New insight into the interaction of light with tailored and photofunctional materials: the role of (dis-)order, periodicity and symmetry

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Title: New insight into the interaction of light with tailored and photofunctional materials: the role of (dis-)order, periodicity and symmetry
Authors: Bourdon, Björn
ORCID of the author: https://orcid.org/0000-0002-4559-4522
Thesis advisor: Prof. Dr. Mirco Imlau
Thesis referee: Prof. Dr. Joachim Wollschläger
Abstract: Within this thesis, photo-induced mechanisms of the light-matter interaction are investigated in tailored and photofunctional materials that differ significantly in their optical and structural properties. The individual coupling mechanisms in congruently melted, nominally undoped or iron doped lithium niobate crystals as well as in structurally disordered photoswitchable molecules embedded into a solid state polymer are examined in particular by the principle of holographic grating recording and transient absorption spectroscopy which provide new insight into a variety of material response properties. In case of photoswitchable ruthenium sulfoxide compounds, the underlying mechanism can be unambiguously assigned to a photochromic material response evoked by a photochemical reaction, i.e., a non-instantaneous, local ligand isomerisation. Comparable results are obtained for iron-doped, oxidized lithium niobate where holographic grating recording is related to the photophysical generation of transient excitonic states whose photochromic properties are characterized by targeted ns-pump, supercontinuum probe spectroscopy. In the event of nominally undoped lithium niobate, the holographic amplification of two sub-picosecond pulses is attached to the phenomenon of two-beam coupling on a self-induced dynamic grating. By correlating the individually obtained mechanisms of the light-matter interaction and the light-induced material response, generally accepted conclusions on a microscopic level can be achieved. A major influence of the internal structure and orientation of the excited states, i.e., an appropriate threedimensional structural arrangement, is deduced as a prerequisite for the formation of light-induced, macroscopic refractive index changes while absorption and microscopic refractive index alterations linked via the Kramers-Kronig relation are unaffected. In systems featuring a random distribution of excited states, an orientational order might be achieved as a consequence of linear polarized light, i.e., by polarization structuring. Moreover, if the photorefractive effect can be ruled out, the material response in lithium niobate can be solely assigned to a local alteration of the transient electronic states, i.e., to the photochromic properties of polarons and/or excitonic states, which is in particular comparable to the linkage isomerism of molecular photoswitchable molecules. In addition, the influence of structural parameters on the light-matter/surface interaction is studied on the μm-scale by analyzing the diffraction phenomenon arising from a relief grating. A considerable impact on the surface grating assisted coupling is determined by the transition from cw-lasers to ultrashort laser pulses which enables interference quenching. However, this phenomenon is of no consequence in case of selfinduced holographic gratings.
URL: https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-202002262629
Subject Keywords: light-matter interaction; photoswitchable molecules; tailored materials; lithium niobate; holographic gratings; self-trapped excitons
Issue Date: 26-Feb-2020
License name: Attribution 3.0 Germany
License url: http://creativecommons.org/licenses/by/3.0/de/
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB04 - E-Dissertationen

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