Regensburg 2019 – wissenschaftliches Programm

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 10: Ferroics - Domains and Domain Walls

KFM 10.11: Vortrag

Dienstag, 2. April 2019, 12:35–12:50, H47

Nonlinear optical crystals in tightly focused laser beams: A spatially resolved second-harmonic analysis in the focal plane — •Kai Spychala, Peter Mackwitz, Alex Widhalm, Gerhard Berth, and Artur Zrenner — Department Physik, Universität Paderborn, 33098 Paderborn, Germany

In this work the nonlinear light-matter interaction in tightly focused optical systems is characterized. The study comprises the development of a theoretical model and a detailed experimental verification of the behaviour of second-harmonic (SH) generation in nonlinear optical crystals by focused light beams. We apply a direct imaging technique which records the spatial distribution of the second-harmonic signal in the back focal plane. Besides a profound understanding of the interaction which takes place in the focal region, the objective of this work is to develop the necessary numerical tool kit for in-depth data analysis. Our rigorous simulation, which is based on a vectorial description of the propagating light-fields, models the generated nonlinear signal in the case of (high NA) SH-microscopy and is verified via focal plane mapping in lithium niobate and potassium titanyl phosphate in a surface near regime. The calculations predict the symmetry and shape of the corresponding signals very well. In combination with experimental results it is now possible to extract information about the crystal symmetry. In this respect, our experiments verify the vectorial interaction processes, which lead to a specific and well-understood response in the SH signal.