• Acta Photonica Sinica
  • Vol. 50, Issue 12, 1229002 (2021)
TIAN Bingxin, HAN Jun*, LIU Bingcai, and GONG Changmei
Author Affiliations
  • School of Optoelectronic Engineering, Xi'an Technological University, Xi'an 710021, China
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    DOI: 10.3788/gzxb20215012.1229002 Cite this Article
    Bingxin TIAN, Jun HAN, Bingcai LIU, Changmei GONG. A Method on Non-invasive Focusing in Scattering Medium[J]. Acta Photonica Sinica, 2021, 50(12): 1229002 Copy Citation Text show less

    Abstract

    The existing non-invasive focusing technology has the problems of complex calculation, low anti-noise performance and slow optimization speed. Therefore, a wavefront shaping-based method is proposed. Based on the linear excitation of fluorescence, by maxmizing the linear combination of the intensity and contrast of the detected fluorescent speckle in an appropriate contribution, a phase-only spatial light modulator is used to optimize the input light so as to realize the focusing in the scattering medium. The experimental results show that the proposed method not only realizes deep focusing on a single particle in the scattering medium, but also has a fast convergence speed and is insensitive to noise. Moreover, it provides a new way for non-invasive deep imaging in complex medium and is expected to be used in life science.

    0 Introduction

    Propagation of light in materials with inhomogeneous refractive index, such as biological tissues, is affected by multiple scattering, resulting in complicated interference patterns, known as speckle1, which limits the application of conventional optical method and makes it hard to focus and image in such medium. Recent years, many efforts have been devoted to developing methods such as wavefront shaping and ghost imaging so as to enable focusing and imaging objects behind or inside scattering media2-6. In 2007, VELLEKOOP I M7 optimized the input laser speckle by maximizing the input laser intensity in the scattering medium, to focus on a specified position in the scattering medium. However, most of them are invasive since they require either the presence of a detector8-9 or a “guide star”10 to be placed behind or within the scattering medium. In 2012, BERTOLLOTII J et al.11 proposed an optical method which first verified the possibility of non-invasive imaging through the scattering medium. It realized the imaging of a fluorescent object hidden behind a thin scattering layer by collected the total fluorescence using a bucket detector, without access to the region behind the scattering medium. This method was later extended to noninvasive imaging of scattering media using spatially incoherent light and ordinary cameras12. While, since it relied on the speckle correlation, this technique is limited by optical memory effect. Based on the concept of non-invasive detection, KATZ O et al.13 proposed a nonlinear wavefront shaping method to achieve focusing by maximizing two-photon fluorescence intensity. In this method, the nonlinear signal from the fluorescence object is obtained, and the maximum fluorescence is achieved when the excitation light is converged as closely as possible. However, the nonlinear signal needs to use ultrafast laser source, which is not suitable for continuous wave laser imaging. Since then, different wavefront shaping technologies based on linear focusing14-15 used in linear fluorescence microscope technology, speckle correlation16-17, and transmission matrix18 have emerged in succession. However, these methods tried to converge the excitation light as closely as possible by monitoring the total fluorescence intensity resulting in a bad focus. In recent years, a linear focusing method using speckle variance optimization was proposed19-20 which can solve the problem to some extend.

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    Bingxin TIAN, Jun HAN, Bingcai LIU, Changmei GONG. A Method on Non-invasive Focusing in Scattering Medium[J]. Acta Photonica Sinica, 2021, 50(12): 1229002
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