The thermal evolution in thin-film multilayer Optical Storage Media (OSM), upon exposure to a writing pulse, depends upon recording system parameters and both optical and thermal properties of the OSM. This paper presents a model of the process that accounts for the distribution of heat generated in the absorbing layers and both axial and transverse thermal diffusion. Once the physical characteristics of a mark generated in the OSM have been predicted, readback performance is modeled under various detection schemes and drive parameters.

A non-antireflective polymer-metal bilayer structure, encapsulated inside a closed cons-truction/is used for digital data storage in the Thomson-CSF Gigadisc. In this paper, a simple model is presented for microdeformation recording in the medium. This model enables a good understanding of the readout signal as a function of the recording power and leads to some practical consequences. Useful polymers and metallic layers are identified and the disc performance is reported. It is shown that recording using laser diodes can be performed at bit rate up to 14 Mbits.s^-1 with a laser power of 7 mW at the disc entry face, in case of a 1200 rpm disc speed. Moreover a working range of 4 m_W, as defined by a 3 dB attenuation, is demonstrated. Discs from pilot production exhibit raw bit error rates at the level of 2.10^-5. For usual environmental conditions, the disc behaviour is compatible with shelf-and archival life at scale of 10 years. Finally, the processes for both layers deposition and disc construction are easy and cost effective. It is concluded that Giaadisc can successfully enter today the market place.

The optical recording characteristics of Drexon® optical memory disks have been evaluated at two krypton ion laser wavelengths, 647 nm and 799 nm. Reflectivity modulation and carrier-to-noise ratios were obtained at each wavelength for several input parameters. These parameters included optical reflectivity of the media, incident laser power, media velocity, and recording pulse frequency. Optical and electron microscopy were used to evaluate the appearance of the recorded pits. Measurement results are presented.

The optical data disk consists of a rigid substrate, a thin film multilayer coating, and a transparent overcoat. The optical behavior of the data disk is determined by the thin film trilayer which includes a reflector layer, a non-absorbing dielectric spacer layer, and an absorbing recording layer. The reflector layer is an opaque metal film with high reflectance, typically aluminum, silver, or gold. The spacer layer serves to place the recording layer near a peak in the standing wave that is formed by the interference of forward and reverse flowing waves in front of the reflector. The recording layer is a semitransparent layer of an absorbing material with selected optical and thermal properties. Regions of the recording layer that are heated by absorption and retention of incident energy suffer an irreversible change in physical and optical properties that leads to a written data bit. Discontinuous gold films, frequently referred to as island gold films, offer several advantages in this application. When heated by the absorption of radiation in the trilayer configuration, the islands coalesce, the optical absorption of the island film diminishes, and the trilayer reflectance is changed significantly. The optical behavior of this trilayer is predicted with a particle-size-dependent Maxwell-Garnett model for the island film. This paper begins with a description of the trilayer from the viewpoint of the thin film designer. Then the Maxwell-Garnett model for the optical properties of an island film is introduced. The two theoretical descriptions are then combined to predict the behavior at the helium-neon laser wavelength (633 nm) of a trilayer which contains an island gold recording layer. LaBudde, LaBudde, and Shevlinl presented a comprehensive description of the optical data disk structure which is the subject of this analysis. The optical data disk consists of a rigid substrate, a thin film multilayer coating, and a transparent overcoat. Figure 1 shows the trilayer cross-section and identifies the elements and the optical parameters of interest. Interference within a thick transparent over-coat is not important because the data disk is used with a focused cone of laser light.2 Therefore, the overcoat will be treated as a medium of infinite extent.

The development of an optical disk tester can be as demanding as the development of a production optical disk drive, especially if the tester does not have a companion drive program from which to draw hardware resources. For this reason it is prudent to set realistic targets for tester capability at the onset of a development program as the difficulty of the task is a strong function of the number of test capabilities assigned to the tester. This paper presents considerations and guidelines to assist in the planning of a disk tester. Specific issues addressed are: realistic measurement capabilities, the control of disturbances, measurement techniques. and calibration considerations and techniques. In addition to a general overview specific examples of measurement and calibration methods are presented. Also discussed in this paper are the special considerations associated with high throughput production disk testers.

