Optical time reversal by ultrasonic encoding in biological tissue
Generating an optical-phase conjugation of ultrasonically-modulated diffuse light emitted by a scattering medium includes illuminating the medium with a light beam from a coherent light source, modulating the diffuse light transmitted through the medium with an ultrasonic wave focused on a region of interest within the medium, and retro-reflectively illuminating the medium using a phase-conjugated copy of the diffuse light that was ultrasonically modulated.
1. A method for generating an optical-phase conjugation of diffuse light emitted by a scattering medium comprising:
illuminating the medium with a light beam from a coherent light source;
ultrasonically modulating the diffuse light transmitted through the medium with an ultrasonic wave focused on a region of interest within the medium; and
retro-reflectively illuminating the medium using a phase-conjugated copy of the diffuse light that was ultrasonically modulated.
2. A method in accordance with claim 1 , wherein the coherent light source comprises a continuous-wave laser.
3. A method in accordance with claim 1 , further comprising transmitting the ultrasonic wave to the medium using at least one ultrasonic transducer.
4. A method in accordance with claim 1 , further comprising holographically recording an interference pattern between the diffuse light emitted by the medium and a first reference light beam.
5. A method in accordance with claim 4 , further comprising reading the hologram using a second reference light beam comprising a phase conjugate of the first reference light beam.
6. A method in accordance with claim 1 , further comprising collecting the diffuse light using an optical assembly.
7. A method in accordance with claim 1 , further comprising using a modulator to frequency shift the light beam from the light source by an amount equal to a central frequency of the ultrasonic wave.
8. An imaging system comprising:
a continuous wave laser to emit a light beam and to illuminate a scattering medium such that diffuse light is emitted by the medium in response to the light beam;
an ultrasonic transducer to modulate the diffuse light transmitted through the medium with an ultrasonic wave focused on a region of interest within the medium;
a photorefractive device to create a phase-conjugated copy of the ultrasonically-modulated diffuse light and to illuminate the medium using the phase-conjugated light that converges to a focal zone of the ultrasonic wave; and
a computer to control emission of the light beam by the laser.
9. An imaging system in accordance with claim 8 , wherein the ultrasonic transducer comprises an array of ultrasonic transducers.
10. An imaging system in accordance with claim 8 , wherein the photorefractive device records an interference pattern between the ultrasonically-modulated diffuse light emitted by the medium and a first reference light beam.
11. An imaging system in accordance with claim 10 , wherein the photorefractive device further reads the hologram using a second reference light beam that is a phase conjugate of the first reference light beam.
12. An imaging system in accordance with claim 8 , further comprising an optical assembly to collect the diffuse light.
13. An imaging system in accordance with claim 8 , further comprising a modulator to frequency shift the light beam from the laser by an amount equal to a central frequency of the ultrasonic wave.
14. An imaging system in accordance with claim 8 , wherein the imaging system comprises one of a transmission-mode fluorescence imaging system and a reflection-mode fluorescence imaging system.
15. An apparatus for use with an imaging system, the apparatus comprising:
a continuous wave laser to emit a light beam and to illuminate a scattering medium such that diffuse light is emitted by the medium in response to the light beam;
an ultrasonic transducer to modulate the diffuse light transmitted through the medium with an ultrasonic wave focused on a region of interest within the medium; and
a photorefractive device to create a phase-conjugated copy of the ultrasonically-modulated diffuse light and to illuminate the medium using the phase-conjugated light that converges to a focal zone of the ultrasonic wave.
16. An apparatus in accordance with claim 15 , wherein the photorefractive device records an interference pattern between the ultrasonically-modulated diffuse light emitted by the medium and a first reference light beam.
17. An apparatus in accordance with claim 16 , wherein the photorefractive device further reads the hologram using a second reference light beam that is a phase conjugate of the first reference light beam.
18. An apparatus in accordance with claim 15 , further comprising an optical assembly to collect the diffuse light.
19. An apparatus in accordance with claim 15 , further comprising a modulator to frequency shift the light beam from the laser by an amount equal to a central frequency of the ultrasonic wave.
20. An apparatus in accordance with claim 15 , wherein the apparatus comprises one of a transmission-mode fluorescence microscope and a reflection-mode fluorescence microscope.