Focusing on moving targets through scattering samples.

Edward Haojiang Zhou,Benjamin Judkewitz,Haowen Ruan,Changhuei Yang

doi:10.1364/optica.1.000227

Abstract

Focusing light through scattering media has been a longstanding goal of biomedical optics. While wavefront shaping and optical time-reversal techniques can in principle be used to focus light across scattering media, achieving this within a scattering medium with a noninvasive and efficient reference beacon, or guide star, remains an important challenge. Here, we show optical time-reversal focusing using a new technique termed Time Reversal by Analysis of Changing wavefronts from Kinetic targets (TRACK). By taking the difference between time-varying scattering fields caused by a moving object and applying optical time reversal, light can be focused back to the location previously occupied by the object. We demonstrate this approach with discretely moved objects as well as with particles in an aqueous flow, and obtain a focal peak-to-background strength of 204 in our demonstration experiments. We further demonstrate that the generated focus can be used to noninvasively count particles in a flow-cytometry configuration-even when the particles are hidden behind a strong diffuser. By achieving optical time reversal and focusing noninvasively without any external guide stars, using just the intrinsic characteristics of the sample, this work paves the way to a range of scattering media imaging applications, including underwater and atmospheric focusing as well as noninvasive in vivo flow cytometry.

Highlights

Focusing light through highly scattering media is an important challenge in biomedical imaging, colloidal optics, and astronomy
When there is no direct access to the target plane, e.g., when the target plane is hidden within the sample, physical guide stars such as beads can be placed within the sample and used as reference beacons [9,10,11]
In this work we provided, to the best of our knowledge, the first demonstration of time-reversed optical focusing through scattering media by using the motion of a target object as a guide star—a technique we call TRACK

Summary

Introduction

Focusing light through highly scattering media is an important challenge in biomedical imaging, colloidal optics, and astronomy. When there is no direct access to the target plane, e.g., when the target plane is hidden within the sample, physical guide stars such as beads can be placed within the sample and used as reference beacons [9,10,11] Because this requires invasive insertion, recent research has focused on virtual, ultrasound-based guide stars relying on the acousto-optic [12,13,14,15,16] or the photo-acoustic effect [17,18,19,20]. Near-instantaneous time reversal at optical resolutions remains elusive

Methods

Results

Conclusion