Figure 3

Illustration of the two-stage TRMCP focusing procedure. (a,b) Hologram recording stage: sample and reference beams interfere, with a camera to record the interference patterns when the magnetically controlled microsphere is at Location 1 and 2, respectively. The Light field difference ΔE is computed and stored. (c) Hologram playback stage: the playback beam (identical to the reference beam) is modulated by the SLM with a phase pattern ΔE^* (the conjugate of ΔE), generating a phase conjugation copy of ΔU. The new light travels back to the scattering medium, albeit tortuously, and converges to the point of origin—the magnetically controlled moving microsphere.