Abstract
We use two-beam second-harmonic generation to address thin films of silicon nitride (SiN). This technique is able to distinguish between the dipolar and higher-multipolar (magnetic and quadrupolar) contributions to the nonlinearity, as earlier shown for bulk samples. Our results for the SiN films exhibit strong multipolar signatures. Nevertheless, the results can be fully explained by the strong dipolar response of SiN once multiple reflections of the fundamental and second-harmonic fields within the film are properly taken into account. The results show that the recognition of multipolar nonlinearities requires extreme care for samples typically used for the characterization of new materials.
Highlights
Multipole effects have been already utilized in nanostructured materials, the design guidelines for strong multipolar responses in bulk of materials are poorly understood, and such responses are difficult to address reliably in experiments
Multipole effects can be studied by second-harmonic generation with two non-collinear beams at the fundamental frequency [1,2]
This technique was originally developed for bulk samples and new materials are commonly characterized as thin films
Summary
Multipole effects have been already utilized in nanostructured materials, the design guidelines for strong multipolar responses in bulk of materials are poorly understood, and such responses are difficult to address reliably in experiments.
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