Misplaced Pages

#572427

71-577: BBO may stand for: Barium boron oxide, another name of barium borate Big Bang Observer , planned space gravitational wave observatory IATA code for Berbera Airport " BBO (Bad Bitches Only) ", a song by Migos from the album Culture II Beta barium borate ( β-BaB 2 O 4 ) crystal Bundesbahn Österreich, a former name for the Austrian Federal Railways Bureau Bijzondere Opdrachten ,

142-431: A gouty joint will reveal negatively birefringent monosodium urate crystals . Calcium pyrophosphate crystals, in contrast, show weak positive birefringence. Urate crystals appear yellow, and calcium pyrophosphate crystals appear blue when their long axes are aligned parallel to that of a red compensator filter, or a crystal of known birefringence is added to the sample for comparison. The birefringence of tissue inside

213-625: A WWII Dutch secret service Bridge Base Online , for the game of bridge British Ballet Organization BBO, the ICAO code for Flybaboo Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title BBO . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=BBO&oldid=1163566254 " Category : Disambiguation pages Hidden categories: Short description

284-413: A few ways: The best characterized birefringent materials are crystals . Due to their specific crystal structures their refractive indices are well defined. Depending on the symmetry of a crystal structure (as determined by one of the 32 possible crystallographic point groups ), crystals in that group may be forced to be isotropic (not birefringent), to have uniaxial symmetry, or neither in which case it

355-415: A glass plate to generate an optical vortex and full Poincare beams (optical beams that have every possible polarization state across a cross-section). Birefringence is observed in anisotropic elastic materials. In these materials, the two polarizations split according to their effective refractive indices, which are also sensitive to stress. The study of birefringence in shear waves traveling through

426-456: A less invasive method to diagnose Duchenne muscular dystrophy . Birefringence can be observed in amyloid plaques such as are found in the brains of Alzheimer's patients when stained with a dye such as Congo Red. Modified proteins such as immunoglobulin light chains abnormally accumulate between cells, forming fibrils. Multiple folds of these fibers line up and take on a beta-pleated sheet conformation . Congo red dye intercalates between

497-410: A living human thigh was measured using polarization-sensitive optical coherence tomography at 1310 nm and a single mode fiber in a needle. Skeletal muscle birefringence was Δn = 1.79 × 10 ± 0.18×10 , adipose Δn = 0.07 × 10 ± 0.50 × 10 , superficial aponeurosis Δn = 5.08 × 10 ± 0.73 × 10 and interstitial tissue Δn = 0.65 × 10 ±0.39 × 10 . These measurements may be important for the development of

568-437: A measure of the degree of order within these fluid layers and how this order is disrupted when the layer interacts with other biomolecules. For the 3D measurement of birefringence , a technique based on holographic tomography [1] can be used. Birefringence is used in many optical devices. Liquid-crystal displays , the most common sort of flat-panel display , cause their pixels to become lighter or darker through rotation of

639-449: A plane wave of angular frequency ω can be written in the general form: where r is the position vector, t is time, and E 0 is a vector describing the electric field at r = 0 , t = 0 . Then we shall find the possible wave vectors k . By combining Maxwell's equations for ∇ × E and ∇ × H , we can eliminate H = ⁠ 1 / μ 0 ⁠ B to obtain: With no free charges, Maxwell's equation for

710-449: A polarization perpendicular to that of the ordinary ray, the polarization direction will be partly in the direction of (parallel to) the optic axis, and this extraordinary ray will be governed by a different, direction-dependent refractive index. Because the index of refraction depends on the polarization when unpolarized light enters a uniaxial birefringent material, it is split into two beams travelling in different directions, one having

781-433: A sample is placed between two crossed polarizers, colour patterns can be observed, because polarization of a light ray is rotated after passing through a birefringent material and the amount of rotation is dependent on wavelength. The experimental method called photoelasticity used for analyzing stress distribution in solids is based on the same principle. There has been recent research on using stress-induced birefringence in

SECTION 10

#1732800741573

852-745: Is a nonlinear optical material transparent in the range ~190–3300 nm. It can be used for spontaneous parametric down-conversion . Its Mohs hardness is also 4.5. The material exhibits a melting temperature of 1268 K, with anisotropic thermal expansion coefficients: α 11 = 4 × 10 − 6 K − 1 {\displaystyle \alpha _{11}=4\times 10^{-6}K^{-1}} and α 33 = 36 × 10 − 6 K − 1 {\displaystyle \alpha _{33}=36\times 10^{-6}K^{-1}} α₃₃ = 36 × 10⁻⁶ K⁻¹. Gamma barium borate, γ-BaB 2 O 4 , discovered recently,

