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Metrology of reflection optics for synchrotron radiation

Description: Recent years have seen an almost explosive growth in the number of beam lines on new and existing synchrotron radiation facilities throughout the world. The need for optical components to utilize the unique characteristics of synchrotron radiation has increased accordingly. Unfortunately, the technology to manufacture and measure the large, smooth, exotic optical surfaces required to focus and steer the synchrotron radiation beam has not progressed as rapidly as the operational demands on these components. Most companies do not wish to become involved with a project that requires producing a single, very expensive, aspheric optic with surface roughness and figure tolerances that are beyond their capabilities to measure. This paper will review some of the experiences of the National Synchrotron Light Source in procuring grazing incidence optical components over the past several years. We will review the specification process - how it is related to the function of the optic, and how it relates to the metrology available during the manufacturing process and after delivery to the user's laboratory. We will also discuss practical aspects of our experience with new technologies, such as single point diamond turning of metal mirrors and the use of SiC as a mirror material. Recent advances in metrology instrumentation have the potential to move the measurement of surface figure and finish from the research laboratory into the optical shop, which should stimulate growth and interest in the manufacturing of optics to meet the needs of the synchrotron radiation user community.
Date: September 1, 1985
Creator: Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Evaluation of CVD silicon carbide for synchrotron radiation mirrors

Description: Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense x-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, and few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods.
Date: July 1, 1981
Creator: Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Understanding the performance of x-ray mirrors

Description: The manufacture of x-ray mirrors is a rather specialized branch of the optical fabrication industry. As those who have had to deal with the procurement of these components well know, there are only a handful of optical companies who supply most of the grazing incidence optics in use at the synchrotron light source facilities in this country. There is relatively little information available of practical use to guide the user through any of the above steps. We have been ''forced'' to develop our own foundation for assessing the performance of various vendors and determining the quality of the components produced by them. Our approach has been to concentrate on the area of metrology of grazing incidence optics and to develop instruments and techniques that can be used to improve the quality of components delivered to us. The major problem hindering the production of grazing incidence optics is the lack of specialized metrology instrumentation that can be used by the small manufacturing shop to assess the quality of the component under production. We have been engaged over the past several years in developing the theoretical framework and practical measurement techniques to link the metrology to actual performance, providing much-needed feedback to the manufacture and also educating users and manufacturers in the proper understanding of the language of surface figure and finish metrology.
Date: January 1, 1989
Creator: Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Statistical and signal-processing concepts in surface metrology

Description: This paper proposes the use of a simple two-scale model of surface roughness for testing and specifying the topographic figure and finish of synchrotron-radiation mirrors. In this approach the effects of figure and finish are described in terms of their slope distribution and power spectrum, respectively, which are then combined with the system point spread function to produce a composite image. The result can be used to predict mirror performance or to translate design requirements into manufacturing specifications. Pacing problems in this approach are the development of a practical long-trace slope-profiling instrument and realistic statistical models for figure and finish errors.
Date: March 1, 1986
Creator: Church, E.L. & Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Spectrometer system for investigation of biological molecules with synchrotron radiation at wavelengths greater than 125 nm

Description: The SUPERB experiment at the SURF II storage ring uses synchrotron radiation as a source of uv photons to measure circular dichroism (CD) of biological molecules. Conventional CD instruments are limited by the lack of stable laboratory continuum sources capable of providing large photon fluxes shortward of 200 nm. Synchrotron radiation overcomes these limitations and enables one to extend CD measurements down to the limit of the window transmission cutoff, which is 125 nm for CaF/sub 2/ used in the present configuration. Some molecules of biophysical interest, DNA and proteins for example, exhibit large CD effects below 200 nm, which reflect specific molecular conformations. CD is a sensitivie probe of molecular structure and enables us to learn how these molecules behave under various external conditions. In the future we plan to increase the measurement capabilities of SUPERB to include magnetic circular dichroism, fluorescence spectroscopy, and fluorescence lifetime measurements.
Date: April 1, 1980
Creator: Takacs, P.Z. & Sutherland, J.C.
Partner: UNT Libraries Government Documents Department

