Showing papers on "Birefringence published in 1969"

Piezo-Optical Birefringence Modulators: New Use for a Long-Known Effect

Abstract: A general description is given of a long-neglected use for the piezo-optic or photoelastic effect (stress-induced birefringence). An acoustic vibration, such as a fundamental extensional mode in a bar or long thin plate, is set up in a block of isotropic transparent material, such as glass or fused silica; the vibration is sustained by a transducer. The resulting modulated birefringence can be used in a variety of ways, notably to produce a beam of alternately left- and right-circularly polarized light for circular-dichroism measurements. Strains of the order 10−5 are required, considerably below the breakage point for most materials. Because advantage is taken of the high Q of the vibrational modes, typically 103 to 104, very small transducer power is needed, usually less than 1 W. The literally enormous useful angular aperture, of the order 50° total cone angle, makes the device far superior to Pockels or Kerr cells for many applications. Reference is made to current practical realizations and to present and future uses of the device.

An ultrafast light gate

Abstract: A simple technique is described for gating light on and off on the picosecond time scale. The gate is built in much the same fashion as traditional Kerr cells, the difference lying in the use of powerful optical pulses rather than electrical pulses to induce a birefringence in various liquids. The direct observation of the exponential decay (τ = 32 ± 6 psec) of the birefringence induced in nitrobenzene shows that orientational effects are largely responsible for the refractive index changes induced by light in this liquid.

Scarabaeid beetle exocuticle as an optical analogue of cholesteric liquid crystals

Abstract: Summary 1. A review is given of the optical and architectural analogies between cholesteric liquid crystals and certain insect cuticles (Coleoptera: Scarabaeidae). Earlier observations on the optical properties (reflexion of circularly polarized light and high form optical rotation) are confirmed and extended. Both cholesteric liquid crystals and lamellate cuticle have helicoidal structure (Fig. i). Even though their chemistry and physical states are very different, we are justified in making the analogy, since their optical properties depend primarily on the pitch of their helicoidal architecture. 2. The unusual optical properties were located for the first time in the outer 5 to 20 μ of the exocuticle. This layer is transparent and has regular spacings in the range required for interference colours according to Bragg's law. Among Scarabaeid beetles which show interference colours, we distinguish two types of outer exocuticle. (i) Optically active cuticles which reflect circularly polarized interference colours; show high angles of form optical rotation in transmitted light; and anomalous form birefringence perpendicular to the cuticle surface (reversible by deproteinization). (2) Optically inactive cuticles which show none of the above properties and in which the form birefringence is parallel to the cuticle surface. In the electron microscope the ultrastructure of these two types of outer exocuticle is clearly different. 3. All of the optically active species reflect left hand circularly polarized light, irrespective of the wavelength of the reflected colour. They therefore appear dark when viewed through a right hand circular analyser. The sense of reflected circularly polarized light does not reverse at higher wavelengths as recorded by previous workers. (A simple treatment is given for combinations of various wavelengths with retardation plates of varying values, as used in circular analysers.) We confirm earlier reports that the sense of reflected circularly polarized light is of the opposite sense to the transmitted light. 4. Using monochromatic light we have measured the anomalous dispersion with wavelength of the magnitude of optical rotation for various optically active cuticles. The dispersion curves change from negative values at lower wavelengths to positive values at higher wavelengths, and cross the zero optical rotation axis at a wavelength (AQ) corresponding to the interference colour of each sample. There is reasonable agreement between A0 and the interference colour calculated from ultrastructural evidence and by comparison with interference filters of known wavelength. A dispersion curve measured for a combined sample of two cuticles with different dispersion curves showed that the resultant is an algebraic summation of the two component curves. 5. We present the first experimental verification of existing mathematical treatments of anomalous form optical rotatory dispersion curves. Although these treatments were derived for cholesteric liquid crystals, they give a reasonable fit to our measured curves for cuticle. We have confirmed from our cuticle dispersion curves that a second zero value for optical rotation occurs at a wavelength higher than A0, as predicted by the theory of Chandrasekhar and Rao (1968). This has not yet been observed in any cholesteric liquid crystal system. 6. Our evidence shows that in optically active cuticle, interference colour is determined by helicoid pitch. In Lomaptera interference coloration follows the bilateral symmetry of the insect. Hence helicoidal pitch is controlled in a bilaterally symmetrical manner. However, the sense of helicoid rotation is the same all over the beetle and is therefore bilaterally asymmetrical. This supports the view that helicoid pitch is under the local control of the epidermal cells which secrete the cuticle, whereas its sense of rotation may be determined by an extracellular self-assembly process. In view of the self-assembling properties of cholesteric liquid crystals, it is tempting to suggest that helicoidal cuticle could be formed by the stabilization of a liquid crystal. 7. We discuss in detail the differences between optically active and inactive cuticles. The constructive interference colours arising from both types are then briefly compared with other multiple layer reflecting systems in other animals. 8. A detailed comparison is made between the optics of cuticle and cholesteric liquid crystals. The optical analogy provides a two-way contact between cuticle biophysicists and liquid crystal physical chemists.