Kodak has Hevised and demonstrated an optical data recording medium using stretched polymeric sheet as a substrate for a coated dye-polymer laser recording. layer. The recording layer is protected by a second stretched, polymeric sheet, parallel to, and 250 pm away. from, the recording sheet- The two sheets are held in tension by an annular metal rim. A plastic centering hub is bonded, to the center of the sheets to allow removal and recentering of the recording medium, (called a sealed disk. assembly - SDA). The SDA is designed to be pulled down over two concentric, annular reference surfaces on the drive platen. The recording sheet stretches to take on the plane defined by the two reference surfaces. Performance data will be presented, on vertical planarity of the recording surfaces, recentering capability, track shape fidelity, and results of temperature and humidity conditioning.

A digital record and playback capability has been added to an existing laboratory recorder. Techniques for the measurement, of bit. error rates and burst-error statistics are presented and applied. to data stored in a solvent-coated optical recording medium.

The long term storage of DOR disks was studied for application as a long-term data storage medium with respect to degradation under high humidity conditions. For this purpose a standard test with high humidity (95%), and cyclic temperature (25 - 65°C) was used. Besides these accelerated aging tests on hermetically sealed sandwiches, we also investigated non-sealed disks in order to optimize the lacquer, the Te alloy composition and its thickness. During interruptions and after aging the relevant optical recorder parameters were measured. These were optical transmissivity, reflectivity, in-track clock-to-noise ratio, sig-nal-to-noise ratio of written data, threshold energy for ablative recording and the bit error rate. The various types of aging phenomena observed in the "open" sandwiches are discussed. Cyclic climate tests on open sandwiches with Te based alloy films containing 60 - 85% Te show that some alloy lacquer combinations have substantially decreased performance after 30 days of testing, whereas disks with pure Te films cannot withstand such severe conditions for more than a few days. Experiments on sealed disks show that the aging of sensitive films only starts after failure of the seal. On the basis of these experiments, the usability of OML disks is expected to exceed comfortably the requirements for application in long-term data storage under office conditions for periods of longer than ten years.

The use of tellurium based optical disks under office conditions is discussed. Data on the physical and chemical properties, toxicity and existing legal regulations are presented. The conclusions are that in the use of the disk no special precautions are necessary and that a label should give advise about disposal to avoid any risk to the users.

In optical recording it is essential that the laser beam stays in focus on the sensitive layer of the optical disk. The focussing performance depends on the variations in the optical path during recording and on the ability of the objective lense assembly to correct for these deviations. The vertical displacement of optical media rotating at 8 Hz is corrected by servo-mechanics and servo electronics of the focusing objective lense assembly. Typical values for the vertical displacement due to media unflatness for the Philips - C.D.C. optical recording system, are:

An improved configuration for the Philips Air Sandwich Disk' is described that is compatible with high speed, high density recording. Major advantages include: improved balancing capability, more accurate and repeatable self-centering on the turntable spindle, flatter substrate profile during rotation, and relatively simple assembly without the requirement for accurate substrate tolerances. The centrifugally induced pressure gradient within the rotating air cavity and how the improved design deals with this phe-nomenon is addressed.

Several materials including Te, Te:Bi, and Sb₂Se₃ have been studied for use as a write/read/erase absorbing layer in a capped bilayer or trilayer structure, using Al₂0₃ as the phase and capping layers. Discs have been obtained that yield a fully erasable 49dB SNR measured in a 4.2MHz bandwidth and can be recycled at least 500 times. For the materials reported the data retention time is on the order of 4 to 6 hours.

