Optical Anomalies Research Articles

On the origin of inhomogeneity of anomalous birefringence in mixed crystals: an example of alums

Optical anomalies (deviations of the symmetry of optical properties from the ideal symmetry of the crystal) occur in many minerals and synthetic compounds and have been under investigation since the last century. An important feature of optically anomalous mixed crystals is a high degree of optical inhomogeneity, whereas the optical patterns of mixed crystals without anomalies are usually rather uniform. This work is devoted to the study of this phenomenon. As a model object we have chosen mixed alum crystals, which were known for their anomalous birefringence and which revealed the following types of optical inhomogeneities: (1) sector zoning; (2) concentric zoning; (3) subsector zoning; (4) stripes normal to growth front. The inhomogeneity of anomalous birefringence of mixed crystals of alums can be explained by superposition of several effects: mismatch strain, strain along dislocations and growth ordering of isomorphous components. Optical inhomogeneities due to the sector zoning of crystals and their dislocation structure arise even under stationary growth conditions and stationary micromorphology of the growing face. Both variable growth conditions and the relief of the growing face strongly intensify the optical inhomogeneity due to three interrelated factors: (1) a significantly inhomogeneous mismatch strain; (2) a variable degree of ordering of isomorphous components due to the compositional inhomogeneities; (3) different degrees of ordering of isomorphous atoms caused by different orientations, heights and velocities of growth steps. These effects lead to the formation of subsector zoning and zoning superimposed on the optical sector zoning. These optical structures are crossed by birefringent stripes arising from dislocations.

Electrodynamics of nearly ferroelectric superconductors

We report here the frequency-dependent optical response of a nearly ferroelectric superconductor (NFE-SC), like Na$_{x}$WO$_3$, or n-SrTiO$_3$. From $\omega =0$, up to a critical frequency $ \omega_{c1}$, Meissner-like field extinction occurs as in a usual superconductor. In the "anomalous" region $\omega_{c1}<\omega<\omega_{TO}$ (the TO frequency of the NFE) the field propagates as in a dielectric. For $\omega >\omega_{TO}$ Meissner damping recurrs, then at higher $\omega$, dielectriclike propagation is found. New optical anomalies (peaks in transmission) are predicted for a film of NFE-SC below the soft mode frequency $\omega_{TO}$. These effects are due to including the contribution of the NFE displacement current in the solution of the coupled Maxwell, lattice and London equations. Quantitative calculations are given for the NFE-SC n-SrTiO$_3 $ to illustrate this.

On the origin of anomalous birefringence in grandite garnets

AbstractThe origin of anomalous birefringence of grossular–andradite (grandite) garnets from skarns in Mali and Russia was considered. The crystals had complex superposition of two phenomena: mismatch compositional strain (stress birefringence) and growth ordering of atoms (growth dissymmetrization). Study of the crystals using several experimental techniques (optical microscopy, microprobe analysis, X-ray diffraction topography and X-ray single crystal diffraction) as well as calculations of anomalous birefringence has confirmed this hypothesis. Depending on the crystal composition and growth conditions, the relative magnitude of each phenomenon controls the various optical effects. As a result one can see two groups of crystals which are found to have fundamentally different anomalous optical properties: crystals with low (&lt;0.001) and high (0.001–0.015) values of birefringence. The spatial distribution of birefringence within each group is different and this fact is related to different mechanisms causing optical anomalies: stress birefringence and growth dissymmetrization for these two groups, respectively.

Magnetostructural effects and phase transition inCr2O3under pressure

We have successfully calculated the electronic and structural properties of chromia (Cr_2O_3) in the Local Spin Density Approximation (LSDA). We predict a transformation from the corundum to the Rh_2O_3(II) structure around 15 GPa in the anti-ferromagnetic (AFM) phase as well as in the paramagnetic (PM) insulating state which occurs above the Neel temperature (T_N). This transition is relevant to interpreting the optical anomalies observed in the absorption spectrum of ruby under pressure. We have modeled the structural properties of the PM state using a Landau-like expansion of the magnetostriction energy. This treatment correctly describes the structural anomalies across T_N in the corundum phase and indicates that the AFM and PM insulating states should have distinct compressive behaviors.

Effect of growth conditions on the birefringence of mixed crystals revealed in alum solid solutions

AbstractAn experimental study of optical anomalies in solid solutions of alums in relation to their composition, growth temperatures and rates, and hydrodynamic regime was carried out. Theoretical analysis of the data showed that they can be understood in terms of a mechanism of kinetic ordering of the isomorphous atoms (the phenomenon of so-called ‘growth dissymmetrization’). A theoretical model is presented which is supported by data for a number of minerals and synthetic compounds, which are known for their optical anomalies due to growth dissymmetrization.

