Showing papers on "Birefringence published in 1972"

Acousto‐optic light deflectors using optical activity in paratellurite

Abstract: Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto‐optic figure of merit in single‐crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this material's birefringence to circularly polarized light. Dixon's equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound‐to‐light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a capacity of 500 linearly resolvable spots with a random access time of 10 μsec, with 50% of the incident light being deflected at 35‐mW acoustic power.

Phase‐matched submillimeter wave generation by difference‐frequency mixing in ZnGeP2

Abstract: Using two step‐tunable CO2 lasers, we have observed phase‐matched generation of frequencies 70 <ν<110 cm−1 by nonlinear mixing in a birefringent ternary semiconductor, ZnGeP2. An observed power of ∼1.7 μW at 83.37 cm−1 gave a signal‐to‐noise ratio of ∼1000 with a Ge:Ga detector. In combination with tunable optical lasers, this technique should yield a tunable source of submillimeter wave radiation for high‐resolution spectroscopy.

Birefringence in dielectric optical waveguides

Abstract: The linear and circular birefringent properties of low-loss single-mode glass fibers are found to depend upon length. Depolarization is about 1 percent/km. Some anomalous behavior can be explained in terms of properties varying locally along the fiber and a resultant upper information rate of over 1012bits/s is estimated. Very small stress distributions or core ellipticities could give rise to the observed effects.

Electrically Controlled Birefringence of Thin Nematic Films

Abstract: This paper reports field‐induced realignment of a nematic liquid crystal. A thin nematic film, which has a negative dielectric anisotropy, is initially homeotropic. Application of a threshold field parallel to the optic axis distorts the nematic ordering and increases the film's birefringence in certain light‐propagation directions. Experimental results are given for threshold voltage, threshold width, optical contrast ratio, frequency response, angular field of view, electrical power consumption, and transient response. Light‐valve applications are described.

Electric‐Field‐Induced Orientational Deformation of Nematic Liquid Crystals: Tunable Birefringence

Abstract: Spatially uniform birefringences tunable over the range 0. 0–0. 15 for applied voltages less than 20 V rms and with a sharp threshold below 4 V rms are obtained for thin layers of nematic liquid crystals with negative dielectric anisotropy. The achievement of spatially uniform tunable birefringence with negative‐dielectric‐anisotropy materials requires a source of in‐plane anisotropy which is provided by a unique previously unreported molecular configuration at zero field. At V=0, the molecules align with their long axes at a small angle to the sample normal. The experimental results are analyzed in terms of a continuum model and experimental values obtained for the relevant elastic constants.

Phase‐matchable nonlinear optical interactions in periodic thin films

Abstract: A proposal for a new method of phase matching in nonlinear optical interactions is made. A periodic perturbation of the surface of a thin‐film waveguide generates space harmonics with new propagation constants which can be phase matched. An analysis of this proposal shows it to be particularly interesting for a class of thin‐film nonlinear devices using the cubic optically isotropic semiconductors (such as GaAs, GaP, etc.) which possess high nonlinear optical coefficients but are not phase matchable by the conventional birefringent techniques.

Théorie quantique des phénomènes de biréfringence electrique et magnétique des molécules

Abstract: A general formalism is set up to apply the variation-perturbation method to the quantum theory of non-linear optical effects, in particular to the electric and magnetic birefringence (Kerr and Cotton-Mouton effects). The quantities describing these effects are obtained from the wave function Ψ of the ground state of the unperturbed molecule and the different vectors and tensors which are determined by a variation method. With this method an approximate computation of the Kerr and Cotton-Mouton constants of some simple molecules has been made.

Optical Generation of Intense Picosecond Electrical Pulses

Abstract: Electrical pulses, 4 A in 10 psec, have been generated by rectification of 1.06‐μm pulses in LiTaO3: Cu++. Their amplitude and duration were measured by photographing the birefringence induced by the pulses propagating along an electro‐optic transmission line illuminated transversely in a Pockel's cell arrangement. The principal mechanism responsible for the generation is the macroscopic polarization resulting from the difference in dipole moment between the ground and excited states of the absorbing Cu++ impurities.

