A recent survey of the needs of the optical industry concluded that improved specifications and methods of measurement of optical component flaws are an outstanding requirement. After definition of the terms involved, the effect of flaws on the cosmetic quality and function of a variety of different optical systems, together with the benefits likely to be derived from their measurement, are described. Techniques for inspection using probes and area methods employing light scatter are reviewed against the background of existing standards. The case for a new approach to quantify flaws in terms of photometric obscuration, rather than surface area, is presented with a description of a typical instrument able to quantify the amount of light removed from a beam by a flaw compared with a standard flaw which removes all the light. Finally, the present level of international activity concerning standards relating to flaws is discussed with recommendations regarding the future.
The design characteristics of a laser such as the wavelength of operation and the power level influence the type and properties of the substrate material which will be useful for the particular application. Optical material for near UV, visible, and near IR applications will be discussed, with the main emphasis on glass. The properties of the optical material which are of primary concern are the transmission range, striae, birefringence, homogeneity, and inclusions. In certain applications the laser damage threshold may be of importance. Each of these properties will be discussed.
The problem of selecting an infrared optical material for a laser is complicated by the many types of laser devices and the large number of potential optical materials available. The authors have described a methodology to design an optical window for an infrared laser, and illustrate this method by specific examples and analyses. This paper considers transmissive infrared materials over the wavelength range of 2-14 pm which encompasses the most widely used infrared lasers - HF, DF, CO, CO2 and N20. The physical data for sixteen (16) potential infrared transmissive materials are provided for reference. The methodology considers the important mechanical, thermal and optical issues. Although each laser application problem is unique, the techniques described can be applied to a wide range of devices and laser characteristics.
This paper will review the specifications of diamond machined optical components with special emphasis on manufacturing considerations. The specifications are divided into several topic considerations. These are: material considerations, optical surface descriptions and evaluation techniques, single-point machined surface texture, defect and cosmetic considerations, coating, plating, surface finishing and environmental considerations.
The coating of large laser optics has all of the usual features of the coating processing of any high power optic but with the complication of large mass, extremely high cost, and sometimes a sensitivity to changes in figure. Increased risk and the critical issues, therefore, mainly result from the great bulk and attendant difficulties in handling, cleaning, heating, cooling, and other process steps with the optic. In addition the materials, size, and configuration used in the construction of the optics can cause difficulties and even compromise in the ability to deposit quality coatings. Potential problems are possible outgassing, the use of soft chemically active surfaces that might compromise the cleanability, poor uniformity of coating thickness that may result from the large thermal mass or complexity of modern laser parts, and the handling difficulties that might arise due to the large weight and cost. The result is a need to take extra special care in the coating process to insure adequate safety and performance. There are also optical effects due to the geometric shapes in modern optical systems and environmental durability effects on the coating from the environments in which the optics are used that must be con-sidered in order to insure adequate system performance of the laser device. The particular issues, the required areas of specifications and the possible coating process limitations are discussed for each of the critical phases of the large optic coating process.
Laser imaging and transport systems are considered in the regime where laser-induced damage and/or thermal distortion have significant design implications. System design and component specifications are discussed and quantified in terms of the net system transport efficiency and phase budget. Optical substrate materials, figure, surface roughness, coatings, and sizing are considered in the context of visible and near-IR optical systems that have been developed at Lawrence Livermore National Laboratory for laser isotope separation applications. In specific examples of general applicability, details of the bulk and/or surface absorption, peak and/or average power damage threshold, coating characteristics and function, substrate properties, or environmental factors will be shown to drive the component size, placement, and shape in high-power systems. To avoid overstressing commercial fabrication capabilities or component design specifications, procedures will be discussed for compensating for aberration buildup, using a few carefully placed adjustable mirrors. By coupling an aggressive measurements program on substrates and coatings to the design effort, an effective technique has been established to project high-power system performance realistically and, in the process, drive technology developments to improve performance or lower cost in large-scale laser optical systems.
The combined requirements of energy density, multiple wavelength, and aperture make the coatings for the Nova Inertial Confinement Fusion (irF) laser unique. This ten beam neodymium glass laser system, built at the Lawrence Livermore National Laboratory (LLNL), has over a thousand major optical components; some larger than one meter in diameter and weighing 380 Kg. The laser operates at 1 054 nm and can be frequency doubled to 527 nm or tripled to 351 nm by means of full aperture potassium dihydrogen phosphate (lePP) crystal arrays. The 1.0 nsec fluence varies along the laser chain, sometimes reaching values as high as 16 J/cm2 at the input lens to one of the spatial filters. The design specifications of this massive optical system were changed several times as the state-of-the-art advanced. Each change required redesign of the optical coatings even as vendors were preparing for production runs. Frequency conversion to include shorter wavelengths mandated the first major coating redesign and was followed almost immediately by a second redesign to reduce solarization effects in borosilicate crown glass. The conventional thermal evaporation process although successful for the deposition of mirror coatings, was not able to produce antireflection coatings able to survive the locally high chain fluences. As a consequence it became necessary to develop another technique. Solution produced coatings were developed having transmissions exceeding 99% per part and damage threshold values equal to the bare substrate. The unique requirement of the Nova laser necessitated special deposition and metrology equipment. These programmatic developments will be reviewed in the context of the cooperative working relationship developed between LLNL and its vendors. It was this excellent relationship which has enabled LLNL to obtain these highly specialized coatings for the Nova laser.