Prevalence and origin of birefringence in 48 garnets from the pyrope-almandine-grossularite-spessartine quaternary

Other| December 01, 1998 Prevalence and origin of birefringence in 48 garnets from the pyrope-almandine-grossularite-spessartine quaternary Anne M. Hofmeister; Anne M. Hofmeister Washington University, Department of Earth and Planetary Sciences, Saint Louis, MO, United States Search for other works by this author on: GSW Google Scholar Rand B. Schaal; Rand B. Schaal Search for other works by this author on: GSW Google Scholar Karla R. Campbell; Karla R. Campbell Search for other works by this author on: GSW Google Scholar Sandra L. Berry; Sandra L. Berry Search for other works by this author on: GSW Google Scholar Timothy J. Fagan Timothy J. Fagan Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (11-12_Part_1): 1293–1301. https://doi.org/10.2138/am-1998-11-1218 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Anne M. Hofmeister, Rand B. Schaal, Karla R. Campbell, Sandra L. Berry, Timothy J. Fagan; Prevalence and origin of birefringence in 48 garnets from the pyrope-almandine-grossularite-spessartine quaternary. American Mineralogist 1998;; 83 (11-12_Part_1): 1293–1301. doi: https://doi.org/10.2138/am-1998-11-1218 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Forty garnets are anisotropic among 48 in a suite spanning the quaternary system Mg 3 Al 2 Si 3 O 12 - Fe 3 Al 2 Si 3 O 12 - Ca 3 Al 2 Si 3 O 12 -Mn 3 Al 2 Si 3 O 12 (Py-Al-Gr-Sp). The eight isotropic specimens are too thin (>0.4 mm) for detection of weak anisotropy. Birefringence (delta ) in the remaining 40 garnets is low (delta = 0.0001 to 0.0006) and undulatory in appearance, suggesting that most optical anomalies in quaternary garnets, including the pyrope-almandine-spessartine ternary, originate through residual strain. Multiple or alternate origins are not precluded for the few samples with nearly uniform retardation or unusual sector twinning. An inverse correlation exists between degree of birefringence and stresses encountered during tectonic deformation. That is, mantle garnets from kimberlites (e.g., Py 37 Al 36 Gr 27 ) have the highest delta values. As geologic setting is difficult to separate from composition, the inverse trend suggests that birefringence arises partially from internal factors. We propose that the mismatch in size between Ca (super 2+) and Mg (super 2+) exacerbates retention of residual strain. Short-range ordering is not entirely ruled out, but clustering has only been inferred for synthetics in the middle of the Py-Gr binary, a composition range unknown for natural samples, and domains are precluded in the natural samples by the recent X-ray studies of samples from similar localities. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Some peculiarities in the incommensurate phase transition in quartz

Optical anomalies near the phase transition temperature (Tc ) from the incommensurate (IC) to the α-phase were studied. In particular, large depolarization for a light propagating along the z-axis was found near Tc . The maximum of the birefringence (2·2 × 10−5) were observed in the so-called fog-zone where the ‘opalescence’appears. This and the related optical anomalies are due to the ferroelastic strains and domains induced by the modulation. However, the magnitude of the observed birefringence is by far larger than that expected from the currently accepted model unless the IC modulation wavevector k is much larger than that observed in the diffraction experiments. The results suggest the necessity of a new model for the IC phase transition in quartz.

Origin of optical anomalies in the ferroelectric phase transition region of SbSI and SbSBr crystals

The dependence of the full electronic potential V(z) in paraelectric and ferroelectric phases of SbSI and SbSBr crystals upon the normal coordinate of symmetry B 1u formed of atom displacements along the c(z) axis is studied in the vicinity of Sb atoms. The exponential dependence of the absorption coefficient K(E) upon the photon energy E is shown to be caused by interaction of electrons with the phonons of the normal mode B 2 1u.Thermal fluctuations of atoms in the xy plane induce fluctuations of anharmonicity of V(z) in the phase transition region around temperature Tc in SbSI and SbSBr. These anharmonicity fluctuations, in their turn, cause anomalies in the temperature dependence of the absorption edge In K(E) slope. It is demonstrated using the pseudopotential approach that the variation of the direct band gap during the phase transition is mainly determined by variation of the structure form factor when Sb atoms change their equilibrium position.

