Breaking Acoustic Limit of Optical Focusing Using Photoacoustic‐Guided Wavefront Shaping

Abstract

Optical wavefront shaping (WFS) has been demonstrated as a powerful tool for focusing light in opaque scattering media. Photoacoustic (PA)‐guided WFS, in particular, has raised a lot of interest because of its non‐invasive approach of light focusing by utilizing endogenous optical absorption information inside complex samples. In general, the optical focus after PA‐guided WFS is limited by the focus of the ultrasound transducer. To date, a number of approaches have been developed to tackle this problem, allowing a sub‐acoustic focal spot to be achieved deep within scattering samples. This review introduces these developments in PA‐guided WFS, highlighting their fundamental principles as well as their merits and limitations. Furthermore, the rules that govern the optical focusing ability of PA‐guided WFS are provided, and the outlook and remaining challenges for future advances are discussed. These insights will facilitate further breakthroughs in PA‐guided WFS.

Robust and adjustable dynamic scattering compensation for high-precision deep tissue optogenetics

“…The focusing performance is also decreasing with the increasing scattering and absorption of the brain slices, while the focus is still clearly recognizable (Fig. 3h) with the maximum average PBR of the value about 35. The details about the system adjustments for the larger focus are discussed in Supplementary Method 3.…”

“…Wavefront shaping strategies counteract the effects of tissue scattering using different properties of the light field (phase, intensity, or propagation direction) to tailor the incident wavefront and modulate the light field, so the incident light can be directed to the target location fast and optimally. Several typical wavefront shaping mechanisms have been reported, including parallel iteration 15,[19][20][21][22][23][24][25][26] , transmission matrix 22,[27][28][29][30] , and optical phase conjugation 13,18,[31][32][33][34] or other mainly ultrasound-based methods 17,35,36 . Among these methods, the spatial resolution of ultrasound-based mechanisms is still limited by the ultrasonic guidestar diffraction limit, which is much greater than the optical diffraction limit.…”

Influence mechanism of the temporal duration of laser irradiation on photoacoustic technique: a review

“…Based on the nonlinearity PA rules, as outlined in previous studies 2 , 29 that examined how the nonlinear mathematical structure governs its utilization, it can be inferred that this pulse-duration-dependent nonlinearity holds potential for interesting applications such as super resolution achievement 2 and PA-assisted wavefront shaping. 29 …”

“… 7 , 15 – 26 PA imaging is based on the PA effect, wherein biological tissues are illuminated by a nonionizing short-pulsed laser beam or rapidly modulated radiation as probing energy. 1 , 3 , 4 , 27 – 32 The illumination induces temporally confined optical absorption, which converts into heat, causing a transient local temperature increase. This increase in temperature leads to thermal-elastic expansion, resulting in an initial pressure rise that propagates as wideband frequency ultrasonic waves.…”

Wavefront shaping improves the transparency of the scattering media: a review

“…In addition, people have proposed several noninvasive guide stars, such as coherence gating 76 and particle displacement 77 . Recently, acousto-optic feedback methods have been extensively studied, 66 , 69 , 78 – 80 as ultrasound can propagate deep in biological tissue. In addition, the acoustic signal generated via the photoacoustic effect inside the scattering medium as the feedback was also explored 29 , 81 .…”