Refractive Index Correction Research Articles

The refractive index correction in luminescence spectroscopy

It is shown that the so-called refractive index or “ n 2” correction used when calculating luminescence quantum efficiencies is generally inappropriate. For accurate evaluations no refractive index correction is required provided that a simple modification to luminescence spectrometers is carried out.

Order sorting, focusing and polarizing monolithic monochromators for synchrotron radiation

Two novel types of monochromators which eliminate higher orders usually present in crystal monochromatized synchrotron radiation beams have been used successfully in spectroscopic studies in the 1–4 Å X-ray range. The design of the monochromators is based on the refractive index correction's dependence on wavelength and relative orientation of crystal surface to reflecting Bragg planes. The monochromators can be used to select a particular order, eliminate higher orders, to decrease or increase the reflected beam cross section by Bragg focusing, and in one type, to manipulate the polarization state of the diffracted beam. The general theory and summary of operating experience with these monochromators in synchrotron radiation studies at the 12 GeV electron synchrotron at the Wilson Synchrotron Laboratory at Cornell University and the 1.8 GeV storage ring DCI at Orsay are presented.

Correction for refractive index in the comparison of radiative lifetimes in vapour and solution phases

Different expressions in the literature for electronic transition probabilities are compared, with emphasis placed on their dependence on the refractive index n of the medium. It is shown that, in cases where the experimental integrated area under the absorption curves is essentially independent of the medium, the radiative rate constant k r should depend on n 2; this is verified experimentally in a comparison of the gas phase and solution phase fluorescence from 9-methylanthracene.

Monolithic crystal monochromators for synchrotron radiation with order sorting and polarizing properties

Two novel types of x-ray monochromators which eliminate unwanted higher orders usually present in crystal monochromatized synchrotron radiation beams have been used successfully in spectroscopic studies. The design of the monochromators is based on the refractive index correction’s dependence on wavelength and relative orientation of crystal surface to reflecting Bragg planes. In addition to the order sorting property, both types of monochromators can be used to decrease or increase the reflected beam cross section by Bragg focusing, and in one type, to determine the polarization state of the diffracted beam.

THE USE OF ATMOSPHERIC MODELS WITH TRILATERATION

In trilateration, when lengths are observed in pairs or groups, it is frequently possible to apply refractive index corrections obtained from an atmospheric model. This article presents a comparison of results using a model with those obtained from temperature and pressure measurements.

RECENT MEASUREMENTS OF THE SPEED OF LIGHT

AbstractDuring the last few years several measurements of both the frequencies and wavelengths of laser radiations have been completed, from which values of the speed of light in vacuum, c, have been deduced. A detailed review of these measurements has been given by Rowley et al.. One of the initial reasons for undertaking the new measurements was the need for an improved value of the speed of light for geodetic distance measurements using electromagnetic wave techniques. This requirement was later outstripped by the needs of laser ranging in space, where the precision of timing and the much smaller or absent refractive index correction called for a value of c as accurate as the length standard itself. In this note we briefly discuss the recent speed of light measurements and the value now recommended for general use. The measurements and their uncertainties are listed in the Table, together with the conventional value of the speed of light adopted in 1957, and the currently recommended value, proposed in...

Digital wavemeter for cw lasers*

The ratio of an unknown laser wavelength to that of a standard is quickly determined by a two-beam interferometer with a corner-cube reflector moving on an air track. Standard and unknown wavelength beams travel identical paths in opposite directions, so refractive index corrections are minimized. Accuracy is about six parts in 10/sup 8/. Absolute measurements of some iodine hyperfine component wavelengths are reported.

Absolute measurements of Brillouin-scattering efficiencies of molecular liquids*

Brillouin-scattering efficiencies of liquids were determined by use of a sample cell free from refractive-index corrections and by use of Rayleigh scattering from Ludox solution as an intensity reference. The scattering efficiencies for carbon disulfide, toluene, benzene, and carbon tetrachloride were determined at 4880 A. for 90° scattering to be 17.9 ± 1.2, 12.7 ± 1.0, 10.2 ± 0.7, and 9.72 ± 0.78, respectively (in units of 10−6 cm−1 sr−1).

An absolute measurement of the lattice parameter of germanium using multiple-beam X-ray diffractometry

The d spacing of the 355 reflexion in silicon has been compared with the d spacing of the 800 reflexion in germanium using pseudo non-dispersive multiple-beam X-ray diffractometry with Mo Ka1 radiation. This technique gives the ratio of the two lattice parameters without the need for a precise knowledge of the X-ray wavelength. Symmetric transmission geometry was used to eliminate the refractive index correction. The results were: {{d(800 Ge)}\over{d(355 Si)}} = 1.0002348 (± 0.0000006) at 22.5 °C and {{d(800 Ge)}\over{d(355 Si}} = 1.0002458 ( ± 0-0000016) at 25 °C. By using the known lattice parameter of silicon obtained by X-ray and optical interferometry it was found that the lattice parameter of germanium at 25 °C is 5.6579060 ± 0.0000092 A.

MEKOMETER III: EDM WITH SUB-MILLIMETRE RESOLUTION

The Mekometer is an electro-optic distance measuring instrument with a resolution of 0·1 mm and a maximum range of 3 km. The NPL prototype Mk III has been shown to be free from cyclical phase errors and, in addition, incorporates an automatic correction for refractive index. It has been subjected to very extensive field trials.

MEKOMETER III: EDM WITH SUB-MILLIMETRE RESOLUTION

The Mekometer is an electro-optic distance measuring instrument with a resolution of 0·1 mm and a maximum range of 3 km. The NPL prototype Mk III has been shown to be free from cyclical phase errors and, in addition, incorporates an automatic correction for refractive index. It has been subjected to very extensive field trials.

New Distance Measuring Instruments

New short range distance measuring instruments give the transportation engineer, land surveyor and geodetic engineer better accuracy, increased production and lower cost per mile of traverse projects. The Wild DI-10 and Tellurometer MA 100 instruments utilize invisible light (infrared) to measure short distances varying from 1 m to 2,000 m. Operation of either instrument is simple and straightforward with a minimum training course. Plumbing instrument and prisms precisely over the point and proper instrument alignment to the prisms is critical. Instrument constants should be checked frequently. Precise