Abstract

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.

© 2005 Optical Society of America

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Figures (6)

Fig. 1.
Fig. 1.

Digital photograph of the white light SC induced by focusing (a) 1.5 μm and (b) 800 nm pulses at 1.3 μJ using the 1x objective lens.

Fig. 2.
Fig. 2.

(a) Measured white light SC spectrum induced by focusing 1.5 μm pulses in the silica, (b) spectrum of the input pulse beam (without sample).

Fig. 3.
Fig. 3.

(a) Digital photograph of a typical white light interference fringe produced by focusing 4 μJ pulses at 1.5 μm inside the glass, (b) white light pattern created at 4 μJ with 800 nm pulses.

Fig. 4.
Fig. 4.

CCD images of the white light fringes (500 nm component) produced by a pair of filament for (a) single shot, (b) multi-shot irradiation (5000 pulses) of the silica with 7 μJ pulses at 1.5 μm, (c) two-dimensional line scans corresponding to the single and multi-shot irradiation images. The beam was focused in air very close to the input surface.

Fig. 5.
Fig. 5.

White light fringe images corresponding to those illustrated in Fig. 4 but now obtained with 800 nm pulses. The beam was focused in air very close to the input surface.

Fig. 6.
Fig. 6.

(a) Image of a pair of filament (500 nm component) formed by 7 μJ pulses at 1.5 μm, (b) image of a bunch of filaments produced at 34 μJ.

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