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Method of Characterizing Optical Systems that Depolarize Light

IP.com Disclosure Number: IPCOM000088979D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 22K

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The described method provides a complete determination of the polarization-altering properties (including depolarization) of a linear optical system.

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Method of Characterizing Optical Systems that Depolarize Light

The described method provides a complete determination of the polarization- altering properties (including depolarization) of a linear optical system.

An automated ellipsometer accomplishes a complete determination of the polarization state, as well as the intensity, of a beam of light. This permits unambiguous measurements of Delta for ellipsometric applications. Also, it determines the degree of polarization (fraction of the light that is polarized, as distinguished from unpolarized or natural light), which ellipsometers in general cannot do. All the polarization-altering properties of a linear optical system may thus be determined (including depolarization). Additionally, since intensity is also measured, absolute reflectance or transmittance may be found in the same measurement.

The areas of application unique to these added capabilities include reflection from rough surfaces, transmission through suspensions of small particles, opalescent materials, and similar instances where scattering processes are important. The amount of depolarization can then be correlated with average particle size, average surface roughness, etc., in terms of the measurement wavelength.

The wavelength range need not be limited to the invisible region. Ellipsometry has been carried out in the radio wave, microwave, infrared, ultraviolet and up to the X- and gamma ray regions of the spectrum. For example, moisture content and average height of soil and vegetation as well as wave height and salinity of sea water have been investigated via airborne microwave ellipsometry. The present system can be implemented in these wavelength regions, as well as in the invisible, and add a new dimension to these studies.

The procedure is best described in terms of the four-element Stokes vector S to represent the state of polarization of a beam of light and and the four-by-four Meuller matrix M to represent the effect of a linear optical system interacting with the light to produce an outgoing beam with Stokes vector S': S' = MS (1) All the optical properties (at the measurement wavelength and direction of travel of incident and outgoing light) of optical system are deducible from the 16 elements of M. The experimental arrangement can be tailored to obtain the desired wavelength and input and output directions.

One procedure to obtain the elements of M under the desired experimental conditions is by using a polarizer and compensator following the light source, whereby a series of four incident polarization states, having linearly independent Stokes vectors, is produced. Using the rotating-compensator plus analyzer in front of the detector, the Stokes vectors of the correspond...