Vanadium dioxide undergoes a thermally induced first order phase change from semiconductor to metal near 67°C. In thin-film form, significant optical contrast can be produced at visible wavelengths on switching from low to high temperature phases. If the film is locally heated (e.g. by means of a laser) so that the temperature is driven above the transition point, the color or reflectance is changed only in that local region. Upon removal of the heat source the temperature returns to equilibrium. The local contrast, however, is either removed (dynamic operation), or stored indefinitely (memory operation) depending on the equilibrium or "bias" temperature. This storage option is possible because the material deposited as a thin film exhibits hysteresis, i.e., the curve describing the state of the film vs. temperature is double valued in the transition region. In order to erase information from a film region, that region must be lowered in temperature to a level below the onset of hysteresis. The general properties of vanadium dioxide thin film suggest a material suitable for recording optical information in a high density, digital format allowing erasure and reuse. Practical feasibility has been examined at Vought during the past year by a series of performance measurements. For example, laser writing of one micron diameter spots in less than 50 nanoseconds has been accomplished, and the amount of energy required for writing is compatible with laser diodes. These measurement results and data on contrast, storage time, and film surface morphology will be presented. The size of individual crystallites comprising the vanadium dioxide film is expected to fix ultimate spatial resolution.

A suboxide thin film of TeO_x ( x is smaller than the stoich.Lometric value ) containing a small amount of additives of such metals and semimetals as Sn and Ge has been found to have the property of showing a reversible change in its optical constants when the film was exposed in turn to two diode laser spots with different sizes, and this property can be utilized for an erasable disc. For recording, a TeO_x thin film deposited on a PMMA substrate is irradiated by a diffraction limited laser spot, 0.8 pm in dia., modulated in response to an input electrical signal. This causes a micro-sized area of the film to be suddenly heated and rapidly quenched, resulting in a decrease in optical reflectivity. This recorded bit can be erased at real time by the irradiation of a diffused laser spot to an elliptical shape, 1 x 10 pm, by which the bit recovers its optical properties. An optical head having the two laser beams, one for recording/playback and one for erasing, has been developed. Real time erasing and recording at the same time has been achieved for a video signal. In excess of a million record/erase cycles have been demonstrated with no significant degradation in playback signal quality or erasability. Carrier-to-noise ratio, C/N, was more than 55 dB at 5 MHz, 30 kHz bandwidth.

Optical mass data storage systems have developed to the point of application. The advantages of the optical techniques are packing density and increased data rates with random access for retrieval. The key to improvement is the record material; although acceptable archival materials have been developed, progress continues with more efficient techniques and materials to increase packing density, S/N, and data rates. However, to qualify for total competition with magnetic storage systems, it is necessary to provide an erasable and reusable medium, which this paper will discuss.

Two erasable optical recording materials were evaluated for use in direct digital spot recording systems: a photodichroic from Corning and a photochromic from Plessey. The materials were tested in a static system to isolate the material parameters from the system characteristics. Both materials have potential for data storage applications. The photodichroic has the sensitivity, frequency response and noise characteristics for direct spot recording and has an amplitude readout mode. The photochromic has the necessary recording properties but requires a phase readout system. For both materials, the coating parameters must be optimized to meet the specific system requirements.

An erasable optical disc memory with smectic liquid crystal (LC) as the active medium has been fabricated and tested. Using appropriate dark field optics, we have demonstrated writing, reading and erasing at data rates of 13.5 MHz with a bit spacing of 1.25 microns. Although not all problems with this memory have been solved, we think the concept is viable with an expanded research effort in materials and system aspects.

High-bit-density optical data storage disks based on reversible crystalline-to-amorphous phase transitions are discussed. Some of the factors controlling the performance of such disks are the signal-to-noise ratio, error rate, and stability, each of which imposes stringent requirements on the active material, geometry, and write/erase/read mechanisms. We have developed a reversible optical data storage disk based on materials in which tellurium or other chalcogens play an important role. Such alloys are called chalcogenide materials, and are highly flexible and capable of independent optimization of the relevant materials parameters. In particular, composition, preparation techniques, chemical modification procedures, and coating methods can be tailored to achieve system optimization. Furthermore, disk geometry, fabrication, and crystallization and vitrification processes can be designed to improve the overall system performance

We on high density recording experiments of erasable digital information in magneto-optical amorphous layers on pregrooved discs. The recording and reading of informa-tion is done on a recorder provided with an AlGaAs laser and equipped for polarization-sen-sitive read-out of the Kerr effect. The signal-to-noise ratio and the bit error rate of the recorded information have proved to be sufficient for an information density up to 0.4 Mbit/mm².