Theory of a fixed scatterer embedded in a turbid medium

Diffuse photon density waves are currently used to probe turbid media for optical anomalies such as tumors in tissue. A basic theory is established for detection of a fixed scatterer embedded in a turbid medium, including the effects of the medium’s boundaries. Several diffuse expressions are obtained for a scattered wave both reflected and transmitted through a turbid layer, as well as within the layer, including important cases of vertically incident light and vertical observation by optical fibers. The importance of the scatterer’s effective cross section when it is embedded in a random medium is emphasized. Specific results are obtained with a simple model of a scatterer.

Lamellar intrastromal corneal tattoo for treating iris defects (artificial iris)

Defects in the iris are associated with clinically significant optical anomalies, such as glare and peripheral light scatter; however, current artificial-iris technology remains inadequate. The purpose of this study was to explore the practicality of a lamellar intrastromal tattoo technique as a treatment modality to correct optical and cosmetic defects resulting from simulated iris abnormalities in eye-bank eyes. Simulated iris defects (abnormally large pupil, sector iridectomy, iridodialysis, and aniridia) were produced in a series of eye-bank eyes. Depending on the simulated iris defect, one or two lamellar channel(s) were created at 50% depth of the cornea via a peripheral incision (1.8 mm) with specialized proprietary instruments (KeraVision, Inc., Fremont, CA, U.S.A.). Commercially available tattoo pigment was inserted through the lamellar channel(s) and blended into the defective region of the iris. The tattoo treatment was relatively simple to perform. Tattoo pigment was inserted uniformly through the small incision, and adequate color blending to match the recipient iris was achieved. The intrastromal tattoo effectively obscured light. The lamellar intrastromal tattoo technique appeared to be efficacious for treating different types of iris defects in eye-bank eyes. Further investigation of this technique in nonsighted patient eyes is warranted.

Optical and magneto-optical anomalies for iron on a structured substrate

Measurements of the reflectivity and the transverse Kerr effect for sputtered iron films on flat and structured substrates reveal, for the first time, anomalies in both the optical and magneto-optical behaviour of the structured samples. The presence of anomalies in the transverse Kerr effect measurements, for various orders of diffraction, is much clearer than in those of reflectivity. The results are discussed in terms of the anticipated Rayleigh condition for optical anomalies and the condition for the generation of surface plasmons in iron.

Optical and elastic anomalies near the phase transition in

shows a structural phase transition near . The temperature dependence of the optical birefringence , of the elastic stiffness constants and of the effective electro-optical coefficients is determined. At the derivative changes its sign. Elastic properties are studied by recording the acoustic resonances of a rectangular parallelepiped. We discuss those features of the method which are important in the investigation of phase transitions. No signature of elastic softening near is observed in . Below and increase continuously. The elastic hardening is accompanied by the onset of a small electro-optical effect. Its existence demonstrates the loss of the centre of symmetry, its anisotropy is consistent with a triclinic symmetry, and its magnitude suggests a spontaneous polarization of about in the low-temperature phase. Although is reminiscent of a weak ferroelectric material there are some observations which are uncommon to a paraelectric - ferroelectric phase transition.

Optical conductivity in Mott-Hubbard systems.

We study the transfer of spectral weight in the optical spectra of a strongly correlated electron system as a function of temperature and interaction strength. Within a dynamical mean field theory of the Hubbard model that becomes exact in the limit of large lattice coordination, we predict an anomalous enhancement of spectral weight as a function of temperature in the correlated metallic state and report on experimental measurements which agree with this prediction in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$. We argue that the optical conductivity anomalies in the metal are connected to the proximity to a crossover region in the phase diagram of the model.

Optical dissymmetry in crystals due to inhomogeneous distribution of isomorphous components

The mechanisms of optical dissymmetry (optical anomalies) due to inhomogeneous trapping of isomorphous impurities into a crystal are considered using water-soluble systems of potassium dihydrophosphate-ammonium dihydrophosphate and alum as an example.

Sector growth and symmetry of (F,OH) apatite from the Asio mine, Japan

AbstractA study of apatite crystals from the Asio mine, Japan, showed sectoral texture related to the growth of the crystal, and with optically biaxial properties within the sectors. Wet chemical analysis gave a composition Ca5(PO4)3(F0.64,OH0.38,Cl0.01)1.03 for the specimen.Additional diffraction spots were not observed in precession and oscillation X-ray photographs and electron diffraction photographs. Since the internal textures correlate with the surface growth features, it is suggested that the internal textures and the unusual optical properties were produced during nonequilibrium crystal growth. The fluorine/hydroxyl sites in hexagonal apatite are symmetrically equivalent in the solid crystal but, at a growth surface, this equivalence may be lost, resulting in a reduction of crystal symmetry. Heating of the apatite to about 850°C results in the almost complete disappearance of the optical anomalies due to disordering, which may be related to the loss of hydroxyl from the crystal.

