Amplification d'impulsions brèves de haute énergie par effet Raman stimulé dans les fibres optiques

Authors: Hardy, Maxime
Advisor: Piché, MichelOlivier, Michel
Abstract: The development in the last decades of mode-locked fiber lasers resulted in the availability of reliable sources of femtosecond pulses that are both used for fundamental research and commercial applications. The wide gain bandwidth and excellent heat dissipation of rareearth-doped optical fibers have made possible the amplification and generation of high-energy ultrashort pulses with high repetition rates. However, phenomena such as nonlinear effects due to the small size of the beam and saturation of the population inversion in the gain medium tend to complicate their use for the amplification of pulses to energies exceeding the millijoule. Several strategies such as stretching the pulses to durations over the nanosecond, using photonic crystal fibers that have a wider core and parallelization have been used to circumvent these limitations, leading to pulses of a few millijoules with durations lower than a picosecond. This master’s thesis presents a novel approach for amplification of ultrashort pulses using stimulated Raman scattering in silica fibers as a gain mechanism. It is well known that this nonlinear effect allows the amplification with a wide bandwidth, such that it is nowadays commonly used in optical-fiber telecommunication networks. Because the adaptation of existing Raman amplification schemes to high-energy ultrashort pulses is not straightforward, we propose instead to transfer energy from a quasi-monochromatic pump pulse to a copropagating ultrashort signal pulse, stretched to comparable durations with a frequency chirp. In order to evaluate the potential of the Raman gain for the amplification of ultrashort pulses, this thesis presents an analytical model allowing the prediction of the amplified pulse’s features, depending upon those of the pump and upon the medium in which they are propagated. We thus find that the wide bandwidth of the Raman gain in silica glass, in addition to its inhomogeneous saturation, allows the amplification of signal pulses to energies of the same magnitude than that of the pump, while keeping their spectrum wide enough to support their compression to ultrashort durations. A few variants of the amplification scheme are presented, and their potential is evaluated using the analytical model or numerical simulations. We predict analytically and numerically the Raman amplification of pulses to energies of a few millijoules, whose durations are lower than 150 fs and having peak powers close to 20 GW.
Document Type: Mémoire de maîtrise
Issue Date: 2016
Open Access Date: 24 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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