NewsEtc., March, 1998. Steven Jacques, Oregon Medical Laser Center
This month we emphasize polarized light in turbid media.
The purposes of this gallery are:
Links are provided to the websites and viewers are encouraged to visit the original sites which have more pictures, discussions, references to papers, job opportunities, software, lists of staff, etc.
A polarized HeNe laser was directed down onto a cup filled with dilute Intralipid, an aqueous suspension of lipid droplets. A CCD video camera viewed the liquid surface slightly off axis so as to avoid the specular reflectance of the laser source from the surface. Two images were acquired, one image with an analyzing polarizer filter oriented parallel to the polarization of the source and one image with the polarizer oriented perpendicular. The difference in images yielded a pattern that emphasized the polarized light and rejected any randomly polarized light commong to both images.
How polarized light spreads in turbid medium.In 1996, a masters student at Rice University (Dawn Stephens), my colleague at MD Anderson Cancer Center (Lihong Wang, now at Texas A&M Univ.) and I began working on how polarized light reflected from scattering media. An old optics problem, nevertheless the beauty of the images fascinated us all. Another graduate student in our laboratory visiting from the Univ. of Hannover, Germany, (Martin Ostermeyer) also contributed. Yet another student in our laboratory from Rice Univ. (Andreas Hielscher) was so fascinated that when he graduated and moved to Los Alamos National Laboratory, he took up the imaging of polarized light as well (see images below). Now, in Oregon, we have extended the work to develop a video camera using polarized light to visualize cancer margins in the skin.
|Oregon Medical Laser Center.|
Prepared by Ken Lee M.D. with help from Gary Gofstein, John Viator, and Steven Jacques.
A polarized HeNe laser is directly through a small hole in a mirror down onto the turbid medium. The reflected light is reflected off the mirror toward the imaging system. A small disk (central yellow circle in image) held by a thin wire blocks the directly backscattered HeNe beam. These images are of polystyrene spheres (204 nm dia., 0.05% concentration by weight, mus' = 1.9 cm^-1) suspended in water. In the left image, the incident beam was linearly polarized at +45 degrees with respect to the x-axis and the analyzer consisted of a linear polarizer oriented along the y-axis. The right image was obtained with a right-hand circularly polarized incident beam and the linear polarization analyzer was oriented along the x-axis. These are not difference images like the picture above.
Diffuse backscatter of polarized light in highly scattering media.This image is from the front cover of a special issue of Optics Express (Vol. 1, No. 13, Dec. 22, 1997) focusing on biomedical optics. The image shows how polarized light spreads in a turbid light-scattering medium from the entry point of a polarized HeNe laser. This article reports the variety of images based on the Mueller Matrix whose elements are derived from images with various choices of orientation of linearly polarized light or directions of circularly polarized light or total light for the light source and the detection camera. Andreas Hielscher, Judith Mourant and colleagues are investigating the patterns of polarized light reflectance from solutions of normal and malignant cells.
|Los Alamos National Laboratory|
Diffuse backscattering Mueller matrices of highly scattering media. Andreas H. Hielscher, Angelia A. Eick, Judith R. Mourant, Dan Shen, James P. Freyer and Irving J. Bigio. Optics Express Vol. 1, No. 13, p. 441-453, Dec. 22, 1997.