A very compact active x-ray mirror based on the properties of bimorph piezoelectric systems has been developed at the ESRF. The use of such a system as an x-ray focusing device has a number of advantages among which are compactness, low cost, and versatility. As a demonstrative test, a white focused beam of 35 μm has been obtained on an ESRF bending magnet beamline that corresponds to a demagnification of 1/18. A theoretical description of the system behavior is given, and compared with both finite element analysis and interferometric measurements. Examples of more advanced devices are discussed.

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It is shown that Lennard-Jones parameters are not g o d correlating factors; the implications of this fact on the type of interaction potential effective for energy transfer from highly excited molecules are discussed.We have demonstrated reverse saturable absorption of picosecond pulses at 532 nm using the organometallic tetramer cyclopentadienyliron carbonyl [ (C5H5)Fe(CO)], dissolved in methylene chloride. Time-resolved pumpprobe measurements and numerical simulations based on a five-level model indicate that reverse saturable absorption of ultrafast optical pulses is due to excited singlet absorption in this tetramer. We have determined the lifetime of the first excited singlet state to be 120 ps, and have measured a singlet excited-state capture cross-section of 8 X lo-'* cm2, twice that of the ground-state cross-section. In addition, we have placed bounds on the lifetime of the second excited singlet state and the branching ratio between the singlet and triplet systems.

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