Imaging polarimetry has emerged over the past three decades as a powerful tool to enhance the information available in a variety of remote sensing applications. We discuss the foundations of passive imaging polarimetry, the phenomenological reasons for designing a polarimetric sensor, and the primary architectures that have been exploited for developing imaging polarimeters. Considerations on imaging polarimeters such as calibration, optimization, and error performance are also discussed. We review many important sources and examples from the scientific literature.

/pdf/review-of-passive-imaging-polarimetry-for-remote-sensing-3kk5ut05ha.pdf

Review of passive imaging polarimetry for remote sensing applications

We describe the design, construction, alignment, and calibration of a photometric ellipsometer of the rotating-analyzer type Data are obtained by digital sampling of the transmitted flux with an analog-to-digital converter, followed by Fourier transforming of the accumulated data with a dedicated minicomputer With an operating mechanical rotation frequency of 74 Hz, a data acquisition cycle requires less than 7 msec The intrinsic precision attainable is high because precision is limited only by shot noise or intrinsic source instabilities, even when relatively weak continuum lamps are used as light sources Precision may be improved by accumulating the data for consecutive cycles at a fixed wavelength The system allows complex reflectance ratios to be determined as continuous functions of wavelength from the near infrared to the near ultraviolet spectral range Data reduction programs can be modified to calculate complex refractive index or dielectric function spectra, or film thicknesses and refractive indices, as well as the usual ellipsometric parameters tanpsi, cosDelta

High Precision Scanning Ellipsometer

The application of reciprocity principles in optics has a long history that goes back to Stokes, Lorentz, Helmholtz and others. Moreover, optical applications need to be seen in the context of applications of reciprocity in particle scattering, acoustics, seismology and the solution of inverse problems, generally. In some of these other fields vector wave propagation is, as it is in optics, of the essence. For this reason the simplified approach to light wave polarization developed by, and named for, Jones is explored initially to see how and to what extent it encompasses reciprocity. The characteristic matrix of a uniform dielectric layer, used in the analysis of interference filters and mirrors, is reciprocal except when the layer is magneto-optical. The way in which the reciprocal nature of a characteristic matrix can be recognized is discussed next. After this, work on the influence of more realistic attributes of a dielectric stack on reciprocity is reviewed. Some of the numerous technological applications of magneto-optic non-reciprocal media are identified and the potential of a new class of non-reciprocal components is briefly introduced. Finally, the extension of the classical reciprocity concept to systems containing components that have nonlinear optical response is briefly mentioned.

https://iopscience.iop.org/article/10.1088/0034-4885/67/5/R03/pdf

Reciprocity in optics

Polarimetry has a long and successful history in various forms of clear media. Driven by their biomedical potential, the use of the polarimetric approaches for biological tissue assessment has also recently received considerable attention. Specifically, polarization can be used as an effective tool to discriminate against multiply scattered light (acting as a gating mechanism) in order to enhance contrast and to improve tissue imaging resolution. Moreover, the intrinsic tissue polarimetry characteristics contain a wealth of morphological and functional information of potential biomedical importance. However, in a complex random medium-like tissue, numerous complexities due to multiple scattering and simultaneous occurrences of many scattering and polarization events present formidable challenges both in terms of accurate measurements and in terms of analysis of the tissue polarimetry signal. In order to realize the potential of the polarimetric approaches for tissue imaging and characterization/diagnosis, a number of researchers are thus pursuing innovative solutions to these challenges. In this review paper, we summarize these and other issues pertinent to the polarized light methodologies in tissues. Specifically, we discuss polarized light basics, Stokes-Muller formalism, methods of polarization measurements, polarized light modeling in turbid media, applications to tissue imaging, inverse analysis for polarimetric results quantification, applications to quantitative tissue assessment, etc.

