Single crystal silicon has become readily obtainable and relatively inexpensive as a result of the production facilities set up to serve the semiconductor industry. It also has desirable properties for x-ray mirrors; it can be polished to a high degree of smoothness, has good mechanical properties, and high thermal conductivity. Polycrystalline silicon, which has greater mechanical strength, is also available. For these reasons we have used silicon mirrors exclusively at two bending magnet beamlines and one undulator beamline at the Advanced Light Source. We describe here two implementations of silicon mirrors: (1) a fixed radius design for high heat loads, which is side cooled by contacting to a water cooled block with Ga-In eutectic, and (2) designs in which a variable radius and/or an elliptical mirror figure are achieved by elastically bending a flat strip of the appropriate cross-sectional profile. Computed and measured performance figures are presented for each case.
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