Weak value amplification of an optical Faraday differential refraction effect

In the presence of a longitudinal magnetic field B, a beam of linearly polarized light incident from a Faraday medium of Verdet constant V refracts at its interface with a medium of negligible Verdet constant and emerges as two opposite circularly polarized beams that are separated by a small divergence angle δ that is proportional to the product BV. Judicious postselection of the polarization state of the emergent light can be used to amplify the measured value of δ by several orders of magnitude. This technique makes it possible to optically measure either very small V values when B is known or small magnetic fields when V is known.     

Investigation of the polarization optics of the living human cornea and lens with purkinje images

We present what to our knowledge is a new method for assessing the polarization optics of the cornea and lens, by examining the state of polarization of the first, second, and fourth Purkinje images. When linearly polarized light is incident on the cornea at 70 degrees to the line of gaze along the horizontal meridian, and then traverses the cornea, or the cornea and the lens, the emergent light is elliptically polarized. The degree of ellipticity varies widely between subjects. The results indicate that both the cornea and the lens may be optically active and to our knowledge are the first to suggest that the cornea may exhibit circular birefringence.     

Detection of biological particles by the use of circular dichroism measurements improved by scattering theory

Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.     

All-optical controlling of the focal intensity of a liquid crystal polymer microlens array

The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an all-optically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.     

Optical properties of an isotrophic optically active medium at oblique incidence

The optical properties of an isotropic optically active medium at oblique incidence have been investigated. It was found that the amount of transmitted light converted from p polarization to s polarization and vice versa, through an isotropic optically active medium, is independent of the state of incident polarization. Though the optical rotation through the optically active medium is same for p and s polarization at normal incidence, it becomes different at oblique incidences.     

Two-dimensional polarization encoding with a phase-only liquid-crystal spatial light modulator

We show how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM). Each pixel of the LCSLM acts as a voltage-controlled wave plate and can be programmed over a 2pi phase range at a wavelength of 514.5 nm. Techniques are reviewed for either rotating the major axis of elliptically polarized light or for converting an input linearly polarized beam into an arbitrary elliptically polarized beam. Experimental results are demonstrated in which we generate various two-dimensional spatial patterns of polarized light. Several potential applications are suggested. We also report an unexpected edge-enhancement effect that might be useful in image processing applications.     

Polarization properties of inversely twisted nematic liquid-crystal gratings

Based on the Jones matrix representation of twisted nematic liquid crystals (LC's), we have carried out a theoretical analysis of the polarization properties of inversely twisted nematic (ITN) LC gratings. Some interesting polarization behaviors are expected in the ITN LC grating. When a linearly polarized light parallel or perpendicular to the grating direction is incident on the ITN LC grating, the diffracted light in the 0th order is linearly polarized with the same polarization direction of incident light, while the diffracted light in high orders is linearly polarized perpendicular to that of incident light. Using a multirubbing alignment technique, we have practically prepared an ITN LC grating with ?45 degrees inversely twisted structures. The experimental investigations of the optical characteristics of the ITN LC grating demonstrate agreement with theoretical expectations.     

Collimation testing with optically active materials

A novel method to test the collimation of laser beams with optically active mediums and a pair of crossed polarizers is presented. Optically active materials rotate the plane of polarization of incident plane-polarized light. A decollimated laser beam passing through such a material will experience a greater effective thickness than a collimated laser beam, resulting in greater outputs. In this method the output intensity variation is related to the amount of decollimation of the incident beam, and the method does not require any referencing or fringe analysis and is easy to implement.     

High-Quality Brewster's Angle Polarizer for Broadband Infrared Application

We have designed and constructed a linear polarizer for use with visible and infrared radiation. The broadband polarizer consists of four germanium plates arranged in a chevron geometry. Input radiation is incident near Brewster's angle for the first plate such that the reflected beam is preferentially s-wave polarized. This reflected beam is steered subsequently to the successive plates, always intersecting near Brewster's angle. The beam polarization at the output of the device is almost completely s-wave polarized. The ratio of the paraxial flux of the nearly extinguished p-wave polarized light to the s-wave polarized light transmitted through the device is found to be less than 10(-5) for laser illumination at wavelengths of 0.633, 1.32, 3.39, and 10.6 mum. Calculations predict that extinction ratios less than 10(-5) are achievable over the wavelength range from 0.4 mum to beyond 500 mum. Alternative design geometries involving fewer plates are also described along with their advantages and disadvantages.     

