Observation of Self-Channeled Plasma Formation and Bulk Modification in Optical Fibers Using High-Intensity Femtosecond Laser

Abstract

We report the first experimental observation of laser-induced self-channeled plasma formation and bulk modification in multimode optical fibers during excitation by a high-intensity (more than 1011 W/cm2) femtosecond (110 fs) Ti: sapphire laser (780 nm). Solid-density plasma formation at various input intensities and the corresponding variation of anti-Stokes spectra were observed simultaneously. The threshold intensity for plasma formation in the optical fiber was found to be 8×1011 W/cm2. When the input intensity reached 1.5×1012 W/cm2, self-channeled plasma formation was observed at a distance of 9–10 mm from the input end of an optical fiber. After 5 min of irradiation at 1.7×1012 W/cm2, bulk modification, 5 µm in diameter and approximately 6 mm in length was observered in two types of multimode optical fibers with core/cladding diameters of 100/110 µm and 200/220 µm.