06 Décembre – Thesis defense - Giuseppe Scurria

10 h Room Schardin - French-German Research Institute of Saint-Louis

High power 2 µm fiber laser for mid-infrared supercontinuum generation in fluoride fibers.

High brightness and broad spectrum optical sources in the mid-infrared (mid-IR) are promising for different applications such as optronic countermeasures, LIDAR systems and spectroscopy. This thesis research work is dedicated to the investigation of high power supercontinuum generation in the 2-5 µm range. A thulium-doped ber laser emitting at 2 µm has been built and characterized in continuous wave, Q-switching and Q-switched mode-locking regime. In continuous wave operation, as much as 45 W have been reached with a slope e ciency of 58%. The implementation of two fused-quartz endcaps fusion spliced at the extremities of the active-fiber improved the thermal management and the overall stability of the entire system in all mentioned regimes of operation, allowing for higher pump powers. In Q-switched mode-locking, the maximum average output power level was 40 W, for a Q-switch
repetition rate of 150 kHz. At the average output power level of 20 W and 50 kHz of Q-switch repetition rate, the most energetic mode-locked pulse had an energy of 88 µJ and an estimated peak power of 60 kW. In all the mentioned operation regimes, the measured beam parameter M2 of the fiber laser was 1.1, close to the diffraction limit. This laser has been used to pump fluoride optical fibers (ZBLAN and InF3) for supercontinuum generation in the 2-5 µm range. In ZBLAN, more than 10 W in all spectral bands have been obtained, with an output spectrum extending up to 4.4 µm. A conversion efficiency of 35%/28%/15%/8% has been measured for wavelengths longer than 2.15 µm/2.65 µm/3.1 µm/3.5 µm, respectively. For the InF3 ber, a new design of an injection system, consisting of a large core diameter ZBLAN optical fiber and a commercial fiber-to-fiber coupler, allowed to enhance the thermo-mechanical stability of the fiber. The supercontinuum radiation generated in InF3 showed an output spectrum spanning up to around 4.7 µm with an output power level of 7 W in all spectral bands.
To the best of our knowledge, this was the first Watt-level supercontinuum radiation in an InF3 fiber pumped by a single-oscillator.

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