Optically Active Fabry-Perot Etalon

Abstract

The paper studies multibeam interference in the case of multiple reflection of an electromagnetic wave (EMW) from a plane-parallel, isotropic, optically active and non-absorbing plate (Fabry-Perot etalon). Due to the optical activity the two refracted EMW in the plate are left- and right-circularly polarized and have unequal refractive indices. During their propagation through the plate the two waves accumulate a phase difference which modulates the multibeam interferogram. Both in the reflected and in the transmitted beams a polarization perpendicular to the polarization of the incident EMW appears (whose intensity is up to several tens of per cent of the incident beam intensity). Due to the gyrotropy of the plate at large angles of incidence the interference bands split. Thus the optical activity of the etalon may affect its precision as an optical element. The multibeam interference may be used as a source of spectroscopic information about the optical activity of the plate.     

Spatial light modulator-controlled alignment and spinning of birefringent particles optically trapped in an array

We demonstrate the use of a phase-only liquid-crystal spatial light modulator (SLM) for polarization-controlled rotation and alignment of an array of optically trapped birefringent particles. A collimated beam incident upon a two-dimensional lenslet array yields multiple foci, scaled to produce optical gradient traps with efficient three-dimensional trapping potentials. The state of polarization of each trapping beam is encoded by the SLM, which acts as a matrix of wave plates with computer-controlled phase retardations. Control of the rotation frequency and alignment direction of the particles is achieved by the transfer of tunable photon spin angular momentum.     

Magnetometry in dense coherent media

The rotation of the polarization direction of linearly polarized light produced by the nonlinear magneto-optic effect has been proposed as a sensitive measure of small magnetic fields. In this paper, the advantages of this technique in optically thick media for precision magnetometry are discussed. Results are presented for measurements of this rotation for resonant light in optically dense Rb vapour under various conditions, with and without buffer gas. The sensitivity of the measurements of small magnetic field is investigated as a function of laser frequency, laser power, beam diameter and atomic density for D ₁ line of ⁸⁷Rb.     

Spin-to-orbit conversion at acousto-optic diffraction of light: conservation of optical angular momentum

Acousto-optic diffraction of light in optically active cubic crystals is analyzed from the viewpoint of conservation of optical angular momentum. It is shown that the availability of angular momentum in the diffracted optical beam can be necessarily inferred from the requirements of angular momentum conservation law. As follows from our analysis, a circularly polarized diffracted wave should bear an orbital angular momentum. The efficiency of the spin-to-orbit momentum conversion is governed by the efficiency of acousto-optic diffraction.     

The intertwined history of polarimetry and ellipsometry

Ellipsometry and reflection polarimetry are almost synonymous. Therefore it is not surprising that ellipsometry and polarimetry share a common history which is that of optical polarization. The discoveries in the late 1600s by Bartholinus and Huyghens of double refraction by Iceland spar and the unusual properties of the twin beams thus generated presented insurmountable difficulties for the entrenched corpuscular-ray theory of Newton and caused research on polarization to remain stagnant in the 1700s. Major breakthroughs came in the early 1800s when Malus discovered polarization of light by reflection and his cosine-squared law and Fresnel and Arago enunciated their laws of interference of polarized light that helped establish the transverse vector nature of luminous vibrations. Important further research immediately followed on optical rotatory power by Arago, Biot, and Pasteur that ushered fundamental and practical applications of polarimetry in chemistry and biology. Fresnel deserves to be recognized as a founder of ellipsometry by virtue of his laws of reflection of polarized light at interfaces between dissimilar media and his identification and production of circular and elliptical polarization. The later part of the 19th century witnessed significant discoveries of magneto-optic and electro-optic effects by Faraday, Kerr, and Pockels that greatly enriched polarization optics and physics. The 1896 discovery of the Zeeman effect launched the exciting field of solar polarimetry. The 1864 crown achievement of Maxwell's electromagnetic (EM) theory provided a unified framework for the analysis of polarization phenomena across the entire EM spectrum.     

Double refraction of a Gaussian beam into a uniaxial crystal

For a linearly polarized three-dimensional Gaussian beam in air that is normally incident upon a plane interface with a uniaxial crystal with optic axis in an arbitrary direction, we present integral representations for the transmitted field suitable for asymptotic analysis and efficient numerical evaluation and derive analytical expressions for transmitted nontruncated Gaussian beams for the cases in which the incident beam is polarized parallel to the plane containing the optic axis and the interface normal and transverse to it. The general solution for an arbitrary polarization state of an incident Gaussian beam follows by superposition of these two solutions.     