Some aspects of orientation in injection molded objects

Abstract: The birefringences of injection molded plates and the birefringence during steady, isothermal shear flow were compared for some amorphous polymers The materials studied were a polystyrene, a “toughened” polystyrene and an acrylonitrile-butadiene-styrene copolymer The birefringence of the plates, notably the maximum value for the average over the thickness was found to be related to the shear stress at the cavity wall that had occurred during the mold filling process This relationship was independent of temperature To a good approximation, it was also the same as the relationship between the flow birefringence and the shear stress at the wall in isothermal channel flow It thus appears that the anisotropy of injection molded objects is dominated by the shear stresses during the mold filling process regardless of the temperature and of the macroscopic rate of deformation

Thin birefringent polymer films for integrated optics

Abstract: The fabrication of low‐loss (0.1 dB/cm) thin birefringent polymer films on glass substrates is reported. A birefringence of 4.7 × 10−3 was measured in polystyrene. In such films, TE and TM modes can be made degenerate by controlling the film thickness. Degeneracy over distances of up to 3 cm was achieved. Such guides may simplify the construction of modulators and other devices requiring degenerate mode operation.

Design and Performance of a 20-Stage Digital Light Beam Deflector

Abstract: This paper gives optical design considerations and experimental results of a 20-stage digital light beam deflector consisting of a series of nitrobenzene Kerr cells and birefringent calcite prisms. The laser beam is deflected into a two-dimensional raster of 1024 by 1024 positions with a deflection rate of 500 kHz. The optical transmission of the deflector itself is 79% for green laser light. Data about background light and resolution as well as display examples showing alphanumerics and graphics are given.

Nonlinear Optical Properties of Ferroelectric Lead Titanate

Abstract: Optical transmission, refractive‐index, and nonlinear optical properties of single domain PbTiO3 have been measured between room temperature and the Curie temperature Tc. The second‐harmonic coefficient d31 is found to be the highest for any room‐temperature ferroelectric. Since the birefringence is small (approximately 0.008), phase‐matched SHG is not possible, but nondegenerate three‐frequency mixing should be possible. The Miller δ coefficients are analyzed in terms of Jerphagnon's formulation and poor agreement is observed.

Interstellar Circular Polarization

Abstract: This paper shows that optical observations of circular polarization produced by aligned interstellar grains could yield valuable information about the grain material. The interstellar medium is known to be linearly dichroic from observations of interstellar linear polarization. Since the same aligned grains make the medium linearly birefringent, a small component of circular polarization can result from incident linearly polarized light if the position angle of the linear polarization does not coincide with either principal axis of the medium. Calculations demonstrate that the wavelength of the circular polarization is sensitive to the imaginary part of the complex refractive index of the grain material. This provides an opportunity of investigating whether the grains are characteristically dielectric or metallic.

Dynamic mechanical and rheo-optical studies of collagen and gelatin.

Abstract: The frequency dependence of dynamic mechanical properties of rat tail tendon (RTT), enzyme-solubilized collagen membranes (ESC), AKM-23 dialysis membranes, and gelatin film have been measured at 110, 11, and 3.5 Hz from - 160 to 220°C. RTT and AKM-23 are devoid of a rubbery region; there are as many as six mechanical loss transitions. Gelatin and ESC membranes behave as rubbery materials above room temperature; only three tan δE peaks can be resolved for these materials. Strain birefringence was used to measure the crystalline and amorphous contribution of orientation induced by strain. Both the birefringence and the strain optical coefficient are sensitive to the amount of water in a sample. The effect of chemical swelling agents and of annealing on birefringence are described. Stress relaxation data on gelatin film were analyzed with the rubber elasticity theory to give the average number of chains per unit volume, the specific polarizability, the stress-birefringence ratio and the average molecular weight between hydrogen bonds were calculated. The intrinsic amorphous birefringence for “wet” gelatin film is 1.25 × 10−2; it is estimated to be about 6 × 10−2 for “dry” gelatin film.