Silicon carbide mirrors for high power applications

Description: The advent of synchrotron radiation (SR) sources and high energy lasers (HEL) in recent years has brought about the need for optical materials that can withstand the harsh operating conditions in such devices. SR mirrors must be ultra-high vacuum compatible, must withstand intense x-ray irradiation without surface damage, must maintain surface figure under thermal loading and must be capable of being polished to an extremely smooth surface finish. Chemical vapor deposited (CVD) silicon carbide in combination with sintered substrate material meets these requirements and offers additional benefits as well. It is an extremely hard material and offers the possibility of being cleaned and recoated many times without degradation of the surface finish, thereby prolonging the lifetime of expensive optical components. It is an extremely strong material and offers the possibility of weight reduction over conventional mirror materials.
Date: November 1, 1981
Creator: Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Spectral and parameter estimation problems arising in the metrology of high performance mirror surfaces

Description: The accurate characterization of mirror surfaces requires the estimation of two-dimensional distribution functions and power spectra from trend-contaminated profile measurements. The rationale behind this, and our measurement and processing procedures, are described. The distinction between profile and area spectra is indicated, and since measurements often suggest inverse-power-law forms, a discussion of classical and fractal models of processes leading to these forms is included. 9 refs.
Date: April 1, 1986
Creator: Church, E.L. & Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Use of Diamond-Turned Mirrors for Synchrotron Radiation (SR)

Description: The diamond turning technique has great interest for users of synchrotron radiation because of its ability to produce surfaces of arbitrary shape. It also has the advantage of being well adapted to producing metal optics. These are of interest because they lend themselves to water cooling and hence represent one approach to the problem of high synchrotron radiation power loadings on optical surfaces. The optical figure produced by diamond turning is generally adequate for synchrotron radiation applications. The main difficulty centers around the question of smoothness. Diamond turned surfaces must receive a final polish after machining before they are sufficiently smooth for use with ultra-violet or x-ray radiation. The manufacturing stages can be carried out by various groups in the optics industry and the National Synchrotron Light Source has procured a considerable number of mirrors and is having them polished for use on the vuv storage ring. At the time of writing one mirror has been completed and evaluated and we give the results for this and discuss the indications for the future. The important measurement of the r.m.s. height of the surface roughness has given a value of 3 +- 0.9A using total integrated scatter of visible light at normal incidence.
Date: Summer 1981
Creator: Howells, M. R. & Takacs, P. Z.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation damage observations in normal incidence copper mirrors

Description: Water-cooled copper mirrors used at near-normal incidence on two beam lines at the NSLS are observed to undergo severe degradation upon exposure to the direct SR beam. These mirrors are used on beam lines designed to utilize radiation in the wavelength regions longer than 100 nm and are coated with a uv reflection-enhancing coating, consisting of one or more bilayers of aluminum with a MgF/sub 2/ overcoat. Beamline performance degrades very rapidly following installation of a new set of mirrors. Analysis of the mirror surfaces by various non-destructive techniques indicates severe degradation of the coating and surface along the central strip where most of the x-ray power is absorbed from the beam. In one case where the mirror had three bilayer coatings, the outer coating layer has disappeared along the central strip. Rutherford backscatter measurements indicate compositional changes between layers and confirm the existence of a carbon deposit on the surface. Thermal modeling suggests that most of the damage is caused by direct photon interaction, since the temperature rise in the energy deposition region is small.
Date: August 1, 1985
Creator: Takacs, P.Z.; Melendez, J. & Colbert, J.
Partner: UNT Libraries Government Documents Department

Grazing incidence synchrotron radiation optics: correlation of performance with metrology

Description: Image distortions produced by a cylinder mirror at the National Synchrotron Light Source are compared with performance predictions based on measurements of surface slope errors in the millimeter spatial period regime made with an optical surface profiler.
Date: June 1, 1986
Creator: Takacs, P.Z.; Hewitt, R.C. & Church, E.L.
Partner: UNT Libraries Government Documents Department

Application of silicon carbide to synchrotron-radiation mirrors

Description: Damage to conventional mirror materials exposed to the harsh synchrotron radiation (SR) environment has prompted the SR user community to search for more suitable materials. Next-generation insertion devices, with their attendant flux increases, will make the problem of mirror design even more difficult. A parallel effort in searching for better materials has been underway within the laser community for several years. The technology for dealing with high thermal loads is highly developed among laser manufacturers. Performance requirements for laser heat exchangers are remarkably similar to SR mirror requirements. We report on the application of laser heat exchanger technology to the solution of typical SR mirror design problems. The superior performance of silicon carbide for laser applications is illustrated by various material trades studies, and its superior performance for SR applications is illustrated by means of model calculations.
Date: September 1, 1983
Creator: Takacs, P.Z.; Hursman, T.L. & Williams, J.T.
Partner: UNT Libraries Government Documents Department

