The purpose of this application is to use phase modulated light to see an object clearly through a surrounding turbid media. The photoelastic modulator is used to detect, nearly instantaneously, the difference in scattering of two orthogonal states of linear or circular polarization.
AN EXAMPLE OF ONE TYPICAL SETUP
Light from the laser passes a chopper and polarizer and the PEM; it is then scattered by both the turbid medium and the embedded target of the sample. The scattered light is synchronously detected by a photomultiplier and lock-in amplifiers. If the linear or circular intensity difference (LID or CID) of light returned by the embedded object differs from that scattered by the surrounding turbid medium, then scanning a light source across the sample will yield an intensity profile that varies in correspondence with structural features of the target.
The PEM must be set to a retardation A0 = 2.405 radians (.383 waves) where the Bessel function J0(A0) = 0.
Lock-in amplifiers detect both the 1st and 2nd harmonic from the PEM.
TYPICAL HEAD ASSEMBLIES
Non-invasive Detection of Subcutaneous Malignancies, Remote Monitoring of Soil Conditions, Health of Arboreal Canopies, Visual Penetration of Clouds, Aerosols, Seawater, Skin, and Blood
M. P. Silverman and Wayne Strange, “Light Scattering from Optically Active and Inactive Turbid Media,” Optics and Imaging in the Information Age (Society for Imaging Science and Technology, Springfield VA, 1996) 173-180.
M. P. Silverman, W. Strange, J. Badoz, and I. A. Vitkin, “Enhanced Optical Rotation and Diminished Depolarization in Diffusive Scattering from a Chiral Liquid,” Optics Communications 132 (1996) 410-416.
Contact us for additional information on using PEMs in scattering applications.