Mutual interactions of femtosecond pulses and transient gratings in nonlinear optical spectroscopy

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Titel: Mutual interactions of femtosecond pulses and transient gratings in nonlinear optical spectroscopy
Autor(en): Nolte, Stefan
ORCID des Autors: https://orcid.org/0000-0003-0100-9755
Erstgutachter: Prof. Dr. Mirco Imlau
Zweitgutachter: Prof. Dr. Dominik Schaniel
Zusammenfassung: This work is dedicated to a comprehensive experimental study on the interaction of femtosecond laser pulses with the nonlinear optical medium lithium niobate. The nonlinear optical response in the nanosecond regime was already studied extensively with a variety of techniques, whereas femtosecond pulses were mainly used in transient absorption or transient grating experiments. Naturally, the temporal resolution of these measurements depends on the pulse duration, however, dynamics during the pulse excitation were barely investigated. The motivation of this work is to widen the limits of femtosecond spectroscopy, not only to temporally resolve faster nonlinear optical processes, but further to show a sensitivity to other coupling mechanisms between the pulses and the material. Especially, the role of transient, dynamic holographic gratings is investigated with a careful determination of the pulse duration, bandwidth and frequency chirp. A basis of this work is established in the first part by studying the material response via light-induced absorption before focusing on the main topic, the pulse interaction with elementary (holographic) gratings, both self-induced and static, in the second part. By this detailed study, several features of femtosecond laser pulses, holographic gratings and the ultrafast material response can be revealed: (i) grating recording is feasible even with pulses of different frequencies, provided that their pulse duration is sufficiently short, (ii) grating based pulse coupling causes a pronounced energy transfer even in a common pump-probe setup for transient absorption measurements with (non-)degenerated frequencies, (iii) beyond expectation, oscillations in the phonon frequency range become apparent in different measurements. The presented results point towards appropriate future experiments to obtain a more consistent, microscopic model for the ultrafast response of the crystal, involving the interplay between photo-generated polarons, self-induced gratings, and phonons.
URL: https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-20181116828
Schlagworte: Nonlinear Optics; Ultrafast Physics; Holographic Gratings; Lithium Niobate; Spectroscopy; Two-Beam Coupling
Erscheinungsdatum: 16-Nov-2018
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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