923-441: Is a biaxial crystal. The crystal structures permitting uniaxial and biaxial birefringence are noted in the two tables, below, listing the two or three principal refractive indices (at wavelength 590 nm) of some better-known crystals. In addition to induced birefringence while under stress, many plastics obtain permanent birefringence during manufacture due to stresses which are "frozen in" due to mechanical forces present when

994-515: Is a disadvantage when used as a pigment. Silica -coated powders are available. The alkaline properties and the anodic passivation properties of the borate ion enhance the anticorrosion performance. Commonly available barium metaborate pigment comes in three grades; Grade I is a barium metaborate itself, grade II is compounded with 27% zinc oxide , and grade III is compounded with 18% of zinc oxide and 29% calcium sulfate . Barium borate shows synergistic performance with zinc borate . Barium borate

1065-413: Is a single direction governing the optical anisotropy whereby all directions perpendicular to it (or at a given angle to it) are optically equivalent. Thus rotating the material around this axis does not change its optical behaviour. This special direction is known as the optic axis of the material. Light propagating parallel to the optic axis (whose polarization is always perpendicular to the optic axis)

1136-485: Is a suitable material for high-power ultraviolet polarization optics . It can replace calcite , titanium dioxide or lithium niobate in Glan–Taylor prisms , Glan–Thompson prisms , walk-off beam splitters and other optical components. It has low hygroscopicity , and its Mohs hardness is 4.5. Its damage threshold is 1 GW/cm at 1064 nm and 500 MW/cm at 355 nm. Beta barium borate, β-BaB 2 O 4 ,

1207-406: Is at a finite angle from the direction of the wave vector resulting in an additional separation between these beams. So even in the case of normal incidence, where one would compute the angle of refraction as zero (according to Snell's law, regardless of the effective index of refraction), the energy of the extraordinary ray is propagated at an angle. If exiting the crystal through a face parallel to

1278-416: Is called "birefringent" because it will generally refract a single incoming ray in two directions, which we now understand correspond to the two different polarizations. This is true of either a uniaxial or biaxial material. In a uniaxial material, one ray behaves according to the normal law of refraction (corresponding to the ordinary refractive index), so an incoming ray at normal incidence remains normal to

1349-428: Is commonly used in biological tissue, as many biological materials are linearly or circularly birefringent. Collagen, found in cartilage, tendon, bone, corneas, and several other areas in the body, is birefringent and commonly studied with polarized light microscopy. Some proteins are also birefringent, exhibiting form birefringence. Inevitable manufacturing imperfections in optical fiber leads to birefringence, which

1420-546: Is different from Wikidata All article disambiguation pages All disambiguation pages Barium borate Barium borate was discovered and developed by Chen Chuangtian and others of the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences . Barium borate exists in three major crystalline forms: alpha, beta, and gamma. The low-temperature beta phase converts into

1491-400: Is governed by a refractive index n o (for "ordinary") regardless of its specific polarization. For rays with any other propagation direction, there is one linear polarization that is perpendicular to the optic axis, and a ray with that polarization is called an ordinary ray and is governed by the same refractive index value n o . For a ray propagating in the same direction but with

SECTION 20

#1732800741573

1562-460: Is involved. A material is termed uniaxial when it has a single direction of symmetry in its optical behavior, which we term the optic axis. It also happens to be the axis of symmetry of the index ellipsoid (a spheroid in this case). The index ellipsoid could still be described according to the refractive indices, n α , n β and n γ , along three coordinate axes; in this case two are equal. So if n α = n β corresponding to

1633-403: Is just a scalar (and equal to n ε 0 where n is the index of refraction ). In an anisotropic material exhibiting birefringence, the relationship between D and E must now be described using a tensor equation: where ε is now a 3 × 3 permittivity tensor. We assume linearity and no magnetic permeability in the medium: μ = μ 0 . The electric field of