Electromagnetic Propagation through Materials Possessing Both Faraday Rotation and Birefringence: Experiments with Ytterbium Orthoferrite

Abstract: Electromagnetic wave propagation through materials that possess both Faraday rotation and birefringence is analyzed A matrix equation is developed which relates the amplitude and relative phase of the electric vectors between any two points along the propagation direction It is shown that the presence of birefringence can drastically affect the behavior of wave propagation and that it is considerably different from pure Faraday rotation Methods of measuring the material parameters are also described Criteria for viewing domains in this type of material are established It is shown that the thickness of the sample plays a great role in determining the contrast between domains and at some thicknesses no contrast at all can be obtained It is also shown that the method using elliptical analyzers gives greater contrast over the plane analyzers Photographs of domain patterns in a wedge of ytterbium orthoferrite are presented and they verify the calculated results

Ferroelectric ceramic electrooptic materials and devices

Abstract: Thin polished plates of hot-pressed rhombohedral lead zirconate-lead titanate ceramics possess one of two types of electro-optic properties depending on the nominal grain diameter. In poled coarse-grained ceramics the electrooptic effect of importance for devices is the dependence of the light scattering properties on the orientation of the ceramic polar axis (electrical poling direction). The light scattering properties are essentially independent of the magnitude of electrical poling (ferroelectric remanence state). Poled fine-grained ceramics are birefringent, and their light transmission characteristics are similar to those of optically uniaxial crystals. These materials exhibit orthotropic symmetry with respect to the optic axis, which coincides with the ceramic polar axis. The fine-grained ceramic electrooptic effect of primary importance for devices is the dependence of the effective birefringence on the magnitude of electrical poling as well as on the intensity of the applied biasing electric field. Retardation of a ceramic plate can be varied incrementally by partial switching or continuously by application of a nonswitching bias field. Both coarse- and fine-grained ceramics have the property that localized areas as small as 25 µ by 25 µ can be poled or switched independently without affecting the light transmission characteristics of the surrounding area. The locally switched areas are stable with time, but they can be "erased" by switching them back to their original orientation. Each locally switched area can function as a light shutter, valve, or spectral filter depending on the ceramic material, the switching mode, and the characteristics of the incident light.

Kerr effect in methane and its four fluorinated derivatives

Abstract: Electric birefringence has been measured at a wavelength of 632.8 nm over a range of temperature and pressure in the gases CH4, CH3F, CH2F2, CHF3 and CF4. The results yield values of the second hyperpolarizability γ for CH4 and CF4 and, for CH3F, CH2F2 and CHF3, the first hyperpolarizability β and the difference (α33–α) between the optical polarizability component in the direction of the molecular dipole and its mean. For CH2F2(α33–α) is unusually small; the birefringence changes sign as the pressure is increased, the change occurring at 1.7 bar at 244°K. Limitations of a bond additivity model for β are exposed, and the importance of hyperpolarizability contributions to the Kerr constant demonstrated. The density dependence of the birefringence in the five gases is compared with the predictions of simple theoretical models, but agreement is in most cases poor.

Dispersion of the Refractive Indices and Birefringence of CdSxSe1−x Single Crystals

Abstract: The spectral dependence of the refractive indices and birefringence of CdSxSe1−x (including CdS and CdSe) single crystals has been investigated from the fundamental absorption edge up to the lattice vibration spectrum in the temperature interval 100 to 600 °K. In the region of v > 5000 cm−1 the measurements are carried out by the method of prism (with an absolute error for n of 5 × 10−4), for v < 5000 cm−1 by the modified interference method (with an absolute error for n of 5 × 10−3, and for Δn = ne − no of (2 to 4) × 10−5). The results are discussed. [Russian text Ignored]

