scholarly journals The refractive index along the optic axis of the bovine lens

Eye ◽  
1995 ◽  
Vol 9 (6) ◽  
pp. 776-782 ◽  
Author(s):  
B K Pierscionek
Keyword(s):  
Refractive Index ◽  
Optic Axis ◽  
Bovine Lens

The Effect of Refractive Index of the Medium on the Position of the Camera Lens in Schlieren Optics

1973 ◽  
Vol 51 (20) ◽  
pp. 3309-3312 ◽  
Author(s):  
L. Ivan Epstein ◽  
Percival Nixon ◽  
Alfred J. Richard
Keyword(s):  
Refractive Index ◽  
Linear Relation ◽  
Large Change ◽  
Optic Axis ◽  
Liquid Column ◽  
Camera Lens ◽  
Component Systems ◽  
Schlieren Optics

A linear relation has been established between the plane of focus for schlieren optics in the ultracentrifuge cell along the optic axis, and the refractive index of the liquid contained in the cell. Such a relation shows that there occurs a defocussing effect when a large change in refractive index is generated in the liquid column during centrifugation of multi-component systems.

The measurement of large optic axial angles with the universal stage

1966 ◽  
Vol 35 (273) ◽  
pp. 763-769
Author(s):  
M. Munro
Keyword(s):  
Refractive Index ◽  
Rapid Method ◽  
High Refractive Index ◽  
Optic Axis ◽  
Relative Speed ◽  
Accuracy And Precision ◽  
Direct Location ◽  
Speed Accuracy ◽  
Universal Stage ◽  
Low Refractive Index

SummaryA comparison has been made of the relative speed, accuracy, and precision of several methods of measuring large optic axial angles with the universal stage. It is concluded that a method based on the direct location of a single optic axis and the application of the Biot-Fresnel law will frequently be the most satisfactory when only the standard, low refractive index centre plate for the stage is available. If a centre plate of high refractive index is employed, however, good results can normally be obtained by using the more rapid method based on the direct location of both optic axes.

scholarly journals Three-dimensional birefringence imaging with a microscope tilting-stage. I. Uniaxial crystals

2006 ◽  
Vol 39 (3) ◽  
pp. 326-337 ◽  
Author(s):  
L. A. Pajdzik ◽  
A. M. Glazer
Keyword(s):  
Refractive Index ◽  
Polycrystalline Material ◽  
Three Dimensional ◽  
Preferred Orientation ◽  
Optic Axis ◽  
Crystalline Material ◽  
Stage I ◽  
Specific Group ◽  
Optical Indicatrix ◽  
Crystalline Materials

The development of a microscope tilting-stage suitable for use with birefringence imaging is described, thus enabling precise three-dimensional birefringence information of uniaxial crystals to be obtained. Equations have been derived for uniaxial crystals in any orientation. The technique enables precise values of the birefringence Δn=ne−no(difference between extraordinary and ordinary refractive index) and orientation of the optic axis to be obtained. The sign of the optical indicatrix may be unambiguously identified. The method is also able to obtain information on preferred orientation in a polycrystalline material. In addition to this, an unknown crystalline material may be identified, or at least classified within a specific group of crystalline materials.

Design of graded-index lenses in the superposition eyes of scarab beetles

1981 ◽  
Vol 294 (1075) ◽  
pp. 589-632 ◽  
Keyword(s):  
Refractive Index ◽  
Focal Plane ◽  
Focal Point ◽  
Image Plane ◽  
Optic Axis ◽  
Clear Zone ◽  
Crystalline Cone ◽  
Screening Pigment ◽  
Corneal Lens ◽  
Intermediate Image

