Multiphoton absorption of self-channeling and bulk modification in optical fibers using a high intensity femtosecond laser

For efficient fabrication of three-dimensional modification structures in transparent materials, the variation of nonlinear phenomena, i.e., plasma formation and modification by the n-th order multiphoton absorption, must be determined. In our experiment, a multimode optical fiber was used, which enabled us to study the process of plasma formation simultaneously at various input intensities, instead of bulk material. In this paper, we report the first experimental observation of three photon and six photon absorption process for self-channeling and bulk modification in multimode optical fibers during excitation by a high-intensity femtosecond Ti:sapphire laser