Abstract
While propagating inside the strongly scattering biological tissue, photons lose their incident directions beyond one transport mean free path (TMFP, [Formula: see text]1 millimeter (mm)), which makes it challenging to achieve optical focusing or clear imaging deep inside tissue. By manipulating many degrees of the incident optical wavefront, the latest optical wavefront engineering (WFE) technology compensates the wavefront distortions caused by the scattering media and thus is toward breaking this physical limit, bringing bright perspective to many applications deep inside tissue, e.g., high resolution functional/molecular imaging, optical excitation (optogenetics) and optical tweezers. However, inside the dynamic turbid media such as the biological tissue, the wavefront distortion is a fast and continuously changing process whose decorrelation rate is on timescales from milliseconds (ms) to microseconds ([Formula: see text]s), or even faster. This requires that the WFE technology should be capable of beating this rapid process. In this review, we discuss the major challenges faced by the WFE technology due to the fast decorrelation of dynamic turbid media such as living tissue when achieving light focusing/imaging and summarize the research progress achieved to date to overcome these challenges.
Highlights
Light is a widespread and noninvasive tool with high spatial resolution which is useful for applications in theelds of in vivo medicine, biomedical imaging and treatments including various microscopy imaging, photodynamic operations, physiotherapy, etc
Signicant progress has been made on the development of optical wavefront engineering (WFE), which opened the door for high-resolution imaging and energy delivery deep inside strongly scattering media, and made breakthroughs on application-oriented explorations inelds of optogenetics,[36,53,78,83,84,85] high-resolution microscopy imaging,[86,87,88] endoscopic imaging,[79,89,90,91,92,93] etc
According to di®erent technical implementation routes, optical WFE approaches are divided into four main categories including analog optical phase conjugation (AOPC), digital optical phase conjugation (DOPC), iterative wavefront optimization and transmission matrix (TM) measurement
Summary
Light is a widespread and noninvasive tool with high spatial resolution which is useful for applications in theelds of in vivo medicine, biomedical imaging and treatments including various microscopy imaging, photodynamic operations, physiotherapy, etc. When biological scattering media have destroyed the wavefront of light propagation, optical WFE is able to detect and correct these distortions and might achieve high-quality optical imaging/focusing through or inside the scattering media. For in vivo functional/molecular imaging, high energy optical focusing is able to enhance the strength and contrast of detected signals and break through the physical limits of existing methods on sensitivity, resolution and depth of investigation. 3–5 mainly introduce the principles and latest progress of analog optical phase conjugation (AOPC), digital optical phase conjugation (DOPC), feedback-based iterative wavefront optimization and TM approaches, respectively, Sec. 6 is the discussion and conclusion for the development, challenges and perspective of fast WFE
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