Shiva experiments had shown that the laser beam produced a dense
interacted with the target pellet. This plasma reduced the direct
to the target. In addition, the deuterium - tritium
causing it to expand just prior to the compression
phenomena, plasma and preheating, reduced
plasma when it
coupling of the laser
fuel mixture was being preheated,
stage of the process. Both of these
the efficiency of the thermonuclear burn.
The optical coating requirements for high energy laser systems have advanced the state-of-the-art in coating design and manufacturing technology over the past decade. This paper is intended to provide guidance with respect to the spectral properties that can be achieved in practice with current manufacturing technology. The key to specifying functional and cost effective coatings is separating what is possible from what is practical. Realistic specifications are presented for several generic types of coatings relevant to high energy laser optical systems in the spectral region from 230nm to 2000nm.
This paper approaches the topic of Laser Beam Image Recording from the user's perspective. It discusses the parameters of concern to a system group charged with specifying a high performance Laser Beam Image Recording Subsystem. The paper concentrates on those parameters that have significant impact on interface complexity, image quality and cost. A block diagram of a typical Laser Beam Recorder is shown along with a brief explanation of the following subsystems: Image Data Interface, Control Data Interface, Image Data Processor, Annotation, Scan Data Processor, Command and Control, Electro Optics, Film Transport, and Built-In-Test Equipment. Ranges of the following signal parameters are given: Line Rate, Data Rate, Data Duty Factor and Bytes/Line. Typical values of the following critical image quality parameters are given: Resolution, Raster and Banding, Geometric Fidelity, and Density Fidelity. Each of the critical parameters are defined and measuring techniques and equipment discussed. A list of system level questions which a user should consider when formulating the Laser Beam Recorder specification are also presented.
Like most other engineering efforts, specifying scanners is a balancing act between objectives and constraints. There are numerous papers given each year about specific sys-tems, how their particular objectives were achieved, and some of the resulting specifications. In contrast, this paper treats the objectives and constraints of laser scanning in a generic way, so as to reveal the commonalities of such systems. The resulting outline (figures 4 thru 7) should be used as a checklist to test the completeness of any particular scanner specification. A distinction is made between specifications whose purpose is "design control" and those whose purpose is "performance verification". Finally attention is focused on specifying "jitter", one of the unavoidable error factors in scanning systems.
Laser specification criteria for both image and optical disk recording/playback are discussed. In laser image recording, the choice of laser wavelength is dictated by the spectral sensitivity of the recording film. Laser power required is determined by the film sensitivity, maximum density, and maximum film area exposed per second. Argon and helium neon lasers have been employed in image recording. High power argon ion lasers have been employed for extremely high data rate and packing density optical disk recorders. These recorders have employed multiple beam techniques and "jukebox" configurations to provide data rates greater than 500 Mbps, and data storage of 1 X 101 bits per side of a 14-inch disk. Laser diodes have been employed in rugged and/or compact data storage devices to provide data rates up to 25 Mbps per track, with multiple diodes for multiple tracks, and data storage up to 5 x 16° bits per side. Laser specifications such as beam power, noise mode and angular sta-bility, physical size, and cooling requirements are discussed.
Specifying a rotating polygonal mirror and drive system involves a careful analysis of the complete optical scanning system it is used in and the specific effects of each characteristic of the beam deflector on system performance. This would appear on the surface to be straightforward, however there are subtleties that may evade the most conscientious and diligent specifier. The intent here is to identify same pitfalls the specifier should be alert to.
The process of specifying a pre-objective scan lens involves consideration of first-order constraints different from that of an imaging lens. A simplified formula has been developed to combine the inter-related properties of wavelength, scan length, scan angle, entering beam diameter, and spot size based on both theory and empirical results. Other aspects such as entrance pupil distance, linearity, telecentricity and resolution are investigated to allow for reasonable tolerancing as well as to gauge design complexities and production costs.
With the development of laser diodes and fiber optics, the field of micro-optics has greatly expanded both in the type and volume of micro-optics produced. From a historical standpoint, micro-optics were first developed for microscopes and the design and fabrication of microscopic objectives is a well developed process. A good reference on the fabrication of microscope objectives is W. Zschommler's book "Precision Optical Glass Working". 1 More recently, endoscopes have developed and evolved from periscopic type designs to those utilizing selfoc rod lenses.
In order to discuss the characteristics of laser diodes important to the user, one should discuss the fundamentals of laser diode operation and in doing so point out the characteristics which can vary with device type and construction details or which are not stable with operating condition.
Single mode optical communication systems place stringent demands on the opto-mechanical design. Tight tolerances on the stability of connector and source coupling efficiencies translate to unreasonable tolerances on the optical components and mounts. Current design concepts for fiberoptic interconnection devices are reviewed and their impact on system specifications is discussed.