Domain structure and polarization reversal in films of ferroelectric bismuth titanate

Abstract: A preliminary study has been made of the structure, optical properties and polarization reversal behavior of epitaxial bismuth titanate films grown by sputtering on MgO substrates. As grown, the films are twinned on a coarse scale, with alternate regions oriented with the monoclinic (100) and (010) plane parallel to the (110) MgO surface. Optical birefringence measurements on these regions yielded Δna and Δnb values as a function of temperature which were in general agreement with those measured for bulk crystals. By annealing film sections detached from the substrate, a single orientation of the type (010) was obtained, and regions of such samples could be poled to a single-domain condition. Hysteresis data, with the field applied along the a and c axes, for single domain regions yielded spontaneous polarization results comparable to those reported previously for bulk crystals, but indicated somewhat higher coercive fields. Similar measurements with the field along the [101] axis showed that it is possib...

Light scattering analysis of starch granules

Abstract: Solid state light scattering by starch granules provides a method of determining their average refractive index and the sign of their birefringence. By observing the scattering from a vertically polarized red laser through a parallel analyzer as a function of refractive index of the mounting medium, the theoretically predicted inversion point of the scattering envelope can be seen. Gelatinization in various liquids may also be followed through the change in the scattering as a function of temperature. The experimental data are used to describe the starch granule fine structure in accordance with other data available at present.

The reflected-shadow method for the study of the constrained zones in cracked birefringent media

Abstract: An optical method has been developed for the study of the constrained zones embedded at the crack tips in birefringent materials. Deviation of the partially reflected light beam from the back surface of a thin transparent plate made of a birefringent material, which contained a crack, formed a caustic which defined the constrained zone around the crack tip. The shape of the constrained zone, limited by the caustic, depended on the thickness variation of the plate, as well as on the double refraction of the impinging light beam. It is shown that for an elastically strained birefringent material with a birefringent constant ξ the caustic has the shape of a curve depending on ξ, which for ξ ↑ 0 degenerates to a circle. This curve, when projected on a screen, forms a generalized epicycloid created by the tips of the resultant vector, which represents the reflected and optically deviated light rays. The characteristic properties of the epicycloids are discussed and their connection with the stress inte...

Electric and hydrodynamic properties of polypeptides in solution. III. Aggregation of poly(L‐glutamic acid) in aqueous methanol solvents studied by electric birefringence

Abstract: The rise and decay of electric birefringence for poly(L-glutamic acid) (PLGA) in aqueous solvents containing 20 and 10 vol % methanol have been found to be unusual. The decay curves have been analyzed on the assumption that there exist two kinds of particles, namely, one (component I) with a shorter relaxation time exhibiting positive birefringence and the other (component II) with a longer relaxation time exhibiting negative birefringence at low fields. From the field strength dependence of the steadystate birefringence the permanent dipole moment, the anisotropy of electric polarizability, and the saturation value of birefringence have been determined for each component. Furthermore, from the relaxation time the length of component I and the diameter of component II have been computed on the models of cylindrical rod and oblate ellipsoid, respectively. The dipole moment, the anisotropy of electric polarizability, and the relaxation time of component II are much larger than those of component I. Both the anisotropy of electric polarizability and the optical anisotropy factor are positive in sign for component I and negative for component II. It is concluded that component I is the helical PLGA molecule itself and component II is the side-by-side (antiparallel) aggregate composed of many helical PLGA molecules. The optical anisotropy factor of each component has been discussed on the basis of Peterlin-Stuart theory.

Nonlinear optical and electro-optical properties of dielectrics and ferroelectrics†

Abstract: The article is intended as a review of significant theoretical and experimental achievements in the study of the optical and electro-optical properties of dielectrics and ferroelectrics. New experimental methods using laser technique and permitting the study of induced and natural nonlinear properties of dielectrics are described. Stress is laid on measurements of laser beam induced optical birefringence and nonlinear light scattering processes, optical rectification, second and third harmonic generation of laser beams, mixing of light wave frequencies, and d.c. harmonic field induced second generation. Tables listing the available data on nonlinear optical polarizabilities of atoms and molecules and nonlinear optical susceptibilities of ferroelectric crystals are included. Particular attention is given to facts providing new insight into the statistical-molecular structure of dielectrics, the electron, ionic and domain structure of ferroelectrics, and phase transitions. Various uses of ferroelectric crys...

