Showing papers on "Birefringence published in 1973"

Optical Constants of Far Infrared Materials. 2: Crystalline Solids

Abstract: The far infrared optical constants of four crystalline materials at room temperature and at 1.5 K are reported. The materials are crystal quartz, sapphire, germanium, and silicon. The first two of these are birefringent (uniaxial) and both sets of optical constants are reported. The measurements extend over the range from 30 cm−1 to 350 cm−1.

Optical Kerr effect in glass waveguide

Abstract: We have observed light induced birefringence in glass optical waveguide. This effect can be observed at low powers in waveguide because of the high power densities which are maintained over long lengths of guide. This effect is potentially useful as a wide‐band pulse modulator or as a device for switching or measuring the length of picosecond pulses.

Transient behavior of the electrically controlled birefringence in a nematic liquid crystal

Abstract: An homeotropic cell is built with a thin layer (5–25 μm) of nematic liquid crystal such as MBBA sandwiched between two indium oxide coated glass plates. The transient behavior of the cooperative angular variation of molecules submitted to an electric field step is studied theoretically. Experimental results are obtained by optical detection of the birefringence variations in the cell. Comparison of these studies allows one to determine the viscosity coefficient γ1(−λ1 in Leslie's notation).

Birefringent liquid crystal structure

Abstract: A field-effect liquid crystal structure having birefringent properties controlled by crossed electric fields in conjunction with crossed polarizing units.

New multicolor liquid crystal displays that use a twisted nematic electro‐optical cell

Abstract: Two new variable color display device arrangements are described. These arrangements combine the unique polarization switching capabilities of the twisted nematic liquid crystal electro‐optical cell with the anisotropic optical properties of separate passive optical elements. In one scheme, the passive element is a birefringent film in combination with a neutral polarizer, and colors are transmitted by the selective interference of white light. In another design, where the passive element is a pleochroic filter, the transmitted colors result from the selective absorption of white light. These arrangements make possible large area displays, since the colors transmitted do not depend on the temperature or thickness of the nematic layer. Transmission curves and other color information are given for a number of examples.

Circular dichroism and rotatory dispersion near absorption bands of cholesteric liquid crystals

Abstract: A macroscopic theory is developed to explain the intense and highly structured circular dichroism (CD) and optical rotary dispersion (ORD) measurements of cholesteric liquid crystals in spectral regions of absorption, e.g., in the infrared. Oseen’s helical model of the dielectric tensor of the liquid crystal is used. The effects of each absorption band are represented by frequency-dependent, complex terms in the dielectric tensor. Assuming reasonable values for the absorptive parameters of the band, we are able to explain the magnitude and shape of the CD and ORD spectra, as well as their trends with the pitch of the helix. The calculated sign of the Cotton effect is shown to depend upon the direction of polarization of the absorption band with respect to the background birefringence. The observed preponderance of bands with one sign is qualitatively explained on the basis of the molecular structure of the liquid crystal.

Polarization field and molecular order in smectic liquid crystals.

Abstract: In the smectic A and B mesophases, the polarization field is anisotropic and the extraordinary and ordinary refractive indices n e and n o are related to the effective polarizabilities αe and αo and the internal field constants γe and γo by the Neugebauer's relations. The Neugebauer relations lead to the Born relation which is valid to a high degree of accuracy particularly for the long wavelengths. The paper presents a method for calculating the anisotropic internal field constants and the ratio of αe to αo, even if density data are not available. The birefringence data reported by Pelzl and Sackmann for six cinnamates which exhibit both smectic A and B mesophases are discussed in terms of the theory and results are presented with regard to the internal field constants and the ratio of αe to αo at different temperatures. Their variations are explained as due to mainly the rotational isomerism exhibited by the alkyl and alkoxy endgroups in the different compounds.

Transverse field effects in nematic liquid crystals

Abstract: A novel electro‐optic effect has been observed in thin homeotropic nematic layers. Electrodes, such as a pair of parallel lines, are located on a planar surface in contact with the liquid. Deformation of the homeotropic ordering occurs when the applied field exceeds a threshold strength. Induced optical birefringence and diffraction have been observed, and electrically controlled optical transmission and reflection have been attained. Experimental data are given for a cyano‐aniline mixture with e∥ − e⊥ > 0 and for negative‐anisotropy materials.

