Improving the axial resolution in time-reversed ultrasonically encoded (TRUE) optical focusing with dual ultrasonic waves

Qiang Yang, Xiao Xu, Puxiang Lai, Xinzhu Sang, Lihong V. Wang

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

1 Citation (Scopus)


Focusing light inside highly scattering media beyond the ballistic regime is a challenging task in biomedical optical imaging, manipulation, and therapy. This challenge can be overcome by time reversing ultrasonically encoded (TRUE) diffuse light to the ultrasonic focus inside a turbid medium. In TRUE optical focusing, a photorefractive crystal or polymer is used as the phase conjugate mirror for optical time reversal. Accordingly, a relatively long ultrasound burst, whose duration matches the response time of the photorefractive material, is used to encode the diffuse light. With this long ultrasound burst, the resolution of the TRUE focus along the acoustic axis is poor. In this work, we used two transducers, emitting two intersecting ultrasound beams at 3.4 MHz and 3.6 MHz respectively, to modulate the diffuse light within their intersection volume at the beat frequency. We show that light encoded at the beat frequency can be time-reversed and converge to the intersection volume. Experimentally, TRUE focusing with an acoustic axial resolution of ∼1.1 mm was demonstrated inside turbid media, agreeing with the theoretical estimation.
Original languageEnglish
Title of host publicationPhotons Plus Ultrasound
Subtitle of host publicationImaging and Sensing 2014
ISBN (Print)9780819498564
Publication statusPublished - 1 Jan 2014
Externally publishedYes
EventPhotons Plus Ultrasound: Imaging and Sensing 2014 - San Francisco, CA, United States
Duration: 2 Feb 20145 Feb 2014


ConferencePhotons Plus Ultrasound: Imaging and Sensing 2014
Country/TerritoryUnited States
CitySan Francisco, CA


  • Axial resolution
  • Optical imaging
  • Optical phase conjugation
  • Photorefractive crystal
  • Time-reversed ultrasonically encoded (TRUE) optical focusing
  • Tissue optics

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Radiology Nuclear Medicine and imaging


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