While a three-dimensional (3D) scattering medium is from the outset opaque, such a medium sustains intriguing transport channels with near-unity transmission that are pursued for fundamental reasons and for applications in solid-state lighting, random lasers, solar cells, and biomedical optics. Here, we study the 3D spatially resolved distribution of the energy density of light in a 3D scattering medium upon the excitation of highly transmitting channels. The coupling into these channels is excited by spatially shaping the incident optical wavefronts to a focus on the back surface. To probe the local energy density, we excite isolated fluorescent nanospheres distributed inside the medium. From the spatial fluorescent intensity pattern we obtain the position of each nanosphere, while the total fluorescent intensity gauges the energy density. Our 3D spatially resolved measurements reveal that the differential fluorescent enhancement changes with depth, up to $26\times$ at the back surface of the medium, and the enhancement reveals a strong peak versus transverse position. We successfully interpret our results with a newly developed 3D model without adjustable parameters that considers the time-reversed diffusion starting from a point source at the back surface.

中文翻译：

---

波前整形增强三维空间分辨光能密度

三维（3D）散射介质从一开始就是不透明的，但这种介质会通过近乎统一的传输来维持引人入胜的传输通道，这是出于根本原因以及在固态照明，随机激光器，太阳能电池和固态照明中的应用所追求的。生物医学光学。在这里，我们研究了高透射通道激发后3D散射介质中光的能量密度的3D空间分辨分布。通过对入射光波前进行空间整形以聚焦在背面上，可以激发耦合到这些通道中。为了探测局部能量密度，我们激发了分布在介质内部的孤立的荧光纳米球。从空间荧光强度模式，我们可以获得每个纳米球的位置，而总荧光强度则用于衡量能量密度。$26\times$在介质的背面，并且增强显示出相对于横向位置的强峰。我们使用不带可调参数的新开发的3D模型成功地解释了我们的结果，该模型考虑了从背面的点源开始的时间反向扩散。