Improvements in the accuracy and the repeatability of long trace profiler measurements.

Modifications of the long trace profiler at the Advanced Photon Source at Argonne National Laboratory have significantly improved its accuracy and repeatability for measuring the figure of large flat and long-radius mirrors. Use of a Dove prism in the reference beam path corrects phasing problems between mechanical errors and thermally induced system errors. A single reference correction now completely removes both of these 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-h period and has significantly improved the stability and the repeatability of the measurements. Long-radius surface curvatures can now be measured absolutely with a high degree of confidence. These improved capabilities are illustrated with a series of measurements of a 500-mm-long mirror with a 5-km radius of curvature. The standard deviation in the average of ten slope profile scans is 0.3 microrad, and the corresponding standard deviation in the height error is 4.6 nm.

Surface roughness and scattering: papers from the first topical meeting.

This is an introduction to the feature on surface roughness and scattering.

Specification of surface figure and finish in terms of system performance.

We describe methods of predicting the degradation of the performance of a simple imaging system in terms of the statistics of the shape errors of the focusing element and, conversely, of specifying those statistics in terms of requirements on image quality. Results are illustrated for normal-incidence, x-ray mirrors with figure errors plus conventional and/or fractal finish errors. It is emphasized that the imaging properties of a surface with fractal errors are well behaved even though fractal-power spectra diverge at low spatial frequencies.

Optical constants for thin films of C, diamond, Al, Si, and CVD SIC from 24 A to 1216 A.

A method for deriving optical constants from reflectance vs angle of incidence measurements using a nonlinear least-squares curve-fitting technique based on the chi(2) test of fit is presented and used to derive optical constants for several thin-film materials. The curve-fitting technique incorporates independently measured values for the film surface roughness, film thickness, and incident beam polarization. The technique also provides a direct method for estimating probable errors in the derived optical constants. Data are presented from 24 A to 1216 A for thin-film samples of C, synthetic diamond, Al, Si, and CVD SiC. Auger electron spectroscopy depth profiling measurements were performed on some of the samples to characterize sample composition including oxidation and contamination.

X-ray and optical profiler analysis of electroformed x-ray optics.

Electroformed grazing incidence mirrors were tested with x rays and were measured with an optical profiler. Their total effective areas are ?70% of the theoretical values both for 1.5- and 6.4-keV x rays. The half-power diameters (HPDs) are ?2 min of arc at 1.5 keV. Comparing the x-ray test result with the optical measurement, we set requirements of high-frequency roughness <14 A and a midfrequency roughness <70 A for a HPD <1.5 min of arc at 7 keV. We also present a design of the mirror array telescope for high energies (MARTHE) which has a total effective area of ~1000 cm(2) for 7- keV x rays.

Electroformed grazing incidence x-ray mirrors for a mirror array telescope.

Grazing incidence Wolter type I mirrors for higher-energy x rays have been replicated from two superpolished mandrels by electroforming. Single mirrors and a nested pair were tested with 1.5- and 6.4-keV x rays, and their subminute of arc resolution and reflectivity close to the theoretical values are confirmed. We present the design of the mandrels, mirror mounting scheme, and results of the x-ray test. The microroughnesses of the mirrors measured using an optical profilometer were compared with the x-ray test results.

Z-DNA: vacuum ultraviolet circular dichroism.

In concentrated salt or ethanolic solutions, the self-complementary copolymer poly(dG-dC).poly(dG-dC) forms a left-handed double-helical structure that has been termed "Z-DNA." The first evidence for this structure came from changes observed in the circular dichroism (CD) spectrum between 230 and 300 nm for low- and high-salt solutions (Pohl, F. M. & Jovin, T. M. (1972) J. Mol. Biol. 67, 675-696). In 3 M NaCl, the CD spectrum is approximately inverted compared to the B-form spectrum observed in low-salt solution. We measured the vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) down to 180 nm under conditions in which the 230- to 300-nm spectrum is inverted. Below 200 nm, where the B form exhibits the large positive peak at 187 nm that is characteristic of right-handed double-helical DNAs, the Z form exhibits a large negative peak at 194 nm and a positive band below 186 nm. Therefore, the Z-form vacuum ultraviolet CD spectrum resembles an inverted and red-shifted B-form spectrum. The magnitudes of the differences observed between the B and Z forms in the CD spectrum below 200 nm are about 10 times greater than those observed between 230 and 300 nm. The vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) in 3 M Cs2SO4 also is inverted compared to the B-form spectrum; however, between 230 and 300 nm, it is nonconservative with a negative maximum at 290 nm and a weak positive CD signal above 300 nm, presumably reflecting differential light scattering and indicating the existence of molecular aggregates. Our results suggest that the vacuum ultraviolet CD spectrum is sensitive to the handedness of double-helical DNA structures. The CD spectrum in this region should complement other spectroscopic methods in relating the structures of poly(dG-dC).poly(dG-dC) existing in solution to those determined in the solid state by x-ray crystallography.

Extreme ultraviolet observations from voyager 2 encounter with jupiter.

Extreme ultraviolet spectral observations of the Jovian planetary system made during the Voyager 2 encounter have extended our knowledge of many of the phenomena and physical processes discovered by the Voyager 1 ultraviolet spectrometer. In the 4 months between encounters, the radiation from Io's plasma torus has increased in intensity by a factor of about 2. This change was accompanied by a decrease in plasma temperature of about 30 percent. The high-latitude auroral zones have been positively associated with the magnetic projection of the plasma torus onto the planet. Emission in molecular hydrogen bands has been detected from the equatorial regions of Jupiter, indicating planetwide electron precipitation. Hydrogen Lyman alpha from the dark side of the planet has been measured at an intensity of about 1 kilorayleigh. An observation of the occultation of alpha Leonis by Jupiter was carried out successfully and the data are being analyzed in detail.

Extreme ultraviolet observations from voyager 1 encounter with jupiter.

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S III, S IV, and O III indicating an electron temperature of 10(5) K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (>/= 1000 K) wvith a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Rocket ultraviolet spectrophotometry of comet kohoutek (1973f).

Observations of Comet Kohoutek (1973f) in the spectral region between 1200 and 3200 angstroms were made from an Aerobee rocket on 5.1 January 1974 universal time. The strongest features observed were the Lyman alpha line of neutral atomic hydrogen at 1216 angstroms and the hydroxyl (OH) bands at 3090 and 3142 angstroms. Atomic oxygen and atomic carbon were also detected, and their luminosity implies a production rate (of carbon monoxide or carbon dioxide) commensurate with that of water vapor.