Machining of aspheres represents an extra field in the manufacturing of optical components. The deviation from the sphere has a big impact on machining and testing equipment, tools and technologies, achievable specifications and costs. The production of aspheres deals with special problems such as mid-spatial frequency errors, centering tolerances and slopes, not known in that degree from manufacturing of spheres. Over the past 20 years JENOPTIK Laser, Optik, Systeme GmbH has gained a wide experience of this application area. Recent results give a review on what is required to execute the transition from standard quality to high-precision aspheres, off-axis parts and free forms.
Computer generated holograms (CGH) are widely used in combination with standard Fizeau interferometers. The test of plane and spherical specimen is extended to the test of aspherical surfaces. The wave from a transmission flat or a transmission sphere is formed by the CGH to fit the surface of an asphere or a cylinder. There are some considerations for an advantageous design of this additional optical element in the beam path. The availability of a suitably designed CGH is often the limitation for the manufacturing of precision aspheres. JENOPTIK Laser, Optik, Systeme GmbH can provide a custom made CGH within a short time. We will show the design principles and the layout of the CGHs. The optical properties and the known limitations will be presented based on measurements of aspherical surfaces.
Off-axis paraboloids provide sophisticated challenges in both machining and measuring. There are 2 accepted approaches for manufacturing off-axis paraboloids. In method one, a rotationally symmetrical part is shaped and polished with subsequent separating the off-axis elements from the block. On the other hand, one can machine the single parts right from the start. In this case the surface is kind of free-form. In this paper we report on the manufacturing of mirrors for both methods. Special attention is paid to machining and measuring. The fabrication process consists of iteration steps. The polishing step can remove the remaining shape error of the mirror surface itself or the wave front of the system.
With computer generated holograms (CGH) the testing possibilities of interferometers for plane and spherical specimen is widened to the test of aspherical surfaces. The wave from a transmission flat or a transmission sphere is formed by the CGH to fit the surface of an asphere or a cylinder. The availability of suitable CGHs is often the limitation for the production of precision aspheres. JENOPTIK L.O.S. can provide a custom made CGH within a short time. We will show the design principles and the layout of the CGHs. The optical properties and the known limitations will be presented on the basis of measurements of aspherical surfaces.
JENOPTIK Laser, Optik, Systeme GmbH (JO L.O.S.) enlarged its product range in the field of cylinder lenses and crystal optics. These components are used in optical measuring technology and in various laser applications. The new cylinder components are a result of the state of the art manufacturing technology. For applications, where the quality of standard cylinders with a surface deviation of PV~Lambda/2 to ~Lambda/5 @632,8nm and tested with a reference glass only is not sufficient, the surface shape can be improved to PV Lambda/10 @632,8nm.
The presentation deals with Jenoptik's current state to produce cylinder optics, to reduce remaining surface shape deviations of semi-finished cylinder optics and to test these elements. Based on in-house developed machinery, cylinders are manufactured by means of blocking or drum. The required surface quality in the range of PV~Lambda/10 @632,8nm for cylindrical lenses can be reached by computer aided correction using mrf-polishing techniques in connection with an interferometer test set-up. Therefore, the polishing machine is equipped with an additional axis of movement. The interferometer measurement of the residual surface deviation is done by Computer Generated Holograms (CGH), which are designed and manufactured in-house. CGHs from JO L.O.S. for testing cylindrical lenses can be custom designed starting with F#1.0. They are related to the typical rectangular geometry of cylinder components. Using these measurement techniques, testing is no longer the limiting factor in achieving high quality cylindrical surfaces.
JO L.O.S. has all the capabilities of effective manufacturing, testing and correcting cylindrical lenses. Latest results achieved in series production are shown.
The paper deals with challenges, solutions and results obtained by JENOPTIK Laser.Optik.Systeme GmbH (JO L.O.S.) while contriving and transferring knowledge gained in the field of manufacturing and testing high-end spherical and plan surfaces into manufacturing of complex optical surface shapes. During the last two years notable progress was made in the field of manufacturing optical components with constantly changing curvature and lack of symmetry by linking selected manufacturing equipment and testing methods to each other. We will show present results reached in industrial manufacturing of complex surface shapes on an accepted level of expanse.
A small distinction of some micron makes an awful difference between spheres and aspheres. It takes special technological equipment to manufacture and test aspheric optics. This equipment is clearly distinguished from that for classical optics manufacturing. This paper deals with equipment installed at JENOPTIK L.O.S. and give results based on serial manufacturing of aspheres.