Polarization changes in a partially coherent radially polarized doughnut beam through turbulent ocean

On the basis of the extended Huygens–Fresnel integral principle and unified theory of coherence and polarization of light, we studied the effects of oceanic turbulence on polarization properties of a partially coherent radially polarized doughnut (PCRPD) beam. The ocean-induced fluctuations in the refractive index are assumed be driven by temperature and salinity fluctuations. Numerical examples of changes in polarization properties, such as the degree of polarization, the degree of ellipticity, and the orientation angle in the oceanic turbulence for the PCRPD beam, are given. Our analysis demonstrates how polarization of the PCRPD beam is affected by statistical properties of the source and by several parameters of oceanic turbulence. We find that the propagation of the PCRPD beam is different from that of stochastic beams in oceanic turbulence. The degree of polarization for the PCRPD beam approaches a certain steady value, and the elliptical polarized state of the fully polarized portion of the beam will become fully linear in the far field.     

Polarization effects on scatterer sizing accuracy analyzed with frequency-domain angle-resolved low-coherence interferometry

Angle-resolved low-coherence interferometry (a/LCI) enables us to make depth-resolved measurements of scattered light that can be used to recover subsurface structural information such as the size of cell nuclei. Endoscopic frequency-domain a/LCI (fa/LCI) acquires data by using a novel fiber probe in a fraction of a second, making it a clinically practical system. However, birefringent effects in fiber-based systems can alter the polarization state of the incident light and potentially skew the collected data. We analyze the effect the polarization state of the incident light has on scattering data collected from polystyrene microsphere tissue phantoms and in vitro cell samples and examine the subsequent accuracy of the determined sizes. It is shown that the endoscopic fa/LCI system accurately determines the size of polystyrene microspheres without the need to control the polarization of the incident beam, but that epithelial cell nuclear sizes are accurately determined only when the polarization state of the incident light is well characterized.     

Fabrication and optical characterization of template-constructed thin films with chiral nanostructure

We report the fabrication of thin films perforated by high aspect ratio helical or chevron pores by an extension of the glancing angle deposition (GLAD) technique. The perforated films were created by transferring the nanostructure of a GLAD template film into target materials such as polymers and spin-on-glasses and subsequently removing the template. The pore shapes are shown to be highly controllable and films designed to suit particular applications are discussed. By a double templating technique, we replicate the structure of the original film using alternate materials, which are typically less suited to the unmodified GLAD technique. Helical films of Cu and Ni were created by this method and the process should be transferable to additional electrodeposited materials. The optical rotatory power of perforated thin films formed on glass substrates was characterized and perforated films were shown to be effective in rotating the polarization plane of linearly polarized incident light by as much as 1.4/spl deg///spl mu/m.     

Polarization structure of lidar signals reflected from ice crystal clouds

Polarization characteristics of signals of a monostatic lidar intended for sensing of homogeneous ice crystal clouds are calculated by the Monte Carlo method. Clouds are modeled as monodisperse ensembles of randomly oriented hexagonal ice crystals. The polarization state of multiply scattered lidar signal components is analyzed for different scattering orders depending on the crystal shapes and sizes as well as on the optical and geometrical conditions of observation. Light-scattering phase matrices (SPMs), calculated by the beam splitting method (BSM), are used as input data for solving the vector radiative transfer equation. The principles of the BSM method are briefly described, and the SPM components are given for hexagonal ice plates and columns of different sizes and linearly polarized incident radiation with the wavelength lambda = 0.55 microm.     

Picoliter rheology of gaseous media using a rotating optically trapped birefringent microparticle

An optically trapped birefringent microparticle is rotated by a circularly polarized beam in a confined gaseous medium. By recording the terminal rotation velocity and the change in polarization of the incident trapping beam, we determine the viscosity by probing a picoliter volume of air, carbon dioxide, and argon in the vicinity of the microparticle. We also characterize the optical force acting on a trapped particle in air using the generalized Lorenz-Mie theory taking into account the aberrations present. This opens up a new potential application of optical tweezers for the accurate measurement of gas viscosity in confined geometries.