High-speed photoacoustic-guided wavefront shaping for focusing light in scattering media

Abstract

Wavefront shaping is becoming increasingly attractive as it promises to enable various biomedical applications by breaking through the optical diffusion limit that prevents light focusing at depths larger than ∼1mm in biological tissue. However, despite recent advancements in wavefront shaping technology, such as those exploiting non-invasive photoacoustic-guidance, in vivo demonstrations remain challenging mainly due to rapid tissue speckle decorrelation. In this work, we report a high-speed photoacoustic-guided wavefront shaping method with a relatively simple experimental setup, based on the characterization of a scattering medium with a real-valued intensity transmission matrix. We demonstrated light focusing through an optical diffuser by optimizing 4096 binary amplitude modulation modes of a digital micromirror device within ∼300ms, leading to a system runtime of 75 µs per input mode, which is 3 orders of magnitude smaller than the smallest runtime reported in literature so far using photoacoustic-guided wavefront shaping. Thus, our method is a solid step forward toward in vivo applications of wavefront shaping.

Fig. 1.

Schematic illustration of the experimental setup and principle. AWG, arbitrary waveform generator; Amp, amplifier; L1–L3, convex lenses.

Fig. 2.

Focusing light through an optical diffuser. (a) Comparison of photoacoustic (PA) signals generated with random DMD patterns and an optimal DMD pattern. The blue line is an average of 64 PA signals acquired when 64 random DMD patterns were displayed, and the red line is an average of 64 PA signals when an optimal DMD pattern was displayed. (b) Lateral and (c) vertical intensity profiles along the dashed lines in the captured optical speckle patterns at the absorber plane when (d) a random DMD pattern and (e) an optical pattern were displayed. (f) The same optical speckle pattern as in (e) when a neutral density filter was used to attenuate the light intensity to avoid overexposure. To facilitate comparison, the light intensity values in (f) have taken into account the light attenuation by the filter. a.u., arbitrary unit.

Fig. 3.

Workflow of the RVITM-based wavefront shaping for focusing light through scattering media. The total system runtime is 306 ms, and the total number of input DMD modes is 4096. DAQ, data acquisition.