The cylinder geometry allows for grazing incidence tests of optical surfaces let it be micro- or macro cylinder lenses. By using diffractive beam splitter and beam shaping elements a grazing incidence interferometer can be built where the zero diffraction order is used as reference beam and one of the first orders as probe beam for the cylinder surface. Circular as well as noncircular meridian curves can be dealt with by shaping the DOE structure accordingly. The structure of the DOE are parallel curves to the meridian providing a constant spatial frequency which alleviates the lithographic process. The fringes indicate surface deviations from fringe to fringe by p/2 where p is the pitch of the DOE. A description of a micro- and a macro-interferometer together with measuring results will be given.
Increasing demands for accuracy in manufacturing and international standards of quality control require faster and more precise measurement techniques. Surface inspection and shape control of technical workpieces is commonly done by tactile profilometers. Interferometric testing of optically rough surfaces is faster, but the interference pattern is usually disturbed by high contrast speckle noise. Grazing incidence interferometry is an appropriate method to increase the effective illuminating wavelength. This leads to dramatically reduced speckle noise. Increasing of the wavelength from the visible to the infrared region is another opportunity to diminish speckle. An interferometric set-up combining both methods is presented. Well collimated laser light is splitted into several diffraction orders by a computer generated hologram (CGH). The zero diffraction order passes through to a second CGH and is used as the reference wavefront. The first diffraction order hits the object and is reflected to the second CGH where it is recombined with the reference wave. In the ideal case only uniform intensity is observed. Deviations from the ideal shape and misalignments of the object in the set-up lead to interference fringes after the second CGH. The fringe pattern is evaluated by using phase shifting interferometry. Further data processing eliminates the misalignment errors and reconstructs the shape of the object. The sensitivity of the interferometer depends on the design of the CGHs and can be adapted in a wide range to technical needs. The use of infrared light expands the measurement range. Rough surfaces can be tested with a convenient resolution in the direction of the optical axis. The capability of the IR-interferometer will be shown with some measurements of cylindrical workpieces.
The test of rod-like technical objects can be carried out in grazing incident using diffractive optical elements as beam splitters and at the same time as generators for master wave fronts. The occurring interference patterns can be evaluated with the help of the well known phase shifting technique. Wave aberrations caused by the adjustment state of the test sample can be removed from the data set via least squares fitting a functional representing the wave aberrations due to misalignments.
Interferometric testing of technical, optically rough surfaces is disturbed by high contrast speckle noise. Grazing incidence interferometry is an appropriate tool to increase the effective illuminating wavelength. This leads to dramatically reduced speckle noise. Increasing of the wavelength from the visible region to the infrared is another opportunity to diminish speckle. An IR-interferometric combining both methods is presented. The advantage of the IR-interferometer compared to the VIS-interferometer is the reduced anamorphotic distortion of the image, which increases the resolution in the z-direction of the cylinder and enables the measurement of rougher surfaces. The interferometric set-up consists of two diffractive axicons with the test piece in between. The axicons serve as references for the cylindrical test samples and as beam splitters and combiners. The plane wave of the 0- th diffraction order is the reference beam whereas the conical wave of the first order is deflected onto the object. After reflection from the cylindrical test sample the first order contains wavefront deformations due to deviations of the test sample from cylindricity. After recombination of the object and the reference beam by the second axicon a low frequency interference pattern is detected by a high resolution PtSi focal plane array. The surface deviations can be reconstructed with the methods of phase shift interferometry.
Increasing demands for accuracy in manufacturing and international standards of quality control require faster and more precise measurement techniques. Surface inspection and shape control of technical workpieces is commonly done by tactile profilometers. A faster alternative to this mechanical tool can be realized interferometrically. Grazing incidence of laser light onto the technical surface reduces speckle-noise significantly. In our setup computer generated holograms are used both as references for the technical surfaces to be tested and as beam splitter or recombing element. Each class of workpieces requires specific computer generate holograms, e.g. phase-gratings for plane surfaces or diffractive axicons for cylindrical and conical surfaces An ideally shaped workpiece will result in a zero fringe field. Deviations from the ideal shape will be indicated by interference fringes and fringe distortions. The sensitivity of the interferometer can be adapted to technical needs. The surface deviations of the workpiece are superimposed by adjustment aberrations which can be described mathematically with sufficient accuracy and eliminated by a least square fit. We will demonstrate this measurement technique with workpieces of different shape.
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