21 Septembre – Thesis defense - Gilles Dalla-Barba

14 h Amphi - Institut d'Optique d'Aquitaine (Talence)

Architecture of frequency domain optical parametric amplifier for generation of intense mid-infrared few-cycle laser pulses.

Last decades, emergence of intense Titanium:sapphire (Ti:Sa) lasers CEP-stabilized (career- envelope phase) has allowed the measurement of ultrafast phenomena for attosecond physics. Thanks to high-harmonic generation (HHG), a process predicted by the three steps model in 1993, attosecond pulses can be emitted and used for scanning the temporal dynamics of electrons in matter. Due to the quadratic dependance of the driving laser wavelength on the electron ponderomotive energy during HHG process, scientists are now looking forward a new generation of intense coherent sources in the mid-infrared (MIR) domain, a little covered range of wavelengths in which amplifier media are still lacking.
In the first part of this thesis, an architecture of optical parametric amplification (OPA) in frequency domain is presented to produce MIR intense field from a terawatt Ti:Sa laser. This MIR source, tunable from 5.5 μm to 13 μm and CEP-stable, has been characterized in the temporal domain by a pump-probe technique developed by laboratories of University of Bor- deaux (France) and Institut national de la recherche scientifique (Canada), before being used for driving a HHG experiment in solids, a phenomena discovered in 2011. A second architec- ture of OPA is also presented to generate intense field rather near 3 μm, based on a difference frequency generation (DFG) in frequency domain.
To this day, the generation of intense MIR radiation is hindered by the low conversion ef- ficiency of photons from near-infrared (NIR) to mid-infrared, restricting attosecond science to very costly multi-terawatts titanium:Sapphire facilities. However, innovations in Thulium and Hol- mium technologies over the last decade has intended 2 μm lasers to become a viable solution for pumping MIR OPA. The second part of this manuscript is dedicated to the development of new amplifier media made of Holmium-doped ceramics. Thanks to a fast and cost-effective pro- duction process and the possibility to realize inhomogeneous chemical compositions, ceramics show some advantages compared to monocrystals. In this context, Holmium-doped ceramics have been fabricated by a partner university and an innovative method is presented here to study and characterize optical losses and emission processes in these materials, with the am- bition of equaling, even exceeding, optical performances of monocrystals.

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