Petar Arsenovic

The Design, Implementation, and Performance of the Astro-H SXS Aperture Assembly and Blocking Filters

The calorimeter array of the JAXA Astro-H (renamed Hitomi) Soft X-ray Spectrometer (SXS) was designed to provide unprecedented spectral resolution of spatially extended cosmic x-ray sources and of all cosmic x-ray sources in the Fe-K band around 6 keV, enabling essential plasma diagnostics. The properties that make the SXS array a powerful x-ray spectrometer also make it sensitive to photons from the entire electromagnetic band, and particles as well. If characterized as a bolometer, it would have a noise equivalent power (NEP) of < 4x10-18 W/(Hz)0.5. Thus it was imperative to shield the detector from thermal radiation from the instrument and optical and UV photons from the sky. Additionally, it was necessary to shield the coldest stages of the instrument from the thermal radiation emanating from the warmer stages. Both of these needs are addressed by a series of five thin-film radiation-blocking filters, anchored to the nested temperature stages, that block long-wavelength radiation while minimizing x-ray attenuation. The aperture assembly is a system of barriers, baffles, filter carriers, and filter mounts that supports the filters and inhibits their potential contamination. The three outer filters also have been equipped with thermometers and heaters for decontamination. We present the requirements, design, implementation, and performance of the SXS aperture assembly and blocking filters.

Grating groove metrology and efficiency predictions from the soft x-ray to the far infrared

Methods for surface metrology have advanced significantly in the last few years, driven largely by the metrology needs for advanced lithographic processes. This paper applies recently developed metrology techniques to the specific problem of determining the groove structure of diffraction gratings well enough to reliably predict performance. Metrology devices used include an atomic force microscope, a contact profilometer, and a late-model optical microinterferometer. Examples of shallow (far-UV, high dispersion) and deep (IR echelle) gratings are presented, along with some conclusions of which metrology techniques are applicable for which types of diffraction grating. Also required along with the metrology is the use of fast, full electromagnetic model efficiency calculation codes which calculate the efficiency to be expected from a given mount, materials set, and grating profile. We present results qualifying codes we use against known and published results.

Nonlinear Elastic Characterization of Carbon Fibers

The non-linear elastic behavior of a series of pitch-based graphite fibers was studied using the method of laser generated ultrasound. A Q-switched Nd-YAG laser was used to produce pulses which generated stress waves in the fibers. The velocity of the acoustic wave was determined from the time of flight of the wave at the point of impact to a piezoelectric transducer positioned near one end of each specimen. The effective Youngs modulus of the fibers was determined for a wide range of static tensile stresses and varying temperatures. X-ray diffraction measurements were also made on these fibers, to determine such factors as crystallite size, orientation, and modulus. From these data, theoretical calculations of fiber modulus were performed, and the results compared to the ultrasonic modulus measurements. These results are useful for characterizing the elastic behavior of composites in which the fibers are used.

Automated Figuring and Polishing of Replication Mandrels for X-Ray Telescopes

In support of the Constellation X mission the Optics Branch at Goddard Space Flight Center is developing technology for precision figuring and polishing of mandrels used to produce replicated mirrors that will be used in X-Ray telescopes. Employing a specially built machine controlled in 2 axes by a computer, we are doing automated polishing/figuring of 15 cm long, 20 cm diameter cylindrical, conical and Wolter mandrels. A battery of tests allow us to fully characterize all important aspects of the mandrels, including surface figure and finish, mid-frequency errors, diameters and cone angle. Parts are currently being produced with surface roughnesses at the 0.4nm RMS level, and half-power diameter 0.6 arcseconds.

Telescopes for space-based gravitational wave missions

Abstract. Space-based observation of gravitational waves promises to enable the study of a rich variety of high energy astrophysical sources in the 0.0001 to 1 Hz band using signals complementary to traditional electromagnetic waves. Gravitational waves represent the first new tool for studying the sky since gamma ray telescopes debuted in the 1970s, and we expect compelling science to be the result. The fundamental measurement is to monitor the path length difference between pairs of freely falling test masses with laser interferometry to a precision of picometers over gigameter baselines. The test masses are arranged in an equilateral triangle to allow simultaneous measurement of both gravitational wave polarizations. The heliocentric orbital space environment enables the test masses to be shielded from large ground motions at low frequencies, and allows the construction of long measurement baselines that are well matched to the signal wavelengths. Optical telescopes play an important role in the measurement because they deliver laser light efficiently from one spacecraft to another. The telescopes are directly in the measurement path, so there are additional performance requirements to support precision metrology beyond the usual requirements for good image formation.

Constellation-X cylinder figuring and polishing studies

In support of Goddard Space Flight Centers (GSFC) Constellation-X mandrel manufacturing effort, a series of fabrication experiments are being performed to determine a best approach, and to supply the project with precision mandrels. Currently, polishing immediately after diamond turning produces a RMS surface roughness of 0.3 nm, on an electroless nickel-plated aluminum mandrel. Studies currently under way will incorporate an abrasive-figuring step to be followed by this polishing operation. The current diamond turning, figuring and polishing procedures will be described and the results presented.