High-speed single-exposure time-reversed ultrasonically encoded optical focusing into scattering media with off-axis holography

Optical scattering limits the ability to focus light deep inside scattering media, posing a long-standing challenge in biomedical applications such as deep-tissue imaging and photodynamic therapy. Digital optical phase conjugation (DOPC), combined with ultrasonic guide stars-an approach named as time-reversed ultrasonically encoded (TRUE) optical focusing-has shown promise in overcoming this limitation. However, practical applications, such as imaging in living tissues, require TRUE systems to operate at high speeds to compensate for dynamic scattering caused by physiological motion. While single-exposure DOPC systems have achieved average mode time down to tens of nanoseconds, conventional TRUE systems require at least two camera exposures to separate ultrasonically encoded scattered light from the diffuse background, leading to increased system runtime. In this study, we developed a high-speed single-exposure TRUE focusing system based on off-axis holography. Our system achieves an overall system runtime of approximately 12.6 ms while supporting 4.2 × 10⁵ independently controllable modes. By dividing the system runtime by the number of independently controllable modes, the average mode time of the developed TRUE focusing system is calculated to be only 30 ns-more than seven times shorter than that of previously demonstrated single-exposure DOPC systems. This advancement significantly enhances the feasibility of optical focusing in dynamic scattering environments, paving the way for deep-tissue biomedical applications.