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Montée en brillance des réseaux de lasers à fibre : Nouvelle approche par diagnostic à contraste de phase dans une boucle d’optimisation

Abstract : Coherent laser beam combining techniques rapidly appeared highly promising in the field of ultra-high power laser sources. Indeed, the combined intensity around the propagation axis follows a quadratic law with the number of combined emitters. The first part of my work has been focused on passive phasing techniques, based on self-organization properties of coupled lasers. We have shown, both numerically and experimentally, that the intracavity filtering function due to the interferometric nature of the set-up, is an intrinsic reason for combining efficiency decrease far above laser threshold. The decrease goes steeper when the number of combined laser increases, making that kind of system inappropriate for coherently combining a large number of lasers delivering high power. The second part of my work consisted in studying an innovative active phasing method that associates a phase-contrast like filter with an optimization algorithm reducing phase errors between emitters. Both simulations and experiments showed the weak sensitivity of this method to the number of combined emitters. We demonstrated the phasing of 7 to 37 fiber lasers, delivering up to 5W each. To the best of our knowledge, this last result is the highest number of fiber lasers combined with an active phasing method. The combining efficiency has been estimated around 94%, corresponding to a residual phase error of λ/25. The weak number of algorithm iterations needed to reach the in-phase regime offered a bandwidth of approximately 1kHz.
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David Kabeya. Montée en brillance des réseaux de lasers à fibre : Nouvelle approche par diagnostic à contraste de phase dans une boucle d’optimisation. Optique / photonique. Université de Limoges, 2016. Français. ⟨NNT : 2016LIMO0116⟩. ⟨tel-01662407⟩

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