Significance of Optical and Physical Maturity Anomalies to Exploration in the Paradox Basin: ABSTRACT

Significance of Optical and Physical Maturity Anomalies to Exploration in the Paradox Basin: ABSTRACT

Streak retinoscopy. Optical principles and practical recommendations

The optical principles of streak retinoscopy are demonstrated by diagrams and by optical models. The phenomena observed in the proband's pupil are being explained in two ways: In the first explanation, the image on the proband's retina and its movements are considered, or rather their projection into space; this explanation corresponding to the term "retinoscopy" is commonly used in English textbooks. In the second explanation, the limitations of the light bundle by the proband's and the observer's pupils are considered; hence the term skiascopy (sigma kappa iota alpha = shadow), commonly used in the German literature. The practical hints include retinoscopy through the phoropter, suggestions for the examination of children both with and without cycloplegia, the measurement of accommodation, the detection of opacities and irregularities in the optical media, and the analysis of visual field defects caused by optical anomalies, such as refraction scotomas.

Phenomenological two-carrier model for oxide superconductors

A phenomenological two-carrier model for high- T c oxide superconductors is proposed on the basis of experimental results for optical conductivity. A dielectric response function is formulated for the system consisting of Drude and hopping carriers, in which relaxation and strong-correlation effects are taken into account. Given an appropriate choices for the values of effective masses, carrier concentrations and relaxation times, this dielectric function can well reproduce the experimental results for optical conductivity in La 2− x Sr x CuO 4 and YBa 2Cu 3O 7−δ. The superconducting transition temperature T c is then estimated, regarding the hopping component as a dielectric medium producing an attractive pairing force between the Drude carriers. This model can consistently account for a number of experimental facts, such as (i) optical anomalies in the mid-infrared region, (ii) high transition temperature, (iii) correlations between T c and a number of physical parameters, (iv) the significance of low dimensionality.

Anomalous optical and electrical recovery processes of the photoquenched EL2 defect produced by oxygen and boron ion implantation in gallium arsenide

The optical and electrical recovery processes of the metastable state of the EL2 defect artificially created in n-type GaAs by boron or oxygen implantation are analyzed at 80 K using optical isothermal transient spectroscopy. In both cases, we have found an inhibition of the electrical recovery and the existence of an optical recovery in the range 1.1–1.4 eV, competing with the photoquenching effect. The similar results obtained with both elements and the different behavior observed in comparison with the native EL2 defect has been related to the network damage produced by the implantation process. From the different behavior with the technological process, it can be deduced that the electrical and optical anomalies have a different origin. The electrical inhibition is due to the existence of an interaction between the EL2 defect and other implantation-created defects. However, the optical recovery seems to be related to a change in the microscopic metastable state configuration involving the presence of vacancies.

Optically Anomalous Crystals

AbstractThe optical symmetry of many crystals is lower than would be expected from their external form and X‐ray diffraction data. Recently such optical anomalies have been attributed to nonequilibrium structures resulting from kinetically controlled crystal growth. Impurities are incorporated to different extents at various surface sites that would otherwise have become symmetry‐related within the bulk crystal. After their discovery by Brewster in 1815, optically anomalous crystals were the subject of lively debate throughout the 19th century among some of the most distinguished contributors to the development of crystallography including Biot, Berzelius, Herschel, Mitscherlich, Frankenheim, Pasteur, Mallard, Klein, Groth, Wyrouboff, Barlow, Brauns, Rinne, Pockels, and Friedel. From a sea of wild speculation two conflicting postulates emerged: that the symmetric form resulted from accidental twinning of segments with lower symmetry, or that the optical peculiarities resulted from stress due to impurities or external perturbations. Neither postulate expresses the present view. Interest in this research waned at the turn of the century, and after 1917 no one pursued Tammann's alternative correct insight. The problem of anomalous double refraction attracted no attention for more than half a century until its recent solution. This review discusses both mineral and organic systems with particular emphasis on the phyllosilicate apophyllite and on 1,5‐dichloro‐2,3‐dinitrobenzene. These nonequilibrium structures relate to questions of crystal order, crystal growth, molecular recognition, and the design of new materials. The review provides a reminder of the enduring value of the polarizing microscope as a research tool in chemistry.