Structural dependence of birefringence in the chalcopyrite structure. Refinement of the structural parameters of ZnGeP2 and ZnSiAs2

Abstract: We have found that, as a consequence of the experimentally observed geometrical regularity of the BC4 tetrahedra in AIIBIVC2V crystals with the chalcopyrite structure, the birefringence of the crystals depends on the anisotropic polarizability of the A–C bonds only. This has allowed us to predict the birefringence of several AIIBIVC2V crystals for which reliable experimentally determined values are not available. To provide additional crystal structure data, as required for the predictions, we have refined the structural parameters of ZnGeP2 and ZnSiAs2 by the method of least squares with counter measured single crystal x‐ray diffraction data; the positional parameters (estimated standard errors in parentheses) are xP=0.25816 (0.00044) and xAs=0.26575 (0.00012). Final values of the conventional agreement index R were 0.029 and 0.022 for ZnGeP2 and ZnSiAs2, respectively. The GeP4 and SiAs4 tetrahedra are regular within experimental error. Experimentally determined bond distances are: Zn–P, 2.375 (0.002) ...

Anomalous electro‐optic properties of ferroelectric strontium barium niobate and their device applications

Abstract: A longitudinal electro‐optic memory effect is observed in ferroelectric single‐crystal SrxBa1−xNb2O6 with tetragonal symmetry. The changeable birefringence depends on the remanent polarization of the crystal and can be switched by voltage pulses. These optical characteristics, which seem to be similar to the optical properties observed in ferroelectric Pb3MgNb2O9 with a diffuse phase transition, can be utilized in light‐valve devices which operate in the longitudinal mode without a transverse electric field or strain bias.

Theory of second-harmonic generation in optical waveguides

Abstract: A theory for the initial rate of second-harmonic generation (SHG) in planar optical waveguides for phase-matched and nonphase-matched cases is derived. The derivation is carried out both by a ray treatment and by a wave treatment and the results of the two are compared. Although formally and from the point of view of physical interpretation the two treatments look very different, the final results are the same if allowance is made for the Goos-Haenchen shift. Dependences of the amplitude of the second harmonic on the amplitude of the fundamental A ω and on distance are quite similar to those for bulk SHG even though the phase-matching condition is quite different. Determining the characteristics of some of the phase-matched modes, we find that, for the same A ω , it is possible to obtain a generation rate in waveguide comparable to that in the bulk. The highest generation rate is achieved, as expected, with both fundamental and harmonic having mode number 0. Phase matching can be achieved in this case without birefringence and with all three media having normal dispersion. The decrease in generation rate in going to mode pairs other than 0,0 is less than a factor 2 in some cases.

A ray-optical analysis of thin-film polarization converters

Abstract: A compact formula is given for the Goos-Haenchen shifts occurring for total internal reflection of light from anisotropic media. This is used in a coupled-wave analysis of polarization conversion in thin-film waveguides deposited on optically birefringent substrates. A numerical example illustrates the considerable influence of the Goos-Haenchen shifts on the conversion length.

Electric birefringence of poly-L-lysine hydrobromide in methanol–water mixtures and helix–coil transition induced by high electric fields

Abstract: The electric birefringence of poly-L-lysine hydrobromide in methanol–water mixtures has been measured at 25 °C over a wide range of field strengths by use of the rectangular pulse technique. An abrupt change in the specific Kerr constant was observed between 87 and 90 vol % methanol, corresponding to the solvent-induced helix–coil transition. The specific Kerr constant increased rapidly with dilution in the random coil form, and more slowly in the helical conformation. The field strength dependence of the bire fringence at various concentrations, for both the helical and coil conformations, can be described by a common orientation function, which resembles the theoretical one for the case of permanent dipole moment orientation. This is interpreted in terms of the saturation of ion–atmosphere polarization. The optical anisotropy for the helical conformation was much larger than that for the coil form. Anomalous birefringence signals were observed above a critical field strength (about 5 kV/cm) in 90 vol % methanol. The birefringence passed through a maximum and began to decrease slowly before the pulse terminated, reaching a steady-state value. This steady-state value was closer to that of the coil in the coil in the limit of very high fields. The results indicate that a transition from the charged helix to the charged coil is induced by high electric fields in the transition region. This effect can be explained on the basis of the polarization mechanism proposed by Neumann and Katchalasky.

