Nonconventional-shaped optics are being machined for use in laser optical systems. The fabrication processes incorporate special-quality diamond tools and specially constructed turning machines. The shapes produced include axicons (conical-shaped mirrors), waxicons (a compound axicon with a "W" cross section), torics, and multifacet mirrors. Whereas conventional-shaped optics are readily producible by the lapping process, these nonconventional-shaped optics are very impractical to lap. The axicons and waxicons produced were estimated to have surface straightness as good as 5 μin (125 nm), over 3 inches (76 mm) of length, and angular accuracy as good as 2 arc seconds. A toric mirror was estimated to deviate (peak to valley) from a best-fit radius by 4 μin (100 nm) over 2.25 inches (57 mm) of surface length.
Precision machined optics have been used in an experimental study of resonator design concepts for annular gain region lasers. The most practical annular laser resonator tested was a half symmetric unstable resonator that used a precision machined axicon and cone. Included in this paper are photographs of the far-field intensity distribution.
This paper describes the theory, design and fabrication of a complementary pair of cone-like mirrors which transform an annular collimated laser beam into a gaussian profiled collimated beam without obscuration. The details of a simple computer algorithm are revealed which explain the numerical procedure for computing the coordinates of the mirror surfaces. Also discussed is the procedure for diamond turning the nonlinear surfaces using the development lathe at the ERDA Y12 Plant and the metrology of the first parts produced.
Current techniques for manufacturing off-axis paraboloids are both expensive and insufficiently accurate. An alternative method, turning the workpiece about its axis on a diamond-turning machine, is presented, and the equations describing the necessary tool movement are derived. A discussion of a particular case suggests that the proposed technique is feasible.
Optical surfaces produced by machining processes place a great burden on the accuracy of the machine tool system. For example, if the motion is produced by linear slide system and actuated by lead screws driven with gears, the machine is limited in figure and surface finish accuracy. A new machine is described, based on only rotary motion, pivoting on air bearing spindles. The new machine, called an Alpha-Theta machine, affords greater accuracy, elimination of lead screw drives, and also minimizes rewelding of chip material to the cut surface. The Alpha-Theta machine is a new generation single point turning machine.
The current state of machining theory is examined for relevance to micromachining. Of particular interest are those features of the theory which are important to optical surface finishes and surface characteristics. The relation of transverse strain or side flow to the nature of the machining marks is one example of interest. Correlation with measurements of machining parameters and surface finishes is given.
The High-Energy Gas Laser Fusion Program requires several large optical elements containing aspheric surfaces. A fabrication process utilizing diamond turning for figuring has been chosen as the most feasible when considering cost and allowable. time for fabrication. To diamond turn optics of this size (80-inch diameter), a two-axis horizontal spindle, numerical control turning machine was chosen. Improvements in vibration control, tool path control, and size capability were needed to achieve the desired capability. This paper describes some basic criteria needed for diamond turning. In addition, the major modifications required to achieve these criteria in a machine tool are discussed.
Opticians and machinists employ opposing techniques to achieve precision in their work. The optician relies on a subtle biasing of repeated loosely controlled tool motions and statistical averaging to produce polished surfaces with relatively simple geometrical configurations and extremely small surface errors. The machinist, on the other hand, relies on precisely controlled tool motions to produce complex shapes in a single pass. If we are to succeed in single-point turning optics we must design and build machine tools capable of controlling spindle and tool motions to optical tolerances. We will discuss machine tools for single-point turning of aspheric optical surfaces in terms of overall design philosophy, choice of materials, alternate approaches to the implementation, monitoring and control of tool and spindle motions. We will demonstrate, with numerical examples, the magnitude of the problems associated with the construction of these machines.
Precision machined metal mirrors are produced in this Laboratory for use in industrial laser applications. The machining geometry adopted uses a single diamond tool in a high speed flycutting disc on an air-bearing spindle. The tool removes material from a slowly rotating workpiece mounted on a pressurised oil bearing. Plane, cylindrical and spherical surfaces have been machined on aluminium alloy, copper, brass and beryllium copper blanks. These are used as laser cavity, polygonal and beam handling mirrors for use with high power CO2 lasers. A machine which produces mirrors up to 200 mm daimeter is in regular use and 660 mm capacity machine is undergoing trials. Typical plane mirrors are flat to within half a fringe in 30 nun (6328 Å) with a surface roughness of ~100 Å (CLA). The spatial frequency power spectrum obtained from laser scattering measurements is used to identify the sources of vibration in the machining system. This paper discusses machine design parameters, operating and alignment techniques and reports the performance of the mirrors.
Mr. Jim B. Bryan of the Lawrence Livermore Laboratory gave a post-deadline paper describing his work, diamond turning an x-ray microscope. After demonstrating the repeatability to better than 1 microinch (250 Å) corrections were made to the controls of the machine in order to correct for the repeatable errors. The resulting accuracies were very impressive. The following questions were asked of Mr. Bryan after his talk:
Intercomparison of the optical properties of diamond turned, evaporated and sputtered metal mirrors is made with specific reference to surface and bulk physical structure. In most applications, absorption and scattered light are important optical parameters. Both of these characteristics are directly related to surface microtopography which is a direct product of the finishing methods employed. For laser applications, the threshold for damage is also often critical. The properties influencing laser damage include surface microtopography, as well as bulk physical and chemical structure. Diamond turning, in addition to its very attractive manufacturing advantages, can produce optically superior components. Nearly intrinsic values of pulsed laser damage threshold and absorption have been measured on diamond turned copper mirrors.
