Femtosecond pulses, adaptive control, fibers and photonic crystal fibers Fiorenzo Omenetto Mat'ls Science & Technology Div. Los Alamos Nat'l Lab. The implications of observing and mastering the nonlinear interaction between ultrafast pulses and optical fibers or photonic crystal fibers (PCF) is rich for both basic and applied science. Principally, when dealing with ultrafast pulses, it is essential to be able to characterize them in detail, to alter their shape to suit an experimental need and to ultimately use the information gathered to guide the experiment towards a desired solution. In short it is essential to observe, manipulate and control femtosecond pulses. In this talk, an attempt is made to address the approaches which have dealt with these three issues in the context of ultrafast (femtosecond) pulse propagation in optical fibers and PCFs. Experimental results on phase sensitive measurement techniques, femtosecond pulse shaping, and adaptive feedback control will be presented. Ultrafast pulse propagation in photonic crystal fibers will be illustrated, given the extreme interest in these new structures and their promise of being a crucial component of fiber-based systems and new devices.