Fritzsche Niklas, Ott Felix, Pink Karsten, Kienle Alwin
Institut für Lasertechnologien in der Medizin und Meßtechnik an der Universität Ulm, D-89081 Ulm, Germany.
Faculty of Natural Sciences, Ulm University, D-89081 Ulm, Germany.
Sensors (Basel). 2023 Oct 11;23(20):8397. doi: 10.3390/s23208397.
Manipulating the wavefront of coherent light incident on scattering media to enhance the imaging depth, sensitivity, and resolution is a common technique in biomedical applications. Local phase variations cause changes in the interference and can be used to create a focus inside or behind a scattering medium. We use wavefront shaping (WFS) to force constructive interference at an arbitrary location. The amount of light transmitted into a given region strongly depends on the scattering and absorption characteristics. These are described by their respective coefficients μs and μa and the scattering phase function. Controlling the scattering and absorption coefficients, we study the behavior of wavefront shaping and the achievable intensity enhancement behind volume scattering media with well-defined optical properties. The phantoms designed in this publication are made of epoxy resin. Into these epoxy matrices, specific amounts of scattering and absorbing particles, such as titanium dioxide pigments and molecular dyes, are mixed. The mixture obtained is filled into 3D-printed frames of various thicknesses. After a precise fabrication procedure, an integrating sphere-based setup characterizes the phantoms experimentally. It detects the total hemispherical transmission and reflection. Further theoretical characterization is performed with a newly developed hybrid PN method. This method senses the flux of light into a particular angular range at the lower boundary of a slab. The calculations are performed without suffering from ringing and fulfill the exact boundary conditions there. A decoupled two-path detection system allows for fast optimization as well as sensitive detection. The measurements yield results that agree well with the theoretically expected behavior.
在生物医学应用中，操纵入射到散射介质上的相干光的波前来提高成像深度、灵敏度和分辨率是一种常用技术。局部相位变化会引起干涉变化，可用于在散射介质内部或后方形成焦点。我们使用波前整形（WFS）来强制在任意位置产生相长干涉。传输到给定区域的光量很大程度上取决于散射和吸收特性。这些特性由它们各自的系数μs和μa以及散射相位函数来描述。通过控制散射和吸收系数，我们研究了波前整形的行为以及在具有明确光学特性的体散射介质后方可实现的强度增强。本出版物中设计的体模由环氧树脂制成。在这些环氧树脂基体中，混合特定量的散射和吸收颗粒，如二氧化钛颜料和分子染料。将得到的混合物填充到各种厚度的3D打印框架中。经过精确的制造过程后，基于积分球的装置对体模进行实验表征。它检测总的半球透射和反射。使用新开发的混合PN方法进行进一步的理论表征。该方法可感测平板下边界处进入特定角度范围的光通量。计算过程中不会出现振铃现象，并且在那里满足精确的边界条件。解耦双路径检测系统允许快速优化以及灵敏检测。测量结果与理论预期行为吻合良好。
