Iteration of optical time reversal by ultrasonic encoding in biological tissue

Patent metadata

Field	Value
Publication number	US-9335605-B2
Application number	US-201314026577-A
Country	US
Kind code	B2
Filing date	Sep 13, 2013
Priority date	Jan 25, 2010
Publication date	May 10, 2016
Grant date	May 10, 2016

Abstract

Iterating an optical phase conjugation of ultrasonically-modulated diffuse light emitted by a scattering medium includes illuminating the scattering medium with a light beam from a coherent light source, modulating the diffuse light transmitted through the scattering medium with an ultrasonic wave focused on a region of interest within the scattering medium, fixing a hologram, retro-reflectively illuminating the scattering medium using a phase-conjugated copy of the diffuse light that was ultrasonically modulated, moving the ultrasonic focus, and iterating until light is focused on the final target.

First claim

What is claimed is:

1. A method for focusing light within a scattering medium comprising:
illuminating the scattering medium with a sample beam from a coherent light source, wherein the scattering medium comprises an ultrasound focus containing a focused ultrasound wave at a first position;
obtaining a first signal beam emerging from the scattering medium comprising a first ultrasound-modulated wavefront, wherein the first ultrasound-modulated wavefront comprises a portion of the sample beam which has passed through the ultrasound focus at the first position;
recording the first ultrasound-modulated wavefront from the first signal beam;
advancing the ultrasound focus to a second position within the scattering medium;
illuminating the scattering medium with a first phase-conjugated wavefront corresponding to the first ultrasound-modulated wavefront;
obtaining a second signal beam emerging from the scattering medium comprising a second ultrasound-modulated wavefront, wherein the second ultrasound-modulated wavefront comprises a portion of the first phase-conjugated wavefront which has passed through the ultrasound focus at the second position; and
recording the second ultrasound-modulated wavefront from the second signal beam.

2. The method of claim 1 , further comprising iteratively illuminating a plurality of additional positions in the scattering medium by:
advancing the ultrasound focus to each of a plurality of additional positions within the scattering medium;
illuminating the scattering medium with each of a plurality of additional phase-conjugated wavefronts, wherein:
the first additional phase-conjugated wavefront corresponds to the second ultrasound-modulated wavefront; and
each subsequent phase-conjugated wavefront of the plurality of phase-conjugated wavefronts corresponds to an additional ultrasound-modulated wavefront obtained with the ultrasound focus situated at a previous position;

obtaining each of a plurality of additional signal beams emerging from the scattering medium, wherein each additional signal beam comprises a portion of an additional phase-conjugated wavefront which has passed through the ultrasound focus at each additional position; and
recording each of the plurality of additional ultrasound-modulated wavefronts corresponding to one of the plurality of additional phase-conjugated wavefronts.

3. The method of claim 1 , wherein the total energy of each phase-conjugated wavefront is greater than or equal to the total energy of its corresponding ultrasound-modulated wavefront.

4. The method of claim 1 , wherein each ultrasound-modulated wavefront is recorded on a phase-conjugating device.

5. The method of claim 1 , wherein the focused ultrasound wave is produced using at least one ultrasound transducer.

6. The method of claim 5 , wherein the focused ultrasound wave is produced using an array of at least two ultrasound transducers.

7. The method of claim 1 , wherein each phase-conjugated wavefront is produced by reading a holographically recorded interference pattern using a phase-conjugate of the reference beam, or by illuminating a spatial light modulator displaying a wavefront of the ultrasound-modulated light with the phase-conjugate of the reference beam.

8. The method of claim 1 , wherein any two adjacent positions of the ultrasound focus are separated by a step size of no more than about one transport mean free path.

9. The method of claim 1 , wherein a time to move between any two adjacent positions is no more than a speckle decorrelation time.

10. 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.

11. The apparatus of claim 10 , wherein an energy of the phase-conjugated wavefront is greater than or equal to a total energy of the corresponding ultrasound-modulated wavefront.

12. The apparatus of claim 10 , further comprising a detector.

13. The apparatus of claim 10 , further comprising at least one acousto-optic modulator to frequency shift the sample beam by an amount equal to a central frequency of the ultrasound wave.

14. The apparatus of claim 10 , wherein the phase-conjugating device is a photorefractive material or a digital holography device and a spatial light modulator.

15. The apparatus of claim 10 , wherein the phase-conjugating device records an interference pattern between the signal beam emitted by the scattering medium and a reference beam and stores the interference pattern as a hologram.

16. The apparatus of claim 15 , wherein the phase-conjugating device reads the hologram using a reconstruction beam that is a phase-conjugate of the reference beam.

17. 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.

18. The system of claim 17 , further comprising an acousto-optic modulation device operatively connected to the optical assembly, wherein the acousto-optic modulation device modifies the frequency of either A) the

Assignees

• Univ Washington
• Univ Washington

Inventors

• Wang Lihong
• Xu Xiao

Classifications

• G03H1/0465

  Particular recording light; Beam shape or geometry (G03H1/06 takes precedence) · CPC title

• G03H2001/0083

  for restoring distorted objects, e.g. restoring objects through scattering media · CPC title

• G03H1/04

  Processes or apparatus for producing holograms (G03H1/26 takes precedence) · CPC title

• G03H1/22

  Processes or apparatus for obtaining an optical image from holograms (G03H1/26 - G03H1/34 take precedence) · CPC title

• G03H1/0005 Primary

  Adaptation of holography to specific applications (holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042) · CPC title