Automatic birefringence measuring apparatus

Abstract: Birefringence resulting from the relative retardation of light waves propagating at different speeds through a stressed plate or coating is measured automatically by splitting a light wave emerging from the stressed plate or coating into at least two beams, filtering each beam with a filter which transmits a different wave length, transforming the light intensity from each filter into electrical signals and using the electrical signals to measure the resulting phase shift which is directly proportional to the birefringence.

Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as-spun polyolefin fibers

Abstract: Three different polyolefins, a linear polyethylene, an isotactic polypropylene, and an isotactic polybutene-1, were melt-spun into filaments. The degree of orientation of the filaments was measured by polarized-light microscopy, x-ray diffraction, and a retraction technique, and the results were then related to the melt-draw ratio. The increase in the elastic deformation ratio of polymer chains by spin-stretching, estimated by thermal retraction at a temperature above Tm, was monotonic with respect to the melt-draw ratio. On the other hand, as-spun filaments of polyethylene and polypropylene were characterized by a plateau in birefringence over the range of melt-draw ratios from 8 to 80. The change in orientation functions for crystals in these filaments was similar to the change of birefringence. On the other hand, the birefringence and the crystalline orientation functions for polybutene-1 increased smoothly with increasing melt-draw ratio. The most highly melt-drawn filaments of these polymers had a strongly oriented structure, corresponding to that in highly cold-drawn specimens.

Line defects in barium titanate observed by polarized light microscopy

Abstract: Line defects lying parallel to the tetragonal c axis within ferroelectric a domains of barium titanate have been observed using polarized light. When the domain wall is inclined to the light beam, the-wall may exhibit thickness fringes, and the defects, which lie normal to the light beam, have oscillatory contrast of the same periodicity. A theoretical analysis of stress birefringence contrast due to dislocations in an anisotropic material shows that the contrast is consistent with the defects being screw dislocations. Analysis of the contrast of the defects in X-ray topographs confirms this conclusion. The stress birefringence analysis shows that, as a result of the optical anisotropy of the unstrained crystal, the contrast of a dislocation viewed from the side is much higher than in an isotropic material. The behaviour of the normal modes of propagation in the vicinity of a dislocation is compared with the behaviour of Bloch waves in electron or X-ray diffraction.

Electrical birefringence apparatus for conducting solutions.

Abstract: Birefringence studies on conducting solutions are not easily performed for several experimental reasons; these difficulties are discussed. An apparatus which allows Kerr effect experiments on high ionic strength solutions is described. It is built around a fast high‐power switching device, which generates the electric pulse. Rectangular pulses of 30 kV can be applied to weakly conducting solutions (<10−2M NaCl). For a 0.1 M NaCl solution, the amplitude still reaches 15 kV. In any case, the 10%–90% rise and decay time is about 50 nsec. The pulse amplitude and duration are adjustable in large limits. This pulse generator can also be used to apply reversing pulses or sinusoidal wave bursts. It is possible with this apparatus to measure the electric birefringence of urea, for instance, in high ionic strength solvents (NaCl 0.1 M).

Study of Self-Focusing and Self-Phase-Modulation in the Picosecond-Time Regime

Abstract: Study of the propagation of a single picosecond pulse of a mode-locked Nd-glass laser in CS2 nitrobenzene and toluene by observations of the birefringence and spectral changes in self-focused laser light. Multiple second-harmonic probing beams are used for birefringence measurements in a single IR pulse in various portions of the active cell. The orientational Kerr effect is found to be the prime factor of induced birefringence in nitrobenzene and toluene. The results for CS2 are also consistent with this mechanism and show that the duration of an IR pulse in the focal volume is less than that of the incident pulse. The properties of beams which are focused within the cell by an external lens are also investigated.

Birefringent Branching Filters for Wideband Optical FDM Communications.

Abstract: Optical branching filters consisting of birefringent filters for combining and splitting eight optical channels are studied in detail both theoretically and experimentally. Multisegment structures were used in the channel-splitting filter to suppress the crosstalk from other channels. The crosstalk of −15.5 dB was realized for a signal bandwidth Bin equal to 67.5% of the channel separation. Discussions on the pulse response of the filter system, effects of nonzero extinction ratio, and influences of the filter frequency detuning are included.