An Introduction to Nonlinear Optics

Abstract: 1. Introduction.- 1.1. The Scope of Optics.- 1.2. Historical Background.- 1.3. Linearity in Optics.- 1.4. Nonlinearity in Other Fields.- 1.5. Nonlinearity in Optics.- 1.6. Scope of this Book.- 2. Background of Nonlinear Optics.- 2.1. Electromagnetic Theory of Light.- 2.2. Electromagnetic Theory of Linear, Isotropic Media.- 2.3. Modes.- 2.4. Geometrical Optics.- 2.5. Quantum Theory of Radiation Process.- 3. Properties of Optical Media.- 3.1. Introduction.- 3.2. Dispersion.- 3.3. Rayleigh Scattering.- 3.4. The Debye-Sears Effect.- 3.5. Birefringence.- 3.6. Zeeman and Stark Effects.- 3.7. Electrostriction and Piezoelectricity.- 3.8. Electrically Induced Birefringence.- 3.9. Optical Activity.- 3.10. Magnetooptical Effects.- 3.11. Fluorescence and the Raman Effect.- 3.12. Intensity-Dependent Optical Phenomena.- 4. Nonlinear Phenomena in Passive Media.- 4.1. Introduction.- 4.2. Electromagnetic Waves in a Nonlinear Dielectric: Method of Solution.- 4.3. The Role of Coherence in Harmonic Generation.- 4.4. The Nonlinear Susceptibility Tensor.- 4.5. Traveling-Wave Second-Harmonic Generation.- 4.6. Index Matching in Birefringent Materials.- 4.7. Boundary Conditions.- 4.8. A Numerical Example.- 4.9. Index Matching as Momentum Conservation.- 4.10. Harmonics Higher than the Second.- 4.11. Optical Rectification.- 4.12. Optical Mixing and Parametric Amplification.- 4.13. Self-Focusing of Optical Beams.- 5. Nonlinear Optical Phenomena in Active Media.- 5.1. Similarities and Contrasts.- 5.2. Raman Processes.- 5.3. Brillouin Scattering.- 5.4. Interactions of Light with Free Electrons.- 5.5. Optical Nonlinearity in Gases.- Appendix. Free and Forced Oscillations in Slightly Nonlinear Systems.

Infrared Detection by Optical Mixing

Abstract: A theoretical discussion is given of infrared detection systems employing an optically nonlinear crystal, a laser in the visible, and photomultiplier to detect the light produced at the sum or difference frequency. Three optical mixing systems are considered in detail and compared with direct detection: (a) cinnabar (HgS) in a single‐pass optical system with the He–Ne 0.6328 μm cw laser, (b) the same crystal and laser with a ring resonator and narrow‐band output filter, and (c) an ideal resonant system with a crystal as nonlinear as HgS but without absorption or double refraction. The noise output consisting of up‐converted thermal noise and (in the case of the difference frequency) optical parametric noise is computed quantitatively. These systems have too small a quantum efficiency to compete with a heterodyne system employing an ir laser and a detector of high quantum efficiency such as a Ge:Cu‐cooled photoconductor. The Ge:Cu detector has however a large dark noise compared to a good photomultiplier, and consequently optical mixing can surpass nonheterodyne direct detection if the required value of B≡(S/N)Δf is sufficiently small. The range of superiority of optical mixing over nonheterodyne direct detection extends high enough in B for Morse code for system (a) (if sum frequency is used), nearly high enough for a telephone channel for (b) and up to the television level for (c).

Elastic Wave Propagations and Acoustical Birefringence in Stressed Crystals

Abstract: The elastic wave propagations in deformed crystals with any symmetry are investigated theoretically. The rotationless acoustical tensor, which specifies the propagation condition, consists of the tensor based on the natural unstressed state and the perturbation term being proportional to the stress. The perturbation theory is applied to nondegenerate and degenerate cases with respect to the quasitransverse wave velocities. The perturbed wave velocities and the polarization directions are formulated by the stress suppressed on the crystals, and then the general formulas for the acoustical birefringence depending on the second‐ and third‐order elastic constants are reduced. The difference of the quasitransverse wave velocities is expressed by the sum of two terms: the difference of these in unstressed crystals due to the intrinsic anisotropy and the perturbation term due to the stress. In the cases of the cubic system and of the isotropic material, the explicit relations are calculated. For the isotropic material, the so‐called stress‐acoustical law holds.

Anomalous Dispersion of Birefringence of Sapphire and Magnesium Fluoride in the Vacuum Ultraviolet

Abstract: Previous measurements of the birefringence of sapphire and magnesium fluoride have been extended to their respective limits of transparency, revealing anomalous dispersion effects at short wavelengths, which are qualitatively discussed. Possible practical applications to Lyot filters and quarter-wave plates for Lyman-alpha are indicated.