1704-491: Is one cause of pulse broadening in fiber-optic communications . Such imperfections can be geometrical (lack of circular symmetry), or due to unequal lateral stress applied to the optical fibre. Birefringence is intentionally introduced (for instance, by making the cross-section elliptical) in order to produce polarization-maintaining optical fibers . Birefringence can be induced (or corrected) in optical fibers through bending them which causes anisotropy in form and stress given

1775-526: Is precipitated. Barium borate dihydrate loses water at above 140 °C. It is used as a flame retardant for paints, textiles, and paper. BBO is a popular nonlinear optical crystal. Quantum linked photons are producible with beta barium borate. Barium borate is a bactericide and fungicide . It is added to paints, coatings, adhesives, plastics, and paper products. Barium borate is resistant to ultraviolet radiation. It can act as UV stabilizer for polyvinyl chloride . The solubility of barium borate

1846-410: Is prepared from the solution of barium sulfide and sodium tetraborate . It is a white powder. It is used as an additive to e.g. paints as flame retardant , mold inhibitor , and corrosion inhibitor . It is also used as a white pigment . Barium borate dihydrate is prepared from the solution of sodium metaborate and barium chloride at 90–95 °C. After cooling to room temperature, white powder

1917-492: Is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking slightly different paths. This effect was first described by Danish scientist Rasmus Bartholin in 1669, who observed it in Iceland spar ( calcite ) crystals which have one of the strongest birefringences. In the 19th century Augustin-Jean Fresnel described

1988-484: Is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light . These optically anisotropic materials are described as birefringent or birefractive . The birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress . Birefringence

2059-488: Is the component for which the material has the higher effective refractive index (slower phase velocity), while the fast ray is the one with a lower effective refractive index. When a beam is incident on such a material from air (or any material with a lower refractive index), the slow ray is thus refracted more towards the normal than the fast ray. In the example figure at top of this page, it can be seen that refracted ray with s polarization (with its electric vibration along

2130-525: Is used as a flux in some barium titanate and lead zirconate EIA Class 2 dielectric ceramic formulations for ceramic capacitors , in amount of about 2%. The barium-boron ratio is critical for flux performance; BaB 2 O 2 content adversely affects the performance of the flux. Barium borate- fly ash glass can be used as radiation shielding . Such glasses are superior in performance to concrete and to other barium borate glasses. Birefringence Birefringence means double refraction. It

2201-441: The x and y axes, then the extraordinary index is n γ corresponding to the z axis, which is also called the optic axis in this case. Materials in which all three refractive indices are different are termed biaxial and the origin of this term is more complicated and frequently misunderstood. In a uniaxial crystal, different polarization components of a beam will travel at different phase velocities, except for rays in

BBO - Misplaced Pages Continue

2272-437: The 3 axes) where the refractive indices for different polarizations are again equal. For this reason, these crystals were designated as biaxial , with the two "axes" in this case referring to ray directions in which propagation does not experience birefringence. In a birefringent material, a wave consists of two polarization components which generally are governed by different effective refractive indices. The so-called slow ray

2343-479: The alpha phase upon heating to 925 °C. β-Barium borate (BBO) differs from the α form by the positions of the barium ions within the crystal. Both phases are birefringent, however the α phase possesses centric symmetry and thus does not have the same nonlinear properties as the β phase. Alpha barium borate, α-BaB 2 O 4 is an optical material with a very wide optical transmission window from about 190 nm to 3500 nm. It has good mechanical properties and

2414-707: The ambient-pressure α and β crystal phases contain only trigonal, sp hybridized, boron, BBO glass has around 40% of the boron on tetrahedral, sp hybridized, sites. In the liquid state the relative fractions of sp and sp boron are temperature-dependent, with the trigonal planar coordination favored at higher temperatures. Barium borate can be prepared by reaction of an aqueous solution of boric acid with barium hydroxide . The prepared γ-barium borate contains water of crystallization that can not be completely removed by drying at 120 °C. Dehydrated γ-barium borate can be prepared by heating to 300–400 °C. Calcination at about 600–800 °C causes complete conversion to

2485-420: The angle of incidence, the effective refractive index of the extraordinary ray can be tuned in order to achieve phase matching , which is required for the efficient operation of these devices. Birefringence is utilized in medical diagnostics. One powerful accessory used with optical microscopes is a pair of crossed polarizing filters. Light from the source is polarized in the x direction after passing through