Nonlinear optical crystals and their applications

Abstract: Describes the phenomena fundamental to efficient optical frequency mixing of laser beams in transparent, acentric birefringent crystals, with particular emphasis on phase-matching, effective nonlinear coefficients and results for focused beams. Methods for measuring nonlinear coefficients, for predicting them by semi-empirical rules and for seeking improved crystals are reviewed. The properties of crystals known at this time to be useful for efficient phase-matched optical frequency mixing are tabulated; features important for the growth and preparation of samples with high optical quality are discussed. Recent achievements in applying the crystals are reviewed in sections on optical second-harmonic generation of laser light, optical parametric oscillators as tunable laser-like sources, infrared signal and image upconverters and difference-frequency generators. Applications to other technologies (piezoelectricity, pyroelectricity, electro-optic modulation) are briefly mentioned. Prospects of developing improved crystals or of using existing crystals in more sophisticated ways are assessed.

Stress birefringence in ferrimagnetic garnets

Abstract: We have measured the stress birefringence in several magnetic garnets (YIG, YbIG, GdTbIG, and CVBIG) and one nonmagnetic garnet (GdGaG). Measurements were made at room temperature by applying both a static uniaxial stress and a saturating magnetic field along 〈100〉 and 〈111〉 axes. Nonuniformities in the samples and the loading procedure made it valuable to measure the birefringence automatically as a small light spot scanned the crystal. It was found that the photoelastic effect is 2 orders of magnitude too small to account for the linear magnetic birefringence as a birefringence associated with the macroscopic magnetostrictive strain. The stress optical constant B (Δn/stress) in the magnetic crystals was found to be about −1.8×10−13 cm2/dyn for stress along 〈100〉, and −3.0×10−13 for stress along 〈111〉. Diamagnetic GdGaG has values for B of −1.2×10−13 and −3.0×10−13, respectively. It seems plausible then that the tensors describing the photoelastic and magneto‐optic effects are not strongly coupled. The d...

Improved tuning apparatus for a dye laser

Abstract: One or more birefringent plates are placed within the optical cavity of a dye laser Each of the plates is positioned at an angle, such as Brewster''s angle with respect to the light reflected within the optical cavity of the dye laser The output wavelength from the dye laser is tuned by rotating the birefringent plates while maintaining the plates at the same angle

Stability of the PBLG Helix at High Temperature and the Wormlike Character of the Helix

Abstract: Viscosity and electric birefringence of poly(γ-benzyl-L-glutamate) (PBLG) in m-cresol have been measured up to 200°C (viscosity) and up to 170°C (electric birefringence), respectively. Dipole moments, optical anisotropy factors, mean relaxation times of birefringence, and intrinsic viscosities of PBLG at various temperatures have been determined. No abrupt changes which suggest breakage of the helix structure have been observed on hydrodynamical and electrooptical properties. However, the PBLG helix becomes considerably more flexible with increasing temperature. Persistence lengths of PBLG helix at various temperatures have been estimated from dipole moments, relaxation times, and intrinsic viscosity data.

Study of the wavelength dependence of optically induced birefringence change in undoped LiNbO3

Abstract: Optically induced birefringence change (``optical damage'') has been studied in undoped LiNbO3 from 400 to 800 nm by using an incoherent light source. Optical damage was observed over the entire wavelength range, with damage peaking near 415 nm. Structure, which could not be observed by normal optical absorption measurements, was seen in at least three regions of the damage‐wavelength curve.

Liquid crystal electric field sensing measurement and display device

Abstract: A flat panel, electric field controlled device is provided for the measurement and display of electrical parameters such as voltage, the voltage sensing effect being provided by a nematic liquid crystal medium having high positive dielectric anisotropy and placed in a thin flat-sided optically transparent cell. Optical transmission of the nematic liquid crystal medium is controlled by voltages applied to interdigital arrays of parallel electrode elements affixed on the inner surface of only one of the transparent parallel cell walls. Continuous relative changes in the respective potentials applied to the electrode arrays provide continuous analog movement of the borders between birefringent and non-birefringent areas formed in the liquid crystal medium.