Optical activity in a non-enantiomorphous crystal of class \overline{4}: CdGa2S4

Abstract: Optical activity has been observed for the first time in a crystal of the non-enantiomorphous class \bar 4 CdGa2S4 is optically isotropic at 4872 A (20°C) and this allows observation of optical rotation for propagation in directions away from the c axis. The magnitude of the optical rotatory power is 17.3 deg.mm−1 along (100) and 11.6 deg.mm−1 along (110). The form of the optical rotatory power for general directions in the (001) plane has the predicted symmetry, showing positive and negative lobes. The refractive indices and birefringence are temperature-dependent and the point of isotropy shifts from 4825 A at 0°C to 5780 A at 400°C.

Theory of Birefringence of Nematic Liquid Crystals

Abstract: A theory of the birefringence of nematic liquid crystals is de- veloped taking into account the intermolecular potential energy arising from dipole-dipole, anisotropic dispersion, induction and repulsion inter- actions. The potential energy exhibits a dependence on molecular orientation and is expressible ae - (uo + u1 cost9 + uz cosat9 + u4 cos48 + u6 cosee + ...) where t9 is the angle which the long axis of the molecule makes with the uniaxial direction of the liquid crystal. The birefringence of the medium is evaluated in terms of the Boltzmann distribution of the oriented mole- cules. The theory explains the experimentally observed result that the temperature coefficient of the extraordumy index is large and negative whereas that of the ordinary index is small and positive. Analysis of the data on p-azoxyanisole and p-azoxyphenetole shows that dispersion and repulsion forces play a predominant role in determining the temperahre variation of the birefringence. Assuming that the molecular librations in the liquid crystal can be represented by a system of harmonic oscillators, the rn librational mnpli- tude is evaluated for p-azoxyaniaole from recent measurements of the ultrasonic velocity. The increase in the rn amplitude With temperature in the nematic range is found to be in good agreement with that obtained directly from the experimental data on birefringence.

An ultrafast light gate

Abstract: A device has been built which is capable of gating light on and off on the picosecond time scale. The gate is built in much the same fashion as traditional Kerr cells, the difference lying in the use of powerful optical pulses rather than electrical pulses to induce a birefringence in various liquids. In the experiment, powerful light pulses from a mode-locked Nd:glass laser, ∼5 psec in duration (wavelength 1.06µ), are used to induce a birefringence in a number of liquids including CSµ, nitrobenzene, chlorobenzene, dichloroethane and others. The transmission of the gate as a function of time is probed by means of 0.53µ green light pulses derived from the 1.06µ pulses by second harmonic generation. With CS 2 the transmission curve has a width of 8 psec; the peak transmission is 10% and the extinction ratio is 200. With nitrobenzene the curve has an exponentially falling tail on one side. The associated decay time is 32± 6 psec. Since 32 psec is a time characteristic of molecular reorientation times, this observation provides direct support for the long held belief that orientational effects dominate light induced refractive index changes in nitrobenzene.

Ferroelectric ceramic materials

Abstract: An electrooptic ferroelectric ceramic material of a lead lanthanum zirconate titanate solid solution having about 5 to 25 atom percent lanthanum with the ratio of zirconium to titanium varying from about 5/95 to about 95/5, hot-pressed, having an optical transmittance throughout the visible spectrum of about 100 percent for optically polished plates about 0.25 millimeters thick, with an effective birefringence of from about -0.003 to 0.03 at saturation remanence polarization to near zero as the remanent polarization is switched to electrical zero, and an effective electrooptic coefficient at saturation remanence from about 1 X 10 2 to 5 X 10 2 m2/C, and for memory applications a coercive field from about 2 to 10kV/cm.

Adjustable bandwidth optical filter

Abstract: THE OPTICAL APPARATUS USED IN A TELEVISION SYSTEM, FOR EXAMPLE, INCLUDES A SERIES ARRANGEMENT OF THREE BIREFRINGENT ELEMENTS OF DIFFERENT THICKNESS INTERSPERSED WITH TWO QUARTER WAVE DELAY ELEMENTS TO CONSTITUTE AN OPTICAL FILTER. THE FILTER IS PLACED IN THE LIGHT PATH BETWEEN AN OBJECT AND THE IMAGE FORMED AT THE PHOTOSENSITIVE ELEMENT OF A CAMERA TUBE. THE SPATIAL FREQUENCY BANDWIDTH OF THE LIGHT PASSING THROUGH THE FILTER IS CONTROLLABLE IN ONE OR MORE DIRECTIONS AND IN THE SAME OR DIFFERENT AMOUNTS IN A PLURALITY OF DIFFERENT DIRECTIONS BY SUITABLE DIMENSIONING OF THE BIREFRINGENT ELEMENTS AND/OR BY APPROPRIATE ROTATIONAL POSITIONING OF THE ENTIRE FILTER ABOUT THE OPTICAL AXIS.

