AVS 47th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM11
Uranium Coated Optics for Space Applications in the Extreme Ultraviolet

Thursday, October 5, 2000, 11:40 am, Room 203

Session: Optical Films
Presenter: D.D. Allred, Brigham Young University
Authors: D.D. Allred, Brigham Young University
R.T. Turley, Brigham Young University
W.C. Cash, University of Colorado
M.B. Squires, Brigham Young University
D. Oliphant, Brigham Young University
Correspondent: Click to Email
We have developed a new family EUV multilayer mirror coatings using uranium. Using this approach we have coated a set of 6 mirrors for the EUV Imager, a component of the IMAGE mission. It will study the distribution of He + in the Earth's plasmasphere by detecting its resonantly scattered emission at 30.4 nm (41 eV). The 30.4 nm feature is, in principle, relatively easy to measure because it is the brightest ion emission in the plasmasphere, it is spectrally isolated and the background at that wavelength is negligible. There is, however, a bright emission at 58.4 nm (21 eV) light, which comes from neutral helium in the earth's ionosphere which also must be blocked. It is at too high an energy to filter with aluminum but at too low an energy to have negligible reflectance from most materials commonly used in EUV mirrors. Thus, a multilayer system which satisfied two optical functions: high reflectance (>20%) at 41 eV but low reflectance (<2%) at 21 eV were designed and fabricated. Such mirrors with such dual optical function in the soft x-ray/EUV have not previously been designed or built. These specifications were particularly challenging because many materials have higher single layer reflectances at 58.4 nm than at 30.4 nm. Essentially, the mirror must have low reflectance at 21 eV without loss of reflection at 30.4 nm. This was accomplished. The top part of the stack which reflects well at 30.4 nm acts as antireflection layers for the rest. For the flight mirrors we used the top uranium tarnish layer which naturally forms on such multilayers in a few seconds in air as an intrinsic part of achieving high 30.4 and low 58.4 nm reflectance. We will present data taken from the IMAGE satellite that demonstrates the implementation of the dual function multilayers using uranium. We will also discuss the other applications that we are developing that use uranium as a highly reflective mirror at 5 nm.