We study multiphoton absorption-induced damages to standard silica multimode optical fibers, induced by means of femtosecond infrared laser beams. During the damaging process, the dynamics of beam propagation turns out to non-trivially evolve over a time scale of several hours. Such a long term evolution produces an irreversible drop of the optical transmission, which is accompanied by a drastic change of the output supercontinuum spectrum. A microscopic analysis of the damages was carried out by means of both optical microscopy and absorption-contrast computed X-ray tomography. This has permitted us to obtain information about the sign of the refractive index variation which is induced by the optical breakdown. Our results will find application in a wide array of emerging technologies employing high-power fiber optic beams, such as fiber lasers and micromachining.
KEYWORDS: Electron beams, X-rays, Laser systems engineering, X-ray sources, S band, Monte Carlo methods, Optical simulations, Hard x-rays, X-ray imaging, Compton scattering, Particle accelerators
There is a strong demand for small foot-print high-flux hard X-rays machines in order to enable a large variety of science activities and serve a multidisciplinary user community. For this purpose, two compact Inverse Compton Sources (ICSs) are currently being developed in Italy. The most recent one is the Bright and Compact X-ray Source (BriXS) which has recently been proposed to produce very energetic X-rays (up to 180 keV) and high photon flux (up to 1013 photons/s with expected bandwidth of 1-10%). BriXS will be installed in Milan and it will enable advanced large area radiological imaging applications to be conducted with mono-chromatic X-rays, as well as allowing basic fundamental science of matter and health sciences at both pre- and clinical levels. Based on an energy-recovery linac (ERL) scheme and superconducting technology, BriXS will operate in CW regime with an unprecedented electron beam repetition rate of 100 MHz. The second Italian ICS light source is the Southern Europe Thomson back-scattering source for Applied Research (STAR) which is currently installed at the University of Calabria (UniCal). STAR is a compact machine that has been designed to produce monochromatic and tunable, ps-long, polarized X-ray beams in the range 40-140 keV with a photon flux up to 1010 photons/s and energy bandwidth below 10%. The electron beam injector is based on normal-conducting technology in S-Band with a repetition rate up to 100 Hz.
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