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Nouveaux concepts de sources lasers et paramétriques pour lidar à absorption différentielle

Abstract : The monitoring and control of greenhouse gas emissions on industrial sites is a major theme for the ecological transition. One approach to address this issue is to probe the gas concentration in plumes emitted by plants. A solution for the future is based on the development of a differential absorption lidar (DIAL) measuring instrument, which makes it possible to analyze the concentration and locate the emission of gas. In this context, ONERA is committed to the development of NesCOPO-type parametric sources, energetic and tunable in specific spectral bands.The deployment of such a technology in the field requires the development of a versatile, robust and very compact instrument. To achieve these objectives, the project will focus on the following points: versatility and robustness. As a first step, a study of the wavelength control of NesCOPO has been carried out. The aim was to choose the emission wavelength of the complementary wave of the OPO (around 3.3 µm), and to stabilize it by controlling the pump wavelength. It is the mixing of this complementary wave and another pump laser in optical parametric amplification (OPA) stages that made it possible to generate a wave around 1.5 µm. The wavelength tuning of the wave at 1.5 µm is obtained with the pump frequency of the OPA. This pump laser requires specific characteristics of tunability and energy. For this, we have chosen a MOPA architecture, with a tunable fiber laser as the injection source. A hybrid amplification architecture based on ytterbium doped fibers followed ytterbium bulk crystals allows us to obtain energies of several mJ. The fiber stages defines the temporal characteristics of the source (15 ns at 5 kHz). Limited by the stimulated Brillouin scattering, the energy rise is ensured by the bulk crystal-based amplification stages.Following this, OPA stages were set up, pumped by the tunable pump laser and injected by the complementary wave of the OPO. This signal wave from the OPA is then amplified by non-linear crystals positioned in cascades, delivering energy pulses in the order of hundred µJ. The wavelength tuning of this wave by the pump wavelength is characterized directly and by an absorption spectroscopy experiment with acetylene. This signal wave from the OPA was then amplified by non-linear crystals positioned in cascades, delivering pulses of the order of a hundred µJ.
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Thomas Hamoudi. Nouveaux concepts de sources lasers et paramétriques pour lidar à absorption différentielle. Optique [physics.optics]. Université Paris-Saclay, 2020. Français. ⟨NNT : 2020UPASP077⟩. ⟨tel-03191600⟩

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