Effect of refractive index mismatch on forward-to-backward ratios in SHG imaging

Jarno N. van der Kolk, Stéphane Bancelin, Charalambos Kioulos, Antonino Calà Lesina, François Légaré, Lora Ramunno
Opt. Lett.. 2018-10-11; 43(20): 5082
DOI: 10.1364/OL.43.005082


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Nonlinear optical imaging in the epi-direction is used to image subresolution
features. We find that a refractive index mismatch between the object to be
imaged and the background medium can change the far-field intensity image. As an
example, we study second harmonic generation (SHG) microscopy where the
forward-to-backward (F/B) ratio is used to quantify subresolution features. We
show both theoretically and experimentally that the inhomogeneous refractive
index in collagen tendon tissue creates near-field effects, which can change the
F/B ratio by ∼20%-25%, even though the effect is negligible for most of the
individual fibrils in the tissue. This is caused by the sensitivity of the
backward signal on phase matching conditions.

Auteurs Bordeaux Neurocampus