The scope of this work is to create an alterable and erasable quantum-mechanical laser disc mass memory. The new memory system is based upon optical quantum-mechanical bistability of electron spin systems, created with laser in the ferrimagnetic thin-film (YIG) of a fast rotating Garnet disc (GGG). The microscopic elements of the new memory system are certain photomagnetic cylinder domains and their surrounding, oppositely magnetized toroidal shells. They are characterized either as "black" or "white" electron spin-flips. Electron spin-flips are created near laser focus by means of the angular momentum of an incident, circularly polarized laser beam. In order to create electron spin-flips, the intrinsic ferrimagnetic domains of the Garnet are to be circularly prealigned with laser by thermomagnetic means. The incident laser beam is signal modulated in square waves by means of a linear electro-optical modulator (Pockel's cell), yielding electron spin-reversal (spin-flip) along the concentric thermomagnetically prealigned circular domains of the ferrimagnet. A combined elementary cylinder and its shell comprise a digital photomagnetic electron spin state of plus one (+1), or minus one (-'4), where (h) is Plancks constant divided by 2π. The empty intrinsic state of the cir-cularly prealigned elementary domains comprises the third neutral state zero. Quite different from the optical bistability of volatile semiconductor memories, photo-magnetic bistability is nonvolatile due to the coercive force of the ferrimagnetic thin film. Magnetization stays permanent until it is erased by thermomagnetic means. The theo-retical bandwidth of the new memory is of the order of one (1) Gigahertz, corresponding to the free angular precession frequency of the electron spin-flip, which is determined by the Larmor frequency of the intrinsic magnetization of the ferrimagnetic domains of the Garnet.

In the first part of the paper, we compare the predictions of our earlier theoretical work on the signal-to-noise ratio for magneto-optic read-out with experimental measurements. We then examine how the thermal response of the medium can be tailored to the light level available for recording to further enhance the SNR. In the second part, we examine theoretically the writing and erasure processes. We calculate the various contributions to the energy of formation of a domain during a typical writing cycle under an applied field and obtain some design constraints on both the medium and system that are required to ensure single domain formation in writing and good reversibility in erasure.

Based on the optical and magneto-optical properties of single crystalline CoFe₂0₄, the enhancement of magneto-optical rotation in thin CoFe₂0₄ films has been studied. It will be shown both theoretically and experimentally that the rotation can be increased considerably by optimizing the thickness of the CoFe₂0₄ film in combination with auxillary non-magnetic thin films. F8r readout at AlGaAs laser wavelengths ( ~800 nm) this resulted in an overall rotation of 8^o at 20% sample reflectance.

The stability of reverse domains in thin films of magnetic materials having high coerciv-ity is investigated. It is shown that domains below a critical diameter are unstable and will collapse. To minimize this minimum domain diameter it is necessary to minimize domain wall energy while maximizing the product of magnetization times coercivity, M.H_c. Since M.H_c tends to be nearly a constant near the magnetic compensation temperature, it is concluded that domain wall energy a and the product M-Hcare critical parameters for assessing the use-fulness of a material for high density thermomagnetic recording applications.

Magneto-optic media are an attractive method of achieving high density erasable information storage. Several parameters are important in the dynamic characterization of these media, including C/N ratios, sensitivity, erasability, magneto-optic rotations, and reflectivity. The purpose of this paper is to report these and other media characteristics for a newly developed, high signal to noise ratio magneto-optic media.