Significant improvements in long trace profiler measurement performance

Description: A Modifications made to the Long Trace Profiler (LTP II) system at the Advanced Photon Source at Argonne National Laboratory have significantly improved the accuracy and repeatability of the instrument The use of a Dove prism in the reference beam path corrects for phasing problems between mechanical efforts and thermally-induced system errors. A single reference correction now completely removes both error signals from the measured surface profile. The addition of a precision air conditioner keeps the temperature in the metrology enclosure constant to within {+-}0.1{degrees}C over a 24 hour period and has significantly improved the stability and repeatability of the system. We illustrate the performance improvements with several sets of measurements. The improved environmental control has reduced thermal drift error to about 0.75 microradian RMS over a 7.5 hour time period. Measurements made in the forward scan direction and the reverse scan direction differ by only about 0.5 microradian RMS over a 500mm, trace length. We are now able to put 1-sigma error bar of 0.3 microradian on an average of 10 slope profile measurements over a 500mm long trace length, and we are now able to put a 0.2 microradian error bar on an average of 10 measurements over a 200mm trace length. The corresponding 1-sigma height error bar for this measurement is 1.1 run.
Date: July 1, 1996
Creator: Takacs, P.Z. & Bresloff, C.J.
Partner: UNT Libraries Government Documents Department

NANOMETER PRECISION IN LARGE SURFACE PROFILOMETRY.

Description: The Long Trace Profiler (LTP) is in use at many synchrotron radiation (SR) laboratories throughout the world and by a number of manufacturers who specialize in fabricating grazing incidence mirrors for SR and x-ray telescope applications. Recent improvements in the design and operation of the LTP system have reduced the statistical error in slope profile measurement to the 1 standard deviation level of 0.3 microradian for 0.5 meter long mirrors. This corresponds to a height error on the order of 10-20 nanometers. This level of performance allows one to measure with confidence the absolute shape of large cylindrical aspheres and spheres that have kilometer radii of curvature in the axial direction. The LTP is versatile enough to make measurements of a mirror in the face up, sideways, and face down configurations. We will illustrate the versatility of the current version of the instrument, the LTP II, and present results from two new versions of the instrument: the in situ LTP (ISLTP) and the Vertical Scan LTP (VSLTP). Both of them are based on the penta prism LTP (ppLTP) principle that utilizes a stationary optical head and moving penta prism. The ISLTP is designed to measure the distortion of high heat load mirrors during actual operation in SR beam lines. The VSLTP is designed to measure the complete 3-dimensional shape of x-ray telescope cylinder mirrors and mandrels in a vertical configuration. Scans are done both in the axial direction and in the azimuthal direction.
Date: August 30, 1999
Creator: TAKACS,P.Z.
Partner: UNT Libraries Government Documents Department

SLOPE PROFILOMETRY OF GRAZING INCIDENCE OPTICS.

Description: Profiling instruments are well-suited to the measurement of grazing incidence optics, such as those found in synchrotron radiation beam lines. Slope measuring profilers, based upon the principle of the pencil beam interferometer, have proven to be especially useful in measuring the figure and slope errors on cylindrical aspheres. The Long Trace Profiler, in various configurations, is the most widely used of this class of profiler. Current performance provides slope measurement accuracy at the microradian level and height measurements accurate to 25 nm over 1 meter trace lengths.
Date: January 14, 2003
Creator: TAKACS,P.Z.
Partner: UNT Libraries Government Documents Department

Survey of surface roughness properties of synchrotron radiation optics

Description: Measurements of surface roughness were made on a large number of grazing incidence mirrors delivered for use at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The measurements were made with a WYKO optical profiler using a 2.5X and a 10X objective and analyzed with our PROFILE code to generate an average periodogram representation for each surface. The data is presented in the form of representative profiles with all of the periodogram curves arranged according to figure type. Analysis of the periodograms allows one to compute bandwidth-limited values for RMS roughness and slope, to provide valuable feedback information to manufacturers regarding compliance with specifications, and to predict the performance of the optic at x-ray wavelengths.
Date: March 1, 1986
Creator: Takacs, P.Z.; Colbert, J. & Church, E.L.
Partner: UNT Libraries Government Documents Department

Applications of the lateral shearing interferometer in measurement of synchrotron radiation optical elements

Description: The use of a single plate shearing, or Murty, interferometer for measuring the surface quality of several optical elements is reviewed and several results are given. The principle of the Murty interferometer is also explained. (LEW)
Date: November 1, 1987
Creator: Liu, Wu-ming; Takacs, P.Z. & Siddons, D.P.
Partner: UNT Libraries Government Documents Department

