Coherence and polarization of light propagating through scattering media and biological tissues

Abstract

The degree of polarization of light propagating through scattering media was measured as a function of the sample thickness in a Mach-Zehnder interferometer at a wavelength of lambda = 633 nm. For polystyrene microspheres of diameters 200, 430, and 940 nm, depolarization began to appear for thicknesses larger than 23, 19, and 15 scattering mean free paths (SMFP's), respectively, where the coherently detected scattered component dominates the ballistic component. For large particles (940 nm) the initial polarization survived partially in the scattering regime and progressively vanished up to the detection limit of our setup. This phenomenon was similarly observed in diluted blood from 12.5 to 280 SMFP's. Beyond this thickness the fluctuating parallel and crossed components of polarization became random. A dual-channel interferometer allowed us to detect simultaneously the low-frequency fluctuations of both polarized components through a few millimeters in liver tissue.

Polarised stereo endoscope and narrowband detection for minimal access surgery

“…The CR channel provides depth gating by rejecting the polarisation-maintaining specularly or superficially-reflected light and detecting the multiply scattered randomly-polarised signal. In the CO channel this diffusely reflected signal is also present, along with specularly reflected light, which retains its initial polarisation direction and photons that have penetrated the surface but have undergone a very small number (less than 10) of scattering events before reemerging [16]. The depths from which these superficial photons may be detected is therefore dependant on the scattering properties of the tissue and the wavelength of the light used.…”

Tissue characterization with ballistic photons: counting scattering and/or absorption centres

“…Biomedical diagnosis is often based on the characterization of tissue samples using the optical tech− niques, such as the response to the coherent or non-coherent illumination, including reflection (optical coherence tomog− raphy), transmission [4,5], absorption, and scattering [6][7][8][9], in either time−integrated or time−resolved applications [10][11][12][13][14][15].…”

Contrast improvement in scattered light confocal imaging of skin birefringent structures by depolarization detection

“…These reports describe randomization of polarization as polarized light propagates through biological tissues. The intensity of the light detected from the subsurface structures can be emphasized or rejected using an analyzing polarizer with different polarization orientations [15][16][17]. Jacques et al demonstrated that the image based on polarization ratio of two images acquired through an analyzing linear polarizer oriented parallel and perpendicular to the polarization of illumination can emphasize the imaging of superficial skin structures [14].…”