2556-565: The axis around which it is bent and radius of curvature. In addition to anisotropy in the electric polarizability that we have been discussing, anisotropy in the magnetic permeability could be a source of birefringence. At optical frequencies, there is no measurable magnetic polarizability ( μ = μ 0 ) of natural materials, so this is not an actual source of birefringence. Birefringence and other polarization-based optical effects (such as optical rotation and linear or circular dichroism ) can be observed by measuring any change in

2627-407: The birefringence of the optic nerve fiber layer to indirectly quantify its thickness, which is of use in the assessment and monitoring of glaucoma . Polarization-sensitive optical coherence tomography measurements obtained from healthy human subjects have demonstrated a change in birefringence of the retinal nerve fiber layer as a function of location around the optic nerve head. The same technology

2698-410: The change in polarization state using such an apparatus is the basis of ellipsometry , by which the optical properties of specular surfaces can be gauged through reflection. Birefringence measurements have been made with phase-modulated systems for examining the transient flow behaviour of fluids. Birefringence of lipid bilayers can be measured using dual-polarization interferometry . This provides

2769-453: The crystal is positive (or negative, respectively). In the case of biaxial crystals, all three of the principal axes have different refractive indices, so this designation does not apply. But for any defined ray direction one can just as well designate the fast and slow ray polarizations. While the best known source of birefringence is the entrance of light into an anisotropic crystal, it can result in otherwise optically isotropic materials in

2840-422: The crystal. For most ray directions, both polarizations would be classified as extraordinary rays but with different effective refractive indices. Being extraordinary waves, the direction of power flow is not identical to the direction of the wave vector in either case. The two refractive indices can be determined using the index ellipsoids for given directions of the polarization. Note that for biaxial crystals

2911-424: The direction of the wave vector . This causes an additional shift in that beam, even when launched at normal incidence, as is popularly observed using a crystal of calcite as photographed above. Rotating the calcite crystal will cause one of the two images, that of the extraordinary ray, to rotate slightly around that of the ordinary ray, which remains fixed. When the light propagates either along or orthogonal to

BBO - Misplaced Pages Continue

2982-446: The direction of the optic axis, thus called the extraordinary ray ) is the slow ray in given scenario. Using a thin slab of that material at normal incidence, one would implement a waveplate . In this case, there is essentially no spatial separation between the polarizations, the phase of the wave in the parallel polarization (the slow ray) will be retarded with respect to the perpendicular polarization. These directions are thus known as

3053-509: The direction of what we call the optic axis. Thus the optic axis has the particular property that rays in that direction do not exhibit birefringence, with all polarizations in such a beam experiencing the same index of refraction. It is very different when the three principal refractive indices are all different; then an incoming ray in any of those principal directions will still encounter two different refractive indices. But it turns out that there are two special directions (at an angle to all of

3124-517: The divergence of D vanishes: We can apply the vector identity ∇ × (∇ × A ) = ∇(∇ ⋅ A ) − ∇ A to the left hand side of eq. 3a , and use the spatial dependence in which each differentiation in x (for instance) results in multiplication by ik x to find: The right hand side of eq. 3a can be expressed in terms of E through application of the permittivity tensor ε and noting that differentiation in time results in multiplication by − iω , eq. 3a then becomes: Applying

3195-556: The first polarizer, but above the specimen is a polarizer (a so-called analyzer ) oriented in the y direction. Therefore, no light from the source will be accepted by the analyzer, and the field will appear dark. Areas of the sample possessing birefringence will generally couple some of the x -polarized light into the y polarization; these areas will then appear bright against the dark background. Modifications to this basic principle can differentiate between positive and negative birefringence. For instance, needle aspiration of fluid from

3266-591: The folds and, when observed under polarized light, causes birefringence. In ophthalmology , binocular retinal birefringence screening of the Henle fibers (photoreceptor axons that go radially outward from the fovea) provides a reliable detection of strabismus and possibly also of anisometropic amblyopia . In healthy subjects, the maximum retardation induced by the Henle fiber layer is approximately 22 degrees at 840 nm. Furthermore, scanning laser polarimetry uses

3337-415: The image from light of either polarization, simply a relative phase shift between the two light waves. Much of the work involving polarization preceded the understanding of light as a transverse electromagnetic wave , and this has affected some terminology in use. Isotropic materials have symmetry in all directions and the refractive index is the same for any polarization direction. An anisotropic material

