Hans K. Pew

Image Quality Of Figured Multilayered Optics

The reflectivity and resolution of a multilayer structure is strongly affected by the roughness at the interfaces between two successive layers and by the amount that the constituent materials will diffuse into one another at the interfaces. Performance is also affected by the variations in individual layer thicknesses and by inhomogeneities in the materials. These deviations from the ideal multilayer will also affect the quality of the image from a figured multilayer optical element. The theory used to model the effects of non-ideal multilayers on the image quality of figured optics will be discussed. The relationship between image quality and multilayer structure quality will be illustrated with several examples.

An XRD/XRF instrument for the microanalysis of rocks and minerals

A breadboard setup constructed at MOXTEK, Inc., is capable of capturing both x-ray diffraction (XRD) and x-ray fluorescence (XRF) information simultaneously using a charge-coupled device (CCD) as the x-ray detector. This preliminary setup will lead to a prototype simultaneous XRD/XRF instrument. NASA is funding the instruments construction because of its capabilities and small size; it could be used for future Mars missions for analysis of rocks. The instrument uses a CCD to capture both the energy and the spatial information of an incoming x-ray. This is possible because each pixel acts as a spatially addressable energy-dispersive detector. A powdered sample of material is placed in front of the CCD, which in turn is bombarded by a collimated x-ray beam. The instruments critical features - namely the x-ray source, collimation optics and x-ray transparent windows - allow for the first time, to the best of our knowledge, mounting the sample outside the CCD camera. In this paper the instruments design parameters as well as the properties of both a front-side-illuminated (FSI) CCD and back-side-illuminated (BSI) CCD as x-ray detectors are investigated.

Theoretical Considerations in the Design of Multilayer X-Ray Optics

There is increasing interest in the application of multilayers to figured x-ray optics. Two concepts in design approach are presented. The requirements for image formation with a multilayer device are discussed. A geometrical approach is used. The possible affect of multilayers on image quality are studied. Models for the reflectivity of x rays by multilayers are compared briefly.

Field emission x-ray tube for mammography

We propose to develop a time-gated x-ray imaging technique for screening mamography. If successful, it will greatly improve the accuracy of current mammography with about 50% reduction of current patient radiation. The technique can be applied to other x-ray imaging procedures also. We are now working to determine the feasibility of the key technologies- an x-ray source that can be pulsed on and off at a subnanosecond rate and a detector that can be gated at the same rate- that represent potential roadblocks to achieving this goal. A field emission x-ray tube will be used as the source. The field emission cathode consists of a substrate with sharp points and a metallic grid. A voltage on the grid creates an electric field that produces tunnel emission from the array of tips. The geometry of such a tube make electron optics easier, high currents are possible and the tube can be turned on and off rapidly. It also appears that synchronous electronic gating of the detector is possible.

Microstructural and chemical characterization of the inconel/Ti(N) thin film and multilayer system

Single layer and multilayer films of titanium and Inconel 600 (76 at.% Ni, 16 at.% Cr, 8 at.% Fe) have been prepared by sputtering in argon/nitrogen atmospheres, with nitrogen partial pressures ranging from 0% to 40%. The microstructure and chemistry of the sputtered films were characterized using transmission/high-resolution electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, electron probe microanalysis, and ion beam analysis with MeV helium beams. The microstructure depended on deposition power and individual layer thickness, as well as the sputtering atmosphere composition. Metal nitrides were formed in single layers of both materials whereas, for multilayers, nitrogen was preferentially incorporated into the titanium layer.

A Software Package For The Analysis Of General Multilayer Performance Data

In an effort to make data on the reflectivity and transmission of multilayer optical elements more usable, we have developed a computer code for the manipulation and graphical display of a general data set consisting of x, y, and delta-y values. The code was developed for a DEC VAX computer running a version 4.2 or later VMS operating system. Facilities are available for algebraic manipulation, editing, smoothing, interpolating, and deconvolving data sets in a straightforward way. The code is entirely self-contained with the exception of the graphics output support, which is centralized to allow for simple interfacing to the graphics package resident on the target system. The capabilities of the code are described and sample output is shown.