A Scanning Auger Microprobe was used to examine the surfaces of diamond turned electroplated mirrors and conventionally prepared mirrors. The change in contamination was noted in each, following an ion polishing process and a vacuum annealing process. Carbon and oxygen are the most predominant surface contaminants and are present in the top 12-25A. The depth of contamination was determined by Argon sputter etching the surfaces. Much of the contamination is due just to air. Also discussed are Auger analysis performed in conjunction with our multilayer dielectric enhancement study of 10.6 micron optics. KEY WORDS: Auger spectroscopy, diamond turned mirrors, surface physics, contaminants, dielectric coatings.
The light intensity diffracted out of a reflected laser beam as a function of angle can be used to determine a portion of the spectral density function (SDF) of the reflector's surface. These measurements cover the frequency range in which surface deviations are generally termed surface roughness (as opposed to surface contour). In addition to giving values of rms roughness, the SDF can be used to infer more specific surface and machining parameters such as tool feed rate, groove shape information and tool chatter. The SDF also provides an interesting way of comparing roughness measurements made by systems with different spatial frequency band widths. Results are given for a number of machined surfaces. The tendency for large amounts of low frequency roughness is discussed. Surface groove shape is shown to be different from the expected "circular cusp shape" calculated from tool radius and feed rate.
Diamond machining of materials for optical applications is becoming an important fabrication process. This report describes current development work in material-removal technology to better understand the mechanics of the diamond-turning process, its limitations, and applications. The technique is presently limited to a select group of metals, most of which are of a face-center-cubic crystal structure. Machinability studies were done which were designed to better understand diamond compatibility and thus expand the range of applicable materials. Nonconventional methods such as ultrasonic tool stimulation were investigated. Work done to determine the machinability of infrared window materials indicates that this is a viable fabrication technique for many materials, although additional effort is needed to optimize the process for particular materials.
Diamond turning is immediately applicable to the fabrication of infrared optical components because presently available machines can meet the reduced absolute accuracies required at 10 micrometers. An initial survey of infrared sensor programs at the Honeywell Radiation Center has been conducted to predict the near term and future demand for diamond turned optical components. Not only does the fabrication process promise significant cost savings as compared to conventional lapping and polishing methods, but, as in the case of aspheric lenses, wider applications are also sought to reduce weight and space requirements. In addition, broader usage of diamond turned aspherics reduces total parts count and assembly and alignment time, provided proper tools and test equipment are employed. The potential cost savings of diamond turned vs conventionally-fabricated optics are summarized for contracts at the Radiation Center. The savings were calculated by subtracting the difference in fabrication costs and multiplying by the number of items expected to be produced into the mid-1980's. Technical fall-out potential of the diamond turning process is also noted in the apparent ability of a coated sample to pass a 24-hour salt fog test.
The pantograph incorporates a diamond wheel spindle on a precision air bearing running with great smoothness and works at a ratio of 6-1 following a master cam which was made by tape control. The glass is held to the work spindle by vacuum. Roughing cuts are made with metal bond diamond wheels and finishing cuts with resin bond wheels. Surface accuracies of ±0.0001" per inch are obtainable along with a 5 micro inch surface roughness.
The X-ray astronomy group at Caltech has developed an X-ray telescope for sounding rocket-borne observations above the Earth's atmosphere. The telescope consists of a pair of nested aluminum mirrors, 40.64 cm and 31.65 cm in diameter with a total geometrical collecting area of 200 cm2. The mirror surfaces have been machined at the Y-12 plant of the Oak Ridge National Laboratory using an air bearing spindle lathe and a diamond tool. Design and performance characteristics will be presented. The design of the next generation telescope of 91 cm diameter will be presented.
Design techniques for Wolter grazing incidence x-ray microscopes are discussed, and considerations applicable to diamond point micro-machining fabrication are described. Also preliminary results of tests on a micro-machined mandrel replicated system are presented.
Diamond machining of non-ferrous and plastic optical components is drawing increasing interest as a method of producing both prototype and production optics economically and with lesser skill than historic polishing methods. Pneumo Precision, with a background in air bearing spindles, air bearing slides, and metrology has combined these technologies with diamond tools to introduce a commercial line of machine tools termed "Micro Surface Generators" specifically designed for diamond turning, flycutting, and grinding. This paper will present the findings of our research and development in diamond micro surface generation machines and will illustrate the range of application of this equipment. Included will be discussions and illustrations of diamond turning of surfaces of revolution; diamond fly-cutting of plano surfaces including multi-faceted scanners; and diamond grinding. The use of this equipment in a standard optical or precision machine shop setting rather than in a super laboratory environment will be discussed. Conclusions as to the future of diamond machining as a commonplace optical fabrication method will be presented.
The demand is increasing for the highly exact machines needed for the production of precise metallic reflectors. These machines have geometric motions which far exceed the the precision ordinarily accepted in machine tools. This paper selects one type of carriage motion as produced by one manufacturer. It then pin-points that particular "state of the art" to enable the user to specify and set a norm for expected performance.
The Machine Tool Industry, as a whole, has not been willing because of the generally "one-shot" nature of ultra-precision machine requirements, to enter this field of precision machines. However, as the accuracy trend of "standard" machine tools has always been toward lower tolerances, a point is reached where new systems and state of the art components must be evaluated for incorporation in a new line of equipment to meet these accuracy needs. Thus, the entry of Ex-Ce110 Corporation into the ultra-precision machining field was a direct effort to extend their present capability into an area that future requirements will lead, if the present trend toward higher accuracy continues. This paper presents some data on equipment availability, experiences, problems, manufacturing and inspection capabilities and future possibilities of ultra-precision machining systems.
We describe the set up and measurement techniques to evaluate a diamond turned 300 mm diameter copper toroid. A single beam interferometer, rotary table, and Moore measuring machine were used to measure the circular flatness of 0.63 μm (25 μ") and 30 nm (1.2 μ") rms figure deviation. A computer program was used to evaluate the figure and absolute average slope error of 12 μrad.