3408-426: The incoming face, the direction of both rays will be restored, but leaving a shift between the two beams. This is commonly observed using a piece of calcite cut along its natural cleavage, placed above a paper with writing, as in the above photographs. On the contrary, waveplates specifically have their optic axis along the surface of the plate, so that with (approximately) normal incidence there will be no shift in

3479-540: The index ellipsoid will not be an ellipsoid of revolution (" spheroid ") but is described by three unequal principle refractive indices n α , n β and n γ . Thus there is no axis around which a rotation leaves the optical properties invariant (as there is with uniaxial crystals whose index ellipsoid is a spheroid). Although there is no axis of symmetry, there are two optical axes or binormals which are defined as directions along which light may propagate without birefringence, i.e., directions along which

3550-503: The optic axis). In addition, a distinct form of double refraction occurs, even with normal incidence, in cases where the optic axis is not along the refracting surface (nor exactly normal to it); in this case, the dielectric polarization of the birefringent material is not exactly in the direction of the wave's electric field for the extraordinary ray. The direction of power flow (given by the Poynting vector ) for this inhomogenous wave

3621-448: The optic axis, such a lateral shift does not occur. In the first case, both polarizations are perpendicular to the optic axis and see the same effective refractive index, so there is no extraordinary ray. In the second case the extraordinary ray propagates at a different phase velocity (corresponding to n e ) but still has the power flow in the direction of the wave vector . A crystal with its optic axis in this orientation, parallel to

SECTION 50

#1732800741573

3692-475: The optical surface, may be used to create a waveplate , in which there is no distortion of the image but an intentional modification of the state of polarization of the incident wave. For instance, a quarter-wave plate is commonly used to create circular polarization from a linearly polarized source. The case of so-called biaxial crystals is substantially more complex. These are characterized by three refractive indices corresponding to three principal axes of

3763-414: The ordinary ray is simply described by n o as if there were no birefringence involved. The extraordinary ray, as its name suggests, propagates unlike any wave in an isotropic optical material. Its refraction (and reflection) at a surface can be understood using the effective refractive index (a value in between n o and n e ). Its power flow (given by the Poynting vector ) is not exactly in

3834-412: The phenomenon in terms of polarization, understanding light as a wave with field components in transverse polarization (perpendicular to the direction of the wave vector). A mathematical description of wave propagation in a birefringent medium is presented below . Following is a qualitative explanation of the phenomenon. The simplest type of birefringence is described as uniaxial , meaning that there

3905-420: The plastic is molded or extruded. For example, ordinary cellophane is birefringent. Polarizers are routinely used to detect stress, either applied or frozen-in, in plastics such as polystyrene and polycarbonate . Cotton fiber is birefringent because of high levels of cellulosic material in the fibre's secondary cell wall which is directionally aligned with the cotton fibers. Polarized light microscopy

3976-494: The polarization (circular birefringence) of linearly polarized light as viewed through a sheet polarizer at the screen's surface. Similarly, light modulators modulate the intensity of light through electrically induced birefringence of polarized light followed by a polarizer. The Lyot filter is a specialized narrowband spectral filter employing the wavelength dependence of birefringence. Waveplates are thin birefringent sheets widely used in certain optical equipment for modifying

4047-460: The polarization component normal to the optic axis (ordinary ray) and the other linear polarization (extraordinary ray) will be refracted toward somewhat different paths. Natural light, so-called unpolarized light , consists of equal amounts of energy in any two orthogonal polarizations. Even linearly polarized light has some energy in both polarizations, unless aligned along one of the two axes of birefringence. According to Snell's law of refraction,

4118-511: The polarization of light passing through the material. These measurements are known as polarimetry . Polarized light microscopes, which contain two polarizers that are at 90° to each other on either side of the sample, are used to visualize birefringence, since light that has not been affected by birefringence remains in a polarization that is totally rejected by the second polarizer ("analyzer"). The addition of quarter-wave plates permits examination using circularly polarized light. Determination of

4189-464: The polarization of the ordinary ray and the other the polarization of the extraordinary ray. The ordinary ray will always experience a refractive index of n o , whereas the refractive index of the extraordinary ray will be in between n o and n e , depending on the ray direction as described by the index ellipsoid . The magnitude of the difference is quantified by the birefringence The propagation (as well as reflection coefficient ) of