Superposition-image quality in the clear-zone eye depends in the first instance on the optical characteristics of the lens elements in each ommatidium. The optical design strategy of the two lens elements, a thick corneal facet and an underlying crystalline cone, in the scarab eye is reported. The formation of a good superposition image at the rhabdom layer in the eye demands that the lens elements be precisely arrayed, virtually free of optical aberrations, and that each lens pair function as an afocal (telescopic) lens system with an internal intermediate focal plane. The optical properties of the corneal facet were examined by a variety of means. The isolated corneas of most scarab species focused good quality images of a distant object. Cardinal-point analysis of the intact corneal lens revealed that the back focal point of the lens lies just proximal to the inner corneal surface, many micrometres distal to the rhabdom layer, and the position of the principal planes suggested that the corneal lens had internal lens-cylinder properties. This was confirmed by the examination of the focusing power of transverse lens slices of known thickness; the power of the corneal lens slice was a function of its thickness. Interference refractometry of corneal sections revealed that the facet is a graded-refractive-index (g.r.i.) lens in the great majority of more than 40 scarab species examined. The position of the back focal point is achieved in a thick corneal lens by (i) the presence of a g.r.i. lens, best developed in the proximal corneal region, where it consists of a g.r.i. lens cylinder capped by a g.r.i. lens hemisphere, and (ii) the loss of front facet curvature in the homogeneous distal corneal region. In situ , the back focal point lies deep within the crystalline cone. Since the quality of the superposition image depends on the exact location of the intermediate-image plane in the crystalline cone, this position was determined from a comparative analysis of cone shape, experimental observations, and theoretical modelling of the cone. Four observations, namely the presence of a waist in the crystalline cone of many species, the back focal distance of the isolated cornea when the refractive index (r.i.) of the medium in the back focal space approximated that situ, the presence of screening pigment around specific regions of the crystalline cone and the position of the intermediate-image plane in the exocone of a passalid beetle eye, all suggested that the intermediate focus lies in the waist region. The proximal region of the crystalline cone was modelled on the basis of its known g.r.i. lens properties. The model used comprised a radial g.r.i. lens cylinder with a parabolic profile in r.i., terminating in a g.r.i. lens hemiellipsoid. Dimensions and r.i. distribution in the model were based on values from real cones. The model cone focused an incident parallel beam to a point within the cone corresponding to the waist region in real cones. For beams at angles as great as 20° to the optic axis, aberrations in the model cone are small, and restricted to the most peripheral rays. A homogeneous hemiellipse of similar dimensions has severe aberrations for beams at an angle to the optic axis. The model predicts that the ommatidial optics are diffraction-limited; the spread of rays leaving the proximal cone tip due to diffraction at the small exit aperture of the cone (for all aperture diameters) is broader than that due to lens aberrations. Consequently, tolerance exists to optical imperfections in the lens components and their spacing. A tolerance in the position of the intermediate focal plane of + 2-3 pm was calculated. Lens design is strongly correlated with the daily activity pattern of the scarab species under consideration. The corneal facets of nocturnal and crepuscular species are wide with little individual facet curvature; such ‘glacial’ corneas are completely transparent. The crystalline cone is large and well developed. In diurnal species, the corneal facets are narrower, with strong individual curvature, and the corneal lens cylinders are often lined with a brown screening pigment. The crystalline cones of diurnal scarabs are frequently strongly waisted or greatly reduced in size. Pigment surrounding the cone waist serves as a field stop limiting the angular acceptance of the ommatidial optics. The waist limits the number of ommatidia that can contribute to the superposition image and therefore determines the maximum aperture of the eye. This aperture is greatest in nocturnal species with little or no waist constriction in the crystalline cone. Most scarab clear-zone eyes are of the eucone type (separate crystalline cone). However, in the Passalidae and bolboceratine and pleocomine Geotrupidae, the crystalline cone is replaced by a corneal g.r.i. lens extension, the exocone, that serves as an optical analogue of the crystalline cone.

Determination of the optic axial angle of biaxial crystals in parallel polarized light

1906 ◽  
Vol 14 (65) ◽  
pp. 157-159
Author(s):  
John W. Evans
Keyword(s):  
Refractive Index ◽  
Polarized Light ◽  
Optic Axis ◽  
Original Position ◽  
Axial Angle ◽  
Axis Of Rotation ◽  
Axis Parallel ◽  
Made In ◽  
The Revolution

It will in the first place be assumed for the sake of simplicity that the crystal to be investigated is immersed in a liquid having a refractive index as nearly as possible equal to the intermediate refractive index (β), so that light travelling along the optic axis t is not appreciably refracted on entering or leaving the crystal.The observation is made in parallel ight between crossed nicols, which are rotated together till a position of extinction is reached, when the directions of vibration of the nicols wilI be parallel to those in the crystal. If the latter be now rotated on an axis parallel to one of these directions, it will in general show light throughout the revolution, except in the original position and that opposite to it. Occasionally, however, it will remain dark throughout; in that case the axis of rotation is the bisectrix of an optic axial angle.

Optical absorption and dispersion in molybdenum disulphide

1965 ◽  
Vol 284 (1398) ◽  
pp. 402-422 ◽  
Keyword(s):  
Refractive Index ◽  
Optical Absorption ◽  
Impurity Content ◽  
Optic Axis ◽  
Oscillator Strengths ◽  
Molybdenum Disulphide ◽  
Absorption Bands ◽  
Long Wavelength ◽  
Temperature Range ◽  
Wavelength Side

The optical absorption spectrum of cleaved single crystals of molybdenum disulphide has been measured over the temperature range 290 to 77 °K. The absorption coefficients throughout the absorption region have been determined from transmission measurements on seventy crystals ranging in thickness from 0.03 to 50 μm. At wavelengths greater than 0.55 μm thin crystals do not show the normal exponential relation between transmission and thickness. At 125 °K the long wavelength absorption edge consists of two series of exciton absorption bands A n and B n (5 lines and 4 lines respectively) represented by the equations V A n ═ 16280 – 430/ n 2 cm -1 and v n B ═ 18579 – 1099/ n 2 cm -1 . To the short wavelength side of B n two absorption bands C and D occur at ca . 0.5 and 0.4 μm. Absorption bands C' and A' which occur to the long wavelength side of C and A respectively are associated with the impurity content of the natural molybdenite crystal. The single crystal reflexion spectrum has been measured at 290, 173 and 77 °K for a cleaved surface and a surface containing the optic axis. The spectra are similar, the freshly cleaved surface showing reflexion peaks associated with absorption bands A 1 B 1 C', C and D . The ordinary refractive index has been measured in the region of high absorption (5x10 5 cm -1 ) by using the interference fringes in thin crystals. The values obtained agree with those calculated from the reflexion spectrum. The dispersion of the ordinary refractive index is given by a Drude equation containing terms for absorption bands A 1 B 1 C' C and D . The oscillator strengths of each of these bands a t 77 °K has been determined. The birefringence has been measured and compared with a calculated value. The electrical conductivity, along and perpendicular to the optic axis, has been measured over the temperature range 230 to 500 °K and the activation energies of conduction found to be 0.874 eV (intrinsic) and 0-082 eV (impurity). The spectral distribution of photo-current has maxima at the wavelengths of absorption bands A 1 B 1 , C and D . An energy level diagram has been proposed to account for the optical and electrical properties of molybdenum disulphide.

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