We report on the observation of efficient and ultra-broadband white light super-continuum generated by focusing femtosecond pulses from an optical parametric amplifier at 1.5 μm in silica glass. The characteristic white light spectrum is extending from 400 nm up to at least 1750 nm. At sufficiently high input powers stable white light patterns associated with the interference of spatially coherent filamentary sources were observed and analyzed. Unlike focusing with 800 nm pulses from a Ti-sapphire laser, the stable fringes formed for each spectral component were pronounced owing to significantly reduced destructive impact of optical breakdown on filamentation of femtosecond pulses at 1.5 μm. By taking advantage of this property, the formation of optical waveguides in silica glass with considerably broader range of writing parameters as compared to those fabricated with 800 nm pulses, was demonstrated.
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