Apparatus for the measurement of flow birefringence of polymer melts at high shear stresses

Abstract: A description is given of a rectangular slit apparatus suitable for the measurement of streaming birefringence in molten polymers at much higher shear stresses than are currently available. Some results are given of measurements on a polystyrene and two polyethylenes up to and including the incipient point of melt fracture in circular capillaries. Measurements of the refractive index differences (n 11–n 33) were found in the lower shear stress region to lie close to (n 11–n 22) values measured with a coneand-plate apparatus

Laser mode selection and stabilization apparatus employing a birefringement etalon

Abstract: There is disclosed a stabilized single-frequency arrangement for a broadband laser, such as a neodymium ion laser, in which a resonant etalon including birefringent material is disposed in the resonator in the path of the radiation and is tilted to select only one axial mode of oscillation in each of two orthogonal polarizations. In one specific embodiment, the resonator is tuned for maximum intensity of the mode of one polarization in response to a nearly linear intensity-frequency discriminant derived from the mode of the other polarization, which is provided with an operating point on a side of a transmission curve of the etalon.

Role of surface dipoles on axon membrane.

Abstract: A physical model of nerve excitation and conduction is proposed based on the discovery of three new axon membrane properties: the negative fixed surface charge, the birefringence change, and the infrared emission.

Liquid crystal display element

Abstract: An electro-optical display device employing a cell comprising a nematic liquid between two glass plates whose inner surfaces have been coated with transparent electrodes. Such coated electrodes are rubbed with a cloth or filter paper so that the liquid crystal film becomes oriented along the direction of rubbing. Such film will be homogeneous and strongly birefringent so that when an electric field is applied to the electrodes of the cell and the latter is viewed between crossed polarizers, a marked contrast in light between the quiescent and active states, respectively, of the cell is observed, even in the presence of ambient illumination of the cell.

Study of the duration and birefringence of self-trapped filaments in CS 2

Abstract: Small-scale optically trapped filaments in liquid CS 2 were studied by side illumination and crossed polarizers using the second-harmonic radiation of a mode-locked Nd3+: glass laser. Filaments produced by Nd3+laser radiation (1.06 μ) exhibited birefringence of magnitude (2 \pm 1) \times 10^{-3} and duration times second.

Laser recording system using photomagnetically magnetizable storage medium

Abstract: An optical coherent light data recording and reading system utilizing an erasable and/or permanent recording medium The recording medium is formed of a layer of substantially transparent photomagnetically responsive magnetizable material having a anisotropic optical response under magnetization coated on a substrate or carrier The substrate may have a reflective surface or a thin reflective metal layer may be interposed between the substrate and the layer of magnetizable material A polarized beam of coherent light generated by a laser in a wavelength suitable for optical pumping of exchange resonance spinwave modes of the magnetizable material is focused by an optical recording head onto the photomagnetically responsive layer of magnetizable material in a diffraction limited spot size Optical pumping is achieved by either parametric excitation or quantum-mechanical excitation The laser beam and recording medium are translated relative to each other and the rate of translation and laser intensity are adjusted so that the thermal temperature developed in the layer of magnetizable material is less than the Curie temperature of the material during recording The recording laser beam is optically modulated to induce localized photomagnetization along the recording medium to thereby provide remanent tracks of variable birefringence in the magnetizable material as a function of a signal to be recorded Readout is accomplished with a reading laser by means of the Faraday effect Preferably optical recording takes place in the spectral region of maximum absorption efficiency by the exchange resonance modes of the recording material while optical readout takes place in the spectral region of maximum Faraday rotation Ramanent data tracks are erased by secondary scanning of the recording laser at an intensity and/or scanning rate sufficient to heat the record material above the Curie temperature

Effect of birefringence on low-angle light-scattering patterns from oriented polymer films. II

Abstract: : The effect of birefringence of a polymer film upon its photographic light scattering pattern is considered for the case of a single anisotropic two-dimensional spherulite imbedded in a birefringent matrix. It is shown that for the case of a polarizer and analyzer crossed at +45 deg. and -45 deg. to the analyzer the scattering pattern is modified in a manner agreeing with experimental observation. (Author)