SBS management in Yb-fiber-amplifiers using multimode seeds and pulse-shaping.

We present a comprehensive analysis of the technique of Longitudinal-Mode-Filling (LMF) to reduce Stimulated Brillouin Scattering (SBS) limitations in Ytterbium Doped Fibre Amplifiers (YDFA), for the generation of nanosecond, temporally shaped pulses. A basic Master-Oscillator-Power-Amplifier (MOPA) system, comprising an output YDFA with 10 µm-core active fibre, is experienced for benchmarking purposes. Input pulse-shaping is operated thanks to direct current modulation in highly multimode laser-diode seeds, either based on the use of Distributed Feed-Back (DFB) or of a Fibre Bragg Grating (FBG). These seeds enable wavelength control. We verify the effectiveness of the combination of LMF, with appropriate mode spacing, in combination with natural chirp effects from the seed to control the SBS threshold in a broad range of output energies, from a few to some tens of µJ. These variations are discussed versus all the parameters of the laser system. In accordance with the proposal of a couple of basic principles and with the addition of gain saturation effects along the active fibre, we develop a full-vectorial numerical model. Fine fits between experimental results and theoretical expectations are demonstrated. The only limitation of the technique arises from broadband beating noise, which is analysed thanks to a simplified, but fully representative description to discuss the signal-to-noise ratio of the amplified pulses. This provides efficient tools for application to the design of robust and cost-effective MOPAs, aiming to the generation of finely shaped and energetic nanosecond pulses without the need for any additional electro-optics.

Demonstration of a true single-shot 100 GHz-bandwidth optical oscilloscope at 1053-1064 nm.

We demonstrate an innovating design to validate and to optimize the real-time performance of an all-optical oscilloscope at 1053-1064 nm. A unique broadband pulse is generated by means of frequency beats and of proper optical-shaping, which helps us to evidence a signal bandwidth of 100 GHz and a dynamics range in excess of 25 dB. Gain-narrowing and dispersion effects due to the replication of the input pulse are shown to be the first limitations in the broadband capabilities.

Generation of variable width pulses from an Yb(3+): YAG Integrated Dumper - Regenerative Amplifier.

We propose an original optical architecture for the construction of an Integrated Dumper - Regenerative Amplifier, by combining pulse generation and pulse slicing together with downstream regenerative amplification within a common amplifying unit and resonator. This design provides relatively short pulses at high energy, using a fairly simple and robust two-path resonator. The demonstration is performed with the help of a diode-pumped Yb(3+): YAG slab operated at room temperature at 1Hz PRF, in the energy range of 5 to 50mJ per pulse with 500ps to 5ns FWHM.

Theoretical design for the optimization of a material's geometry in diode-pumped high-energy Yb3+:YAG lasers and its experimental validation at 0.5-1 J.

The geometry of ytterbium-doped active media in diode-pumped lasers can be calculated with the help of a few analytic expressions for the optimization of high-energy and high-efficiency Q-switched lasers. The first step in the optimization consists in the definition of a basic three-level model with which to estimate the energy to be extracted. In the second step, for validation purposes we use a side-pumped Yb3+:YAG slab at 2-kW peak pump power in the long-pulse mode of operation up to 1 J, and we Q switch it at reduced energies up to 100 mJ. The final step of this study provides fairly general relationships devoted the geometric sizing of optimized slabs that will be of some interest for the design of higher-energy ytterbium-doped Q-switched lasers.