/pdf/tissue-polarimetry-concepts-challenges-applications-and-4fp6pfuwhm.pdf

Tissue polarimetry: concepts, challenges, applications, and outlook

• We describe a new technique for the measurement of retinal nerve fiber layer thickness and compare its results with histopathologic measurements in the same eyes. For these studies, two fixed monkey eyes were incised and placed on a pedestal in a plastic viewing dish. The eyes were perfused to maintain a pressure between 10 and 20 mm Hg. An ellipsometer, an optical device used to measure the change in polarization of light (retardation), was implemented in a laser tomographic scanner to obtain polarization data from the two monkey retinas. For the 15 measured locations, retardation ranged between a mean (± SD) of 0.9° ± 1.8° and 23.7° ± 0.3°. Subsequently, retinal nerve fiber layer thickness was measured at the imaged points in epoxy resin-embedded sections by an observer masked to the ellipsometry data. These values ranged between 20.4 μm and 213.9 μm. There was an excellent correlation (R =.83) between retardation and the histopathologic measurement of retinal nerve fiber layer thickness. Quantitating retinal nerve fiber layer thickness may enhance discrimination between glaucomatous and normal eyes earlier than is currently available by anatomic and functional approaches.

Histopathologic Validation of Fourier-Ellipsometry Measurements of Retinal Nerve Fiber Layer Thickness

Conditions for achieving equal and opposite angular deflections of a light beam by reflection and refraction at an air-dielectric boundary are determined. Such angularly symmetric beam splitting (ASBS) is possible only if the angle of incidence is >60° by exactly one third of the angle of refraction. This simple law, plus Snell's law, leads to several analytical results that clarify all aspects of this phenomenon. In particular, it is shown that the intensities of the two symmetrically deflected beams can be equalized by proper choice of the prism refractive index and the azimuth of incident linearly polarized light. ASBS enables a geometrically attractive layout of optical systems that employ multiple prism beam splitters.

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary: reply.

Surface roughness and optical contact characterization of transparent prisms using frustrated total internal reflection tunneling ellipsometry

A quarter-wave layer (QWL) of high refractive index, which is deposited on a transparent prism of low refractive index, can be designed to split an incident p-polarized light beam at the Brewster angle (BA) of the air–substrate interface into p-polarized reflected and transmitted beams of equal intensity (50% each) that travel in orthogonal directions. For reflection of p-polarized light at the BA, the supported QWL functions as a free-standing (unsupported) pellicle. An exemplary design is presented that uses SixGe1−x QWL deposited on an IRTRAN1 prism for applications (such as Michelson and Mach–Zehnder interferometry) with a variable compositional fraction x in the 2–6 μm mid-IR spectral range.

Brewster-angle 50%-50% beam splitter for p-polarized infrared light using a high-index quarter-wave layer deposited on a low-index prism.

The change of Polarization of light upon reflection from an optically isotropic film -substrate system is determined by the ratio of complex amplitude p and s reflection coeffi- cients, p = Rp /R . If the incident light is linearly polarized at 45° azimuth from theplane of incidene, p assumes the dual role of representing the elliptic vibration of thereflected light. We examine p as a function of angle of incidence and film thickness dfor the SiO2 -Si system at wavelength X = 6328 R and present contours of c = constant andd = constant in the complex p plane. Conversely, we also determine contours in the q(1plane that represent ip = arctan Ipl= constant and A =arg p= constant. Of particular interestare images in the clpd plane of the real and imaginary axes (A =O, r and A = +4) and of the unitcircle(= y) of the complex p plane.IntroductionConsider the oblique reflection at an angle of a light beam by a film- substrate system, Fig. 1. Media 0, 1, and 2 represent the ambient, film and substrate, respectively, whichare all assumed to be homogeneous and isotropic. The film has parallel plane boundaries andis of thickness d. p and s indicate the linear polarization directions parallel and perpen-dicular to the plane of incidence. The complex- amplitude reflection coefficients for thesetwo Polarizations are given byl

Characteristics Of Polarized Light Reflection From The Si0 2 -Si Film-Substrate System

We describe efficient beam splitters for the equi-partition of infrared input power using combined reflection and transmission by a strip-coated all-dielectric slab. Because no metal coating is used, high efficiency is achieved. The beam splitters use a fused silica parallel-slab that is strip coated with germanium on the front and back sides. Specific designs for operation at 1.55, 2.02 and 5.0 µm wavelengths are presented.

Rasheed M. A. Azzam

Papers

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary: reply.

Surface roughness and optical contact characterization of transparent prisms using frustrated total internal reflection tunneling ellipsometry

Brewster-angle 50%-50% beam splitter for p-polarized infrared light using a high-index quarter-wave layer deposited on a low-index prism.

Characteristics Of Polarized Light Reflection From The Si0 2 -Si Film-Substrate System

High-efficiency all-dielectric strip-coated beam splitters for the equipartition of infrared input power