A Caltech Library Service

Seeing Through the Fog: Using Scattered Light to Peer Deeper into Biological Tissue


Brake, Joshua Harris (2019) Seeing Through the Fog: Using Scattered Light to Peer Deeper into Biological Tissue. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0PP8-2E39.


Optical scattering is a fundamental problem in biomedical optics and limits most optical techniques to shallow operating depths less than 1 millimeter. However, although the scattering behavior of tissue scrambles the information it contains, it does not destroy it. Therefore, if you can unscramble the scattered light, it increases the accessible imaging depths up the absorption limit of light (several centimeters deep).

One such way to beat optical scattering is using wavefront shaping. Borrowing ideas from adaptive optics in astronomy and phased arrays in radar and ultrasonic imaging, the basic concept of wavefront shaping is to control the phase and amplitude of the light field in order to harness scattered light. Using wavefront shaping techniques, scattered light can be used to form focal spots or transmit information through or inside optically scattering media. Furthermore, even without correcting for scattering directly by shaping the input light field, the properties of the scattered light can be analyzed to recover information about the structure and dynamic properties of a sample using methods from diffuse optics.

The main contributions of this thesis are along these two lines of research: moving wavefront shaping toward more practical applications and developing new techniques to recover useful physiological information from scattered light. This is developed through three main projects: (1) an investigation of how dynamic samples impact the scattering process and the practical implications of these dynamics on wavefront shaping systems, (2) the development of a wavefront shaping system combining light and ultrasound to focus light inside acute brain slices to improve light delivery for optogenetics, (3) a novel method to sensitively detect the dynamics of scattered light and use it to tease out information about the flow of blood within the tissue sample of interest.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:biomedical optics; wavefront shaping; light scattering; biphotonics; speckle visibility spectroscopy; diffuse correlation spectroscopy
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Yang, Changhuei
Thesis Committee:
  • Wang, Lihong (chair)
  • Yang, Changhuei
  • Emami, Azita
  • Gradinaru, Viviana
  • Chung, Euiheon
Defense Date:17 May 2019
Non-Caltech Author Email:josh (AT)
Funding AgencyGrant Number
National Institutes of Health (NIH)DP2OD007307
National Institutes of Health (NIH)U01NS090577
National Institutes of Health (NIH)F31EB021153
Gwangju Institute of Science and Technology–California Institute of Technology (Caltech) Collaborative Research ProgramCG2012
Donna and Benjamin M. Rosen Bioengineering CenterUNSPECIFIED
Record Number:CaltechTHESIS:05282019-104728085
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for chapter 2 adapted for chapter 3 adapted for chapter 4
Brake, Joshua Harris0000-0002-5113-6886
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11551
Deposited By: Joshua Brake
Deposited On:31 May 2019 21:57
Last Modified:08 Nov 2023 18:41

Thesis Files

PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page