Self-guided propagation of ultrashort laser pulses in the anomalous dispersion region of transparent solids: a new regime of filamentation.

We report measurements concerning the propagation of femtosecond laser pulses in fused silica with a wavelength at 1.9 µm falling in the negative group velocity dispersion region. Under sub-GW excitation power, stable filaments are observed over several cm showing the emergence of nonspreading pulses both in space and time. At higher excitation powers, one observes first multiple pulse splitting followed by the emergence of the quasispatiotemporal solitary filament. These results are well reproduced by numerical simulations.

Characteristics of the Brillouin spectra in Erbium-Ytterbium fibers.

This paper reports the main characteristics of the Stokes spectra for typical pumped and unpumped Erbium-Ytterbium doped fibers. Doped fibers show shorter Brillouin shifts and their spectra are up to 1.6 times broader than undoped fibers. Those spectra are composed of several peaks originating from several longitudinal acoustic modes. The effective Brillouin gain of the secondary modes can be as large as 20% of the main peak gain. They can merge into a more complex structure for the largest cores. Simulations allow to relate these characteristics to the influence of codoping and index profile inhomogeneity. An additional broadening of the Stokes spectrum in pumped fibers is reported and attributed to thermal effects.