Abstract

The solid-density plasma formation has recently been a major concern since the advent of a high-intensity femtosecond laser.¹ It is attributed to contributions from both self-focusing from the intensity-dependent refractive index and self-defocusing resulting from ionization.² Although experiments for optical plasma formation and bulk modification in solids using high power femtosecond laser pulses have been reported,³ the variations of laser induced plasma formation and modification in a solid for input intensities have not yet been found clear. To understand the relationship between plasma formation and input intensity, a multimode optical fiber was used, in which the behavior of plasma formation for various input intensities was able to be studied in situ, easily instead of using bulk materials. In this paper, we report, for the first time to our knowledge, the experimental observation of laser induced solid-density plasma formation and bulk modification in a multimode optical fiber excited by a high intensity (above 10¹² W/cm²) femtosecond Ti: Sapphire laser.

© 1998 IEEE