Iteration of optical time reversal by ultrasonic encoding in biological tissue

An apparatus for focusing light within a scattering medium comprising:

• a coherent light source to emit a sample beam into the scattering medium;
• a movable ultrasound transducer to produce a focused ultrasound wave at one of at least two positions;
• a phase-conjugating device holographically recording an ultrasound-modulated wavefront as an interference pattern between an ultrasound-encoded portion of the sample beam and a reference beam, and holographically reading the ultrasound-modulated wavefront using a reconstruction beam to produce a phase-conjugated wavefront and delivering the phase-conjugated wavefront to the scattering medium;
• an optical assembly to direct the sample beam into the scattering medium at a first position and to direct the phase-conjugated wavefront to the scattering medium at a second position;
• and
• a controller to operate the coherent light source, the movable ultrasound transducer, the optical assembly, and the phase-conjugating device in a coordinated fashion.

A system for focusing light within a scattering medium comprising:

• a moveable ultrasound transducer operatively connected to the scattering medium to produce at least one focused ultrasound wave within each of a sequence of focus regions situated within the scattering medium;
• a coherent light source;
• an optical assembly operatively connected to the coherent light source, the scattering medium, and a phase-conjugating device, wherein the optical assembly receives one or more coherent light beams from the coherent light source, delivers a sample beam into the scattering medium, and delivers a reference beam and a reconstruction beam to the phase-conjugating device;
• the phase-conjugating device operatively connected to the scattering medium, wherein the phase-conjugating device:
• receives an ultrasound-encoded portion of the sample beam from the scattering medium;
• holographically records the ultrasound-modulated wavefront as an interference pattern between the ultrasound-encoded portion of the sample beam and the reference beam;
• holographically reads the ultrasound-modulated wavefront using the reconstruction beam to produce a phase-conjugated beam;
• and
• delivers the phase-conjugated beam to the scattering medium;
• and
• a controller operatively connected to the coherent light source, the optical assembly, the phase-conjugating device, and the ultrasound transducer, wherein the controller controls at least one of:
• the movement of the ultrasound transducer between each of the sequence of focal regions;
• the production of each of the at least one focused ultrasound waves by the ultrasound transducer;
• the delivery of the sample beam, the reference beam, and the reconstruction beam by the optical assembly;
• and
• the production of the one or more coherent light beams by the coherent light source.