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Promotionsvortrag Physik: "Angular momentum control via Raman conversion in twisted gas-filled photonic crystal fibre"

Jan 21
21. Januar 2021 15:00 Uhr bis 16:00 Uhr
Bibliothek A. 2.500, MPL, Staudtstr. 2, Erlangen

Ankündigung des Promotionsvortrags von: Sona Löwe (geb. Davtyan)

Light coupled in twisted single-ring hollow-core photonic crystal fibre (HC-PCF) is force to rotate as it propagates, introducing circular birefringence, which lifts the degeneracy between the refractive indices of circularly-polarized guided modes with opposite handedness. This new type of chiral fibres can be fabricated either by introducing a continuous longitudinal twist to the structure during drawing or via post-processing of an existing untwisted fibre. Optical activity makes twisted HC-PCFs an ideal platform to study strong polarization-dependent nonlinear interactions such as stimulated Raman scattering (SRS). In SRS, pump photons interact with Raman-active molecules giving rise to the generation of a red-shifted Stokes signal along with coherence waves of synchronized molecular motion, which can be used for further amplification of the Stokes signal or the generation of up-shifted anti-Stokes bands.

This thesis reports on a study of chiral nonlinear interactions in twisted HC-PCFs filled with hydrogen. The unique platform allows full control over the polarization state of laser lines generated and amplified via stimulated Raman scattering in the gaseous fibre core, something not possible in the untwisted version of PCF. Moreover, the onset of intra-polarization gain suppression allows adjustment of the polarization state of the frequency-shifted Raman bands by simple tuning of the gas pressure.

The results demonstrate a novel approach for the robust excitation, collinear wavelength conversion and guidance of light carrying both spin and orbital angular momentum based on twisted single-ring HC-PCF. The results show successful excitation of guided vortex modes in the central hollow channel of HC-PCF with launching efficiencies reaching 75%. Such high efficiency, combined with a low attenuation, tight modal confinement and wide transmission window, allows nonlinear frequency conversion of the generated vortices via SRS in a hydrogen-filled hollow-core fibre. In this system, the generated vortex coherence waves carry angular momentum in addition to the linear momentum, which enables the transfer of angular momentum between the different Raman sidebands.

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(Vortrag auf Englisch)

Dem Vortrag schließt sich eine Diskussion von 15 Minuten an. Vortrag und Diskussion sind aufgrund der momentanen Situation nicht öffentlich. Diesen Verfahrensteilen folgt ein ebenfalls nicht öffentliches Rigorosum von 45 Minuten.