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Ferrofluids can be used to make deformable mirrors having highly interesting characteristics (e.g., extremely large strokes and low costs). Until recently, such mirrors were thought to be restricted to corrections of frequencies lower than 10 Hz, thus limiting their usefulness. We present counterintuitive results that demonstrate that the limiting operational frequency can be increased by increasing the viscosity of the ferrofluid. We tested the response of ferrofluids having viscosities as high as 494 cP, finding that they could allow an adaptive optics correction frequency as high as 900 Hz. We also demonstrate that we can counter the amplitude loss due to the high viscosity by overdriving the actuators. The overdriving technique combines high current, short duration pulses with ordinary driving step functions to deform the mirror. The integration of a FDM in a complete closed-loop adaptive optics system running at about 500 Hz thus appears to be a realistic goal in the near future. OCIS codes: 220.1000, 220.1080, 230.3810.

We describe a new technology for the fabrication of inexpensive high-quality mirrors. We begin by chemically producing a large number of metallic nanoparticles coated with organic ligands. The particles are then spread on a liquid substrate where they self-assemble to give optical quality reflective surfaces. Since liquid surfaces can be modified by a variety of means (e.g., rotation, electromagnetic fields), this opens the possibility of making a new class of versatile and inexpensive optical elements that can have complex shapes and that can be modified within short time scales. Interferometric measurements show optical quality surfaces. We have obtained reflectivity curves that show 80% peak reflectivities. We are confident that we can improve the reflectivity curves because theoretical models predict higher values. We expect nanoengineered liquid mirrors to be useful for scientific and engineering applications. The technology is interesting for large optics, such as large rotating parabolic mirrors, because of its low cost. Furthermore, because the surfaces of ferrofluids can be shaped with magnetic fields, one can generate complex, time-varying surfaces that are difficult to make with conventional techniques. OCIS codes: 000.3110, 240.6700, 260.3910, 350.1260.

The photoexcitation, relaxation, and optical erasure regimes of spiropyran- (SP-) doped polymer films were studied. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices. We studied the character of the photoreaction for both coloring and bleaching processes. Reversible holographic recording in SP-PMMA films and the origin of the photochemical fatigue was studied upon repeated UV-visible irradiation cycles. [C] 2001 Optical Society of America