We propose and demonstrate a pulse compression technique using a hollow fiber with a pressure gradient. This technique improves the spatial and spectral qualities of femtosecond laser pulses spectrally broadened by self-phase modulation, and allows an increase of the pulse energy for pulse compression. Using chirped mirrors for dispersion compensation, we have successfully compressed the pulse to less than 10 fs with an energy as high as 5 mJ.

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The propagation dynamics of intense femtosecond laser pulses in argon have been investigated theoretically and the results are compared with experimental data. It was found that in the initial stage the pulse propagates with the focal point moving ahead of the original one. The central beam of the trailing part experiences defocusing owing to ionization by the leading part and then regains self-focusing provided by power from the outer part. On propagating further, a quasistable balance is established between self-focusing and defocusing due to ionization-induced nonlinearity and diffraction, causing the beam to propagate in a self-guided mode. Furthermore, it was shown that the front of the split pulse decays faster, while the trailing edge experiences self-focusing and self-defocusing until a self-guided propagation mode is achieved. Multiple pulse splitting and shortening as a result of the dynamics near the focal point were also observed.

A new type of AFM tip characterizer used for characterizing nanostructures in the 10 nm to 100 nm range was developed. The characterizer was fabricated by preferential etching the edge of a cross sectioned Si/SiO 2 multilayer. Both isolated line structures and line-and-space structures were fabricated. The structural and practical properties of the fabricated tip characterizer were evaluated, and it was shown that it can be used to characterize AFM tip shapes in the 10 nm to 100 nm range.