Polarized light source for underwater use

Abstract: A circularly polarized underwater light source comprising: a conventional unpolarized light source with a well-collimated output; an efficient optical polarizer, which employs multilayer interference polarization, total internal reflection, birefringent quarter-wave plates; and anti-reflection coatings; a lens to control the extent of the divergence of the illuminating beam; and an underwater housing with a dome-shaped window designed to withstand external hydrostatic pressures, part of the winding forming the lens.

Electrooptical properties of ferroelectric Gd2(MoO4)3

Abstract: On the basis of the symmetry of the free energy function describing properly the transition of gadolinium molybdate into the ferroelectric state, macroscopic relations are derived for the spontaneous birefringence and for the temperature dependence of the electrooptic coefficientsz ij . Since the transition parameters correspond to lattice vibrational modes with finitek, the resulting formulae differ considerably from those for classical ferroelectrics with transition parameterP. Experimental data are presented for the temperature dependence of freez 63 andz 41, clampedz 63 and free permittivity for a multidomain and single domain crystal. These results and earlier data on spontaneous birefringence compare well with theory.

Birefringence and Optical Rotatory Dispersion of a Compensated Cholesteric Liquid Crystal

Abstract: Utilizing deVries' model for the optical rotatory power of cholesteric mesophases, the temperature and wavelength dependence of the birefringence, Δn, of a compensated cholesteric liquid crystal was determined from optical rotatory dispersion measurements. Deviations from symmetry in the optical rotation around Tnematic of such a compensated system are due to the temperature dependence of Δn. Refractometer measurements of the ordinary refractive index were also performed and values of the three principal refractive indices were calculated. The ordinary refractive index of the focal conic texture was observed to be higher than that of the plane texture of the cholesteric phase.

Uses of Self‐Focusing and Dispersion Effects in Time‐Resolved Picosecond Spectroscopy

Abstract: Experiments with single picosecond pulses have shown certain interesting effects in the transmission of pulses through various Kerr‐active liquids, which prove useful in the study both of the laser pulses and of the liquid media. A technique is described for the accurate measurement of single‐pulse intensities using three‐photon fluorescence and the self‐focusing effect. Using this technique it is possible to derive values of the effective Kerr constant for picosecond pulses. It is observed that the duration of the induced birefringence is not governed solely by the Debye reorientation time but also by other faster (·10−13‐sec) mechanisms such as electron polarization or molecular ``rocking.'' The experimental results show that nitrobenzene and other molecules with relatively long Debye relaxation times have, under certain conditions, birefringence recovery times comparable to that of CS2. The experimental observations show that complete self‐focusing is experienced by only a small portion of a laser pulse.

Liquid crystal matrix display by electrically controlled birefringence

Abstract: The feasibility of a liquid crystal matrix display with a large number of independent points has been demonstrated using the electrically controlled birefringence (ECB) effect. A matrix with 50 × 50 points has been realized presenting colored, images.

Method of making a thin film wave guide employing stress induced birefringence by desposition in a polymer from solution

Abstract: A method for the fabrication of low loss birefringent polymer thin films on transparent substrates and their use for optical polarization wave converters are disclosed. The films consist of transparent acrylic or styrene polymers and copolymers and are deposited from liquid solution by evaporation of the solvent to provide substantial amounts of internal stress which induces the birefringence. The films are attractive because the birefringence and mean refractive index thereof are readily adjustable by annealing at a temperature below the softening point of the polymer and because they can be conveniently deposited on any of a large number and kind of substrate materials. The birefringence may also be adjusted by varying the solvent in the liquid solution. Furthermore, by properly selecting film thicknesses, the birefringence enables TE and TM polarization waves to propagate in the films degenerately. Such films may serve to simplify the construction and improve the operation of polarization wave converters, switches, modulators, filters and other thin-film devices requiring degenerate mode operation.

Use of Anisotropic Materials as Chemical Detectors

Abstract: The visual detection between crossed polarizers, of organic vapors on various liquid crystal films is reported. Non-selective detection is achieved in the ppm range. However, opportunities exist for bettering selectivity and sensitivity as illustrated with a combined polymer-liquid crystal detection system for amines. Also described is the detection of liquid droplets by utilizing changes in the birefringence of polycarbonate membrane filters.