X-Message-Number: 13737 From: Date: Wed, 17 May 2000 07:53:52 EDT Subject: optical system in the X-ray domain X-ray optics. A lot of optical element is in order in a QND interferometer. There are "classical" lenses of the Fresnel kind limited to some millimeters in diameter. Making them at the nanometer scale precision is a challenge in itself. Other elements are even more uncommon, for example, elementary beams must be bunched side by side, that may be done with high incidence mirrors, something only possible with atom scale precision epitaxy. Then, outside the interferometer there must be a polarization filter, and a detector.The detector cells will be a kind of CCD with pixels in the ten micrometer range. This is 100 time the scale of the detected brain elements. An optical system must then enlarge the picture by this factor at the interferometer exit. Even if the elementary beams are first unbunched, the enlargement of a single 3 mm beam may need a one feet diameter mirror or lense. Because the optical precision of lenses are four time smaller than the mirror solution for a given result, lenses are *the* solution. Big X-ray lenses can't be built with the fresnel desing, the next best way is then to use the complex refractive index of many material in the X band to make a "classical" lense. Most material are strong absorber in the 1 keV domain of interest for QND interferometer, only solid hydrogen would be suitable. Making and keepping such a lens at some degrees above absolute zero is not a small undertaking in itself. Graphite could be a good alternative. It is carbon and carbon is not crystal clear at 1 KeV, but graphite is a crystal: all carbon atoms are keept in a stack of sheets. In two out of three directions, a polarized beaam may propagates without contact with the carbon atoms. That lens is at the same time a polarizer, by desing, it has some transparency only to vertical or horizontal polarization. This is not a problem here because we need indeed such a polarizer at the interferometer exit. Yvan Bozzonetti. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=13737