Noninvasive nonlinear focusing and imaging through strongly scattering turbid layers

Ori Katz,Yefeng Guan,Yaron Silberberg,Eran Small

doi:10.1364/optica.1.000170

Abstract

Diffraction-limited imaging through complex scattering media is a long sought after goal with important applications in biomedical research. In recent years, high resolution wavefront-shaping has emerged as a powerful approach to generate a sharp focus through highly scattering, visually opaque samples. However, it requires a localized feedback signal from the target point of interest, which necessitates an invasive procedure in all-optical techniques. Here, we show that by exploiting optical nonlinearities, a diffraction-limited focus can be formed inside or through a complex sample, even when the feedback signal is not localized. We prove our approach theoretically and numerically, and experimentally demonstrate it with a two-photon fluorescence signal through highly scattering biological samples. We use the formed focus to perform two-photon microscopy through highly scattering, visually opaque layers.

Highlights

The inherent inhomogeneity of complex samples such as biological tissues induces light scattering, which limits the resolution of light focusing and poses a major hurdle to deep-tissue microscopy[1]
We demonstrate that this focus can be used for nonlinear imaging in reflection-mode in a totally noninvasive manner
The image that was obtained with the optimized focus (Fig. 2b) is not just of higher resolution and contrast, when compared to the blurred standard two-photon microscopy image, but is approximately an order of magnitude brighter than an image obtained without optimization (Fig 2a)

Summary

Introduction

The inherent inhomogeneity of complex samples such as biological tissues induces light scattering, which limits the resolution of light focusing and poses a major hurdle to deep-tissue microscopy[1]. We show that by exploiting optical nonlinearities, a diffraction-limited focus can be formed inside or through a complex sample, even when the feedback signal is not localized.

Results

Conclusion