In-situ shearing interferometry of National Synchrotron Light Source mirrors

Description: In situ mirror distortion measurements were made with a lateral shearing interferometer on three mirrors in beam line X17T at the National Syn203hrotron Light Source. Lateral shearing interference is insensitive to vibrational motion in five of the six degrees of freedom, so it is well-suited for investigations in the synchrotron radiation (SR) environment. No distortion was seen in an uncooled silicon carbide mirror and in a colled copper alloy mirror on X17TB, but a change in the radius of an uncooled electroless nickel-plated aluminium cylinder mirror of about 6.2% was observed on X17TA. Angular vibrations in the 2 to 3 arc second range were easily observed on one of the beam lines, as was an overall mirror rotation in the arc second range.
Date: January 1, 1987
Creator: Qian, S.N.; Rarback, H.; Shu, D. & Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Figure and finish characterization of high performance metal mirrors

Description: Most metal mirrors currently used in synchrotron radiation (SR) beam lines to reflect soft x-rays are made of electroless nickel plate on an aluminum substrate. This material combination has allowed optical designers to incorporate exotic cylindrical aspheres into grazing incidence x-ray beam-handling systems by taking advantage of single-point diamond machining techniques. But the promise of high-quality electroless nickel surfaces has generally exceeded the performance. We will examine the evolution of electroless nickel surfaces through a study of the quality of mirrors delivered for use at the National Synchrotron Light Source over the past seven years. We have developed techniques to assess surface quality based on the measurement of surface roughness and figure errors with optical profiling instruments. It is instructive to see how the quality of the surface is related to the complexity of the machine operations required to produce it.
Date: October 1, 1991
Creator: Takacs, P. Z. & Church, E. L.
Partner: UNT Libraries Government Documents Department

Versatile spectrometer for experiments using synchrotron radiation at wavelengths greater than 100 nm

Description: The design of the SUPERB spectrometer places great emphasis on flexibility. Optics, electronics and the attendant computer system are of modular design and can be rapidly configured to perform a variety of tasks. This flexibility will permit SUPERB to perform the various experiments described above. Equally important, it should facilitate adaption of SUPERB to perform experiments the nature of which we are presently unaware.
Date: January 1, 1979
Creator: Sutherland, J.C.; Desmond, E.J. & Takacs, P.Z.
Partner: UNT Libraries Government Documents Department

Specification of the figure and finish of EUV mirrors in terms of performance requirements. Revision 11/94

Description: All manufacturing processes involve errors. In the case of bare and multilayer mirrors these unavoidable errors introduce near-field fluctuations in the reflected wavefront which propagate to the far field and degrade imaging performance. In order to specify manufacturing tolerances in terms of performance requirements we must know the connection between the two -- the finish-function relationship. This paper discusses the form of that relationship derived using elementary statistical diffraction theory. It tells us what statistical properties of the surface errors are relevant, it spells out the important role of the system parameters for EUV mirrors which is absent for conventional mirrors, and it leads to simple good-bad tests for mirror quality. These results are an extension of previous work in this area.
Date: November 1, 1994
Creator: Church, E. L. & Takacs, P. Z.
Partner: UNT Libraries Government Documents Department

Specifying the surface finish of x-ray mirrors

Description: Our measurements of x-ray mirrors at Brookhaven indicate that the power spectral densities of their finish errors have inverse power-law or fractal forms, rather than being flat at low frequencies as is usually assumed. This paper reviews these data and discusses how this apparent divergent behavior leads to finite but unconventional effects in imaging. Results are then used to develop more rational and realistic surface-finish specifications.
Date: December 31, 1993
Creator: Church, E. L. & Takacs, P. Z.
Partner: UNT Libraries Government Documents Department

BASIC program for power spectrum estimation. Revision

Description: A standard data set is presented to be used in testing routines that are developed for evaluating the one-dimensional periodogram spectral estimate of a series of uniformly spaced data points representing measurements of a surface profile. These data were generated using the GWBASIC program ``FFTPSD`` which is included in the Appendix of this report. The original purpose of this data set was to allow us to test and debug our own periodogram estimation routines, written in various programming, languages, against a standard data set. At the request of numerous individuals, we are making it available to others who may wish to do the same. We have also included a summary explanation of periodogram estimators and the various considerations that go into generating computer algorithms for power spectrum estimation.
Date: May 1, 1994
Creator: Church, E. L. & Takacs, P. Z.
Partner: UNT Libraries Government Documents Department