Nonlinear focal mapping of ferroelectric domain walls in LiNbO3: Analysis of the SHG microscopy contrast mechanism

Autor: Alex Widhalm, Gerhard Berth, Artur Zrenner, Michael Rüsing, P. Mackwitz, K. J. Spychala, Christine Silberhorn
Rok vydání: 2020
Předmět:
Zdroj: Journal of Applied Physics. 128:234102
ISSN: 1089-7550
0021-8979
Popis: Second-harmonic (SH) microscopy is a widely used tool for the study of ferroelectric domains, domain walls, and their substructure. Yet, the contrast mechanism, particularly for the commonly used large numerical aperture, is not fully understood. In this work, we examine the contrast mechanism of SH microscopy in periodically poled LiNbO3 for the case of tightly focused laser beams and in the surface-near regime. The results are interpreted along theoretical calculations that include a vectorial field model for excitation and detection. Our model suggests that the characteristic contrasts mainly originate from interference patterns in the signal due to the sign change of the nonlinear susceptibility at the domain boundary. We find that for large numerical apertures, the tight focusing induces polarization components (axial and orthogonal to incident polarization), and the subsequent mixing of differently polarized light fields via off diagonal tensor elements plays an important role for the domain wall contrast. With our model-based analysis, this work represents the foundation for the investigation of the substructure of domain walls with second-harmonic microscopy.
Databáze: OpenAIRE