4260-549: The polarization state of light passing through it. To manufacture polarizers with high transmittance, birefringent crystals are used in devices such as the Glan–Thompson prism , Glan–Taylor prism and other variants. Layered birefringent polymer sheets can also be used for this purpose. Birefringence also plays an important role in second-harmonic generation and other nonlinear optical processes . The crystals used for these purposes are almost always birefringent. By adjusting

4331-409: The refracting surface. As explained above, the other polarization can deviate from normal incidence, which cannot be described using the law of refraction. This thus became known as the extraordinary ray . The terms "ordinary" and "extraordinary" are still applied to the polarization components perpendicular to and not perpendicular to the optic axis respectively, even in cases where no double refraction

SECTION 60

#1732800741573

4402-451: The selection of spermatozoa for intracytoplasmic sperm injection . Likewise, zona imaging uses birefringence on oocytes to select the ones with highest chances of successful pregnancy. Birefringence of particles biopsied from pulmonary nodules indicates silicosis . Dermatologists use dermatoscopes to view skin lesions. Dermoscopes use polarized light, allowing the user to view crystalline structures corresponding to dermal collagen in

4473-403: The skin. These structures may appear as shiny white lines or rosette shapes and are only visible under polarized dermoscopy . Isotropic solids do not exhibit birefringence. When they are under mechanical stress , birefringence results. The stress can be applied externally or is "frozen in" after a birefringent plastic ware is cooled after it is manufactured using injection molding . When such

4544-401: The slow axis and fast axis of the waveplate. Uniaxial birefringence is classified as positive when the extraordinary index of refraction n e is greater than the ordinary index n o . Negative birefringence means that Δ n = n e − n o is less than zero. In other words, the polarization of the fast (or slow) wave is perpendicular to the optic axis when the birefringence of

4615-459: The solid Earth (the Earth's liquid core does not support shear waves) is widely used in seismology . Birefringence is widely used in mineralogy to identify rocks, minerals, and gemstones. In an isotropic medium (including free space) the so-called electric displacement ( D ) is just proportional to the electric field ( E ) according to D = ɛ E where the material's permittivity ε

4686-411: The top of this page, with the optic axis along the surface (and perpendicular to the plane of incidence ), so that the angle of refraction is different for the p polarization (the "ordinary ray" in this case, having its electric vector perpendicular to the optic axis) and the s polarization (the "extraordinary ray" in this case, whose electric field polarization includes a component in the direction of

4757-459: The two angles of refraction are governed by the effective refractive index of each of these two polarizations. This is clearly seen, for instance, in the Wollaston prism which separates incoming light into two linear polarizations using prisms composed of a birefringent material such as calcite . The different angles of refraction for the two polarization components are shown in the figure at

4828-415: The wavelength is independent of polarization. For this reason, birefringent materials with three distinct refractive indices are called biaxial . Additionally, there are two distinct axes known as optical ray axes or biradials along which the group velocity of the light is independent of polarization. When an arbitrary beam of light strikes the surface of a birefringent material at non-normal incidence,

4899-491: The β form. BBO prepared by this method does not contain trace amounts of BaB 2 O 2 BBO crystals for nonlinear optics can be grown from fluxed melt of barium borate, sodium oxide and sodium chloride . Thin films of barium borate can be prepared by MOCVD from barium(II) hydro-tri(1-pyrazolyl)borate. Different phases can be obtained depending on deposition temperatures. Thin films of beta-barium borate can be prepared by sol-gel synthesis. Barium borate monohydrate

4970-448: Was produced by heating beta barium borate 900 °C under 3 GPa of pressure. It was found to have a monoclinic crystal structure. Barium borate has strong negative uniaxial birefringence and can be phase-matched for type I ( ooe ) second-harmonic generation from 409.6 to 3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large (55 °C) temperature phase-matching bandwidth. Although

5041-501: Was recently applied in the living human retina to quantify the polarization properties of vessel walls near the optic nerve. While retinal vessel walls become thicker and less birefringent in patients who suffer from hypertension, hinting at a decrease in vessel wall condition, the vessel walls of diabetic patients do not experience a change in thickness, but do see an increase in birefringence, presumably due to fibrosis or inflammation. Birefringence characteristics in sperm heads allow

#572427