High-speed single-exposure time-reversed ultrasonically encoded optical focusing against dynamic scattering

Abstract

Focusing light deep inside live scattering tissue promises to revolutionize biophotonics by enabling deep tissue noninvasive optical imaging, manipulation, and therapy. By combining with guide stars, wavefront shaping is emerging as a powerful tool to make scattering media optically transparent. However, for in vivo biomedical applications, the speeds of existing techniques are still too slow to accommodate the fast speckle decorrelation of live tissue. To address this key bottleneck, we develop a quaternary phase encoding scheme to enable single-exposure time-reversed ultrasonically encode optical focusing with full-phase modulations. Specifically, we focus light inside dynamic scattering media with an average mode time down to 29 ns, which indicates that more than 10 4 effective spatial modes can be controlled within 1 millisecond. With this technique, we demonstrate in vivo light focusing in between a highly opaque adult zebrafish of 5.1 millimeters in thickness and a ground glass diffuser. Our work presents an important step toward in vivo deep tissue applications of wavefront shaping.

Performance enhancement in wavefront shaping of multiply scattered light: a review

“…For example, in an identical DOPC system, 40 ∼10 6 DoFs leads to a latency ∼5.4 ms and ∼10 5 DoFs to ∼1 ms, which is nonlinearly related. Nevertheless, the overall direction to improve the efficiency of OPC-based WFS focuses on accelerating the DOPC scheme, such as introducing QEPM to enable single-shot full phase modulation TRUE focusing within 1 ms, 77 or enhancing the energy of phase conjugated light in AOPC by introducing a gain module in the system to accumulate the energy gain to approach or exceed the unity. 87 Last but not the least, it must be admitted that till to date WFS still sees technical challenges for applications in thick and dynamic complex media, such as living biological tissues, due to insufficient understanding and solution of the multiply scattering process.…”

“…Different from precompensation WFS, OPC does not need numerous iterations for optical focusing but usually a few or one exposure is sufficient to form a sharp and tight focus. 27 , 77 Such a rapid response is essentially compatible with bio-applications whose correlation window is on the scale of milliseconds in vivo . The rapid response also allows for more DoFs being adopted for modulation without consuming too much time, and hence higher modulation efficiency could be expected.…”

“…To address that, a more recent study introduces a quaternary phase encoded mask (QPEM) to accomplish the four-step phase shifting in one shot [ Fig. 6(d) ], 77 with a graphic processing unit (GPU) for data processing [ Fig. 6(a) ].…”

“…Dynamic focusing with a FPGA-DMD configuration in a DOPC system: 40 (a) the schematic experimental setup; (b) decorrelation of the back on a living mouse; and (c) dynamic focusing during the decorrelation. High-speed single-shot TRUE focusing with full phase modulation: 77 (d) DOPC setup with a QPEM and a GPU; (e) configuration for TRUE focusing in between the zebrafish and a ground glass diffuser; and (f) dynamic focusing realized in (e). Images (a)–(c) and (e), (f) are reproduced with permission from Refs.…”

“…Different from precompensation WFS, OPC does not need numerous iterations for optical focusing but usually a few or one exposure is sufficient to form a sharp and tight focus 27 , 77 . Such a rapid response is essentially compatible with bio-applications whose correlation window is on the scale of milliseconds in vivo .…”