Recent efforts to improve the media sensitivity of optical recording have resulted in the development of various multi-layer constructions and in particular, the optically tuned anti-reflective trilayer configuration. In order to further enhance the recording sensitivity, many trilayer media use low melting materials such as tellurium or tellurium alloys for the light absorptive layer and/or a light transmissive layer that is easily sublimable, decomposable or vaporizable by the laser heat. In general, these materials compromise the media stability such that some form of environmental protection is required to ensure archival storage.

The pulse width transfer function of a Te-alloy optical disk is measured for a wide range of write laser powers and disk velocities. It is shown that a simple model can provide a quantitative explanation of the data.

A detailed study of the effects of the subbing layer surface energy on the laser writing sensitivity, optical properties (reflection, transmission and absorption) and lifetime of Te and TeGe films is reported. A continuous spread of surface energies is obtained by using plasma deposited teflon and spin coatable methyltrifluoro-methylacrylate-co-methylmethacrylate polymers of a range of compositions. Based on these studies it is concluded that low surface energy surfaces do not improve the mature hole opening threshold of TeGe films and that the improvements seen for Te films are likely due to changes in the film microstructure. The observed comparatively poor lifetime performance of Te films deposited onto low surface energy surfaces can also be explained by microstructural changes.

Laser writing sensitivity, contrast ratio, and archival stability are used to evaluate Te and various Te-alloy thin film media for optical data storage application. The alloys studied include Te-Se, Te-Ge, and Te-Bi. Optical properties pertinent to laser writing sensitivity and contrast ratio such as light absorption and reflectivity are reported for these films. No significant degradation in the light absorption and reflectivity are observed if the concentration of these alloying elements is less than e.g., 1 Owt% . The stability of these films is studied by monitoring the change in light transmission, measured both over a large area and locally using a scanning laser beam. The presence of this small amount of alloying elements is found to significantly improve the chemical stability of Te films. Examples concerning the physical stability of amorphous optical recording media are presented and discussed.

Optical disk media para.oeters are examined with respect to recording capability, dimensional constraints, and the necessary interface with recording equipment. The parameters discussed include recording properties such as Media sensitivity and recorded signal quality. The mechanical dimensional tolerances required to proimote media. interchange ability, and to permit effective optical tracking and focus control are also discussed. The stated values reflect the current understanding of requirewents for automated, optical disk systems, and the reasons for the selection of these values are presented. A recording equipment of primary interest is the multidisk jukebox, with its requirements for disk protection and automated. deployment. Consequently, emphasis is given to the interface of disk media with the optical and mechanical subsystems of random-access, multiple-disk equipment.

The possibility of using a reverse trilayer media concept as one of the means of continuous lower cost of the optical storage appears advantageous. The basic concepts, potential advantages, challenges as well as the preliminary results are presented.

The interaction of light with matter can be well described in simple systems. Understanding the nature of this phenomenon with respect to optical disk recording, however, is complicated by the time dependence of the properties of the interacting medium and the short time scale of the interaction. Yet to improve media performance and sensitivity, the details of the recording event must be understood. Because the event is not directly observable, the interaction must be studied indirectly using the tools at hand. Elucidating recording mechanisms entails reconciling these observations with the physical processes considered from both thermodynamic and kinetic viewpoints. Over the years, researchers have used this approach to probe the mechanism of recording in a number of write-once recording media. The progress in this area will be reviewed.

The long archival storage lifetimes projected for optical disk media have generated a need for good assurances as to media stability and data integrity. Several comments are made concerning parameters and mechanisms for media degradation, points to keep in mind in accelerated environmental testing, and several simple semi-empirical models are proposed as a means of simulating and summarizing test data.

Various sources of noise on Te-alloy optical recording disks are isolated and examined. Examples of disks in which substrate, Te-alloy coating, or recording noise dominates are presented. When a Te-alloy medium is properly chosen to minimize its coating and writing noise, a disk using a typical polymethylmethacrylate substrate has a carrier-to-noise ratio in excess of 60dB with a 30KHz bandwidth. For these low noise Te-alloy based disks, the substrate noise dominates.

A high-performance optial recording disc has been developed. The recording material is so sensitive that the disc can be recorded and played back by a single optical head using a commercially available laser diode. The recording sensitivity of the disc is enhanced by the unique double-layer structure consisting of a recording layre (Sb-Se compound metal) and a heat absorbing layre (Bi-Te compound metal). In the signal recording process, the recording material changes its physical phase from amorphous to crystalline, when it is heated by laser at 170°C . This phase transition triples the reflectivity of the recording layer. Because the phase transition occurs over a narrow temperature range of about 20 degrees, the pit edge of the recording layer becomes sharp and its pit length is rigidly determined. This ensures a high carrier-to-noise ratio over a wide frequency range. The newly developed disc is, therefore, not only capable of digital recording but also adapt to any pit-length change necessitated by analog video recording. Since the disc recording is facilitated by the changing of the optical characteristics of the recording material, the physical disc form is never affected by laser heat, i.e., neither melted nor evaporated. Therefore, the signal surface can be directly sealed by a protective layer and the disc offers higher storage reliability and greater ease of operation. Direct sealing of the signal surface by protective film also makes a double-sided disc structure possible, enabling the disc to record on both sides. This structure increases the flatness of the disc and enhances its recordability and playability significantly. The new disc will be applied to mass storage as high-performance and massive-information recording medium.

A new simple method was developed to make a groove on an optical memory disc. This uses the swelling of the Te-C material. A bulged line is formed by irradiating laser light onto the Te-C layer which has a thin metal layer over it. This dry process is called the Ω(OMEGA)-process from the sectional shape of the groove. The Ω-disc should have a lower error rate and a higher track density than the disc made through a conventional wet process.

Results are presented of substrate incident optical recording experiments at A1GaAs laser wavelengths on pure, amorphous, solvent coated, dye layers. Upon laser irradiation pits with a rim are formed, which increase in width and depth with increasing pulse energy. The information is read out at the recording wavelength as reflection changes relative to the dye layer reflection.

An organic dye medium has been developed for diode-laser high-density recording. The new medium, having a single layer structure, can be recorded and played back by a laser diode through a substrate. It provides 54 dB signal to noise ratio in a 30KHz bandwidth at 2.5MHz carrier frequency. The medium shows excellent properties for long-term stability.

Thin films consisting of an organic dye dissolved in a polymer binder have been shown to constitute a viable medium for high density optical recording and storage of information. An investigation has been made which addresses the influence of the polymer binder on the marking process in this type of medium. Time resolved measurements on a series of films, in which the molecular weight of the polystyrene binder is systematically varied between 2.1 K and 2000 K, have revealed a molecular weight dependent relaxation phenomenon which occurs subsequent to the initial hole opening. The relaxation phenomenon appears to be a flow of displaced molten polymeric material back into the initially created hole. This relaxation process becomes important at a molecular weight of 37 K a value close to the critical molecular weight where chain entanglements occur and where the melt viscosity becomes strongly molecular weight dependent.

Discontinuous metal films have been recently proposed as a potential archival optical storage material. This class of materials exhibits a unique writing mechanism that yields relatively low writing energies even when materials with high melting points are used. Here, the physics of this writing mechanism are examined. Transmission electron micrographs of exposed areas clearly indicate that the writing mechanism is laser induced coalescence of the metal particles resulting in a dramatic change in optical properties. It is shown that the observed coalescence mechanism is consistent with a theoretical analysis for the sintering of small particles. Calculations based on this mechanism indicate that writing can occur at temperatures well below the melting point of the bulk material. However, detailed thermal modeling of the writing process coupled with measured threshold energies, indicates that melting almost certainly occurs. Furthermore, experimental results indicate a sharp threshold to the writing process. This is inconsistent with the theory of particle coalescence, but a necessary characteristic for a practical optical storage material. This threshold can be attributed to the necessity of bringing the metal particles into physical contact before coalescence can proceed.