Abstract
Light scattering in biological tissue significantly limits the accessible depth for localized optical interrogation and deep-tissue optical imaging. This challenge can be overcome by exploiting the time-reversal property of optical phase conjugation (OPC) to reverse multiple scattering events or suppress turbidity. However, in living tissue, scatterers are highly movable and the movement can disrupt time-reversal symmetry when there is a latency in the OPC playback. In this paper, we show that the motion-induced degradation of the OPC turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation - a popular conventional measure of scatterer movement. We investigated this decorrelation characteristic time through a 1.5-mm-thick dorsal skin flap of a living mouse and found that it ranges from 50 ms to 2.5 s depending on the level of immobilization. This study provides information on relevant time scales for applying OPC to living tissues.
Highlights
Optical phase conjugation (OPC) is the process whereby an incoming light field is reproduced and played back in the backward direction such that the phase-conjugated light beam corresponds to a time-reversed input beam [1]
We show that the motioninduced degradation of the optical phase conjugation (OPC) turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation – a popular conventional measure of scatterer movement
A photorefractive medium was used for the holographic recording and readout [2,3,10]. In biomedical applications such as fluorescence imaging and photodynamic therapy, its application is limited by its low OPC amplification, which is defined by the power ratio between the phaseconjugated beam and the input signal beam
Summary
Optical phase conjugation (OPC) is the process whereby an incoming light field is reproduced and played back in the backward direction such that the phase-conjugated light beam corresponds to a time-reversed input beam [1] For biomedical applications, this time-reversal property can be used to increase the accessible depth of light inside biological tissue by cancelling out multiple scattering (Fig. 1, right top) [2,3]. The latency of the OPC technique was as high as ~5 s, since the OPC playback in that experiment was generated using a photorefractive crystal, which is slow to record and read out The latter deficiency was significant because it prevented any observation of turbidity suppression effects that have fast decorrelation time constants. We found that turbidity suppression can be achieved even at an extremely low-intensity autocorrelation (
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
