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Développement de lasers à fibres thulium bi-fréquences à impulsions synchrones pour la réalisation de sources Térahertz

Abstract : As part of a collaborative project between the XLIM laboratory (UMR 7252 of the CNRS and the University of Limoges) and the IPHT research laboratory located in Jena, Germany, my thesis project consists in the development of a widely tunable dual-wavelength synchronous pulsed thulium doped fiber laser for the realization of an efficient and tunable terahertz source. Based on the use of two volume Bragg gratings (VBGs) and a double-clad, polarization-maintaining thulium doped fiber (core diameter = 20 μm) manufactured by the REPUSIL method, a widely tunable single-wavelength laser and dual-wavelength laser has been realized and studied in continuous regime. A tunability of 1 nm to 144 nm was obtained with a power more than 4.5 W and a good signal-to-noise contrast (~ 45 dB) and a spectral linewidth less than 0.1 nm. In pulse regime, an acousto-optic modulator (AOM) was used in free space in the laser cavity to generate the pulses. The double-clad fiber has been replaced by a large-core thulium doped fiber (40 μm) called FA-LPF to to fend off the threshold of non-linear effects and work with a short fiber to decrease the pulse duration and increase the peak power of the obtained pulses. A widely tunable (from 3.8 nm to 120 nm) Q-switched dual-wavelength synchronous-pulsed thulium-doped fiber laser was developed with a peak power more than 8 kW and a pulse duration around 26 ns obtained independently of the value of Δλ at 1 kHz of repetition rate. A contrast higher than 20 dB was obtained limited by the FWM peaks generated for Δλ values below 45 nm. The spectral linewidth of the laser measured at 3 dB of the maximum was less than 0.3 nm.
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Mostafa Sabra. Développement de lasers à fibres thulium bi-fréquences à impulsions synchrones pour la réalisation de sources Térahertz. Optique / photonique. Université de Limoges, 2019. Français. ⟨NNT : 2019LIMO0118⟩. ⟨tel-02512463⟩

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