Double cladding structure in optical multimode fibers fabricated by a high-intensity femtosecond laser

To understand the relationship between solid-density plasma formation and input intensity, a multimode optical fiber was used, in which the behavior of plasma formation for various input intensities could be studied in situ. We report the experimental observation of laser induced long plasma formation and bulk modification in a multimode optical fiber excited by a high intensity (above 10/sup 12/ W/cm/sup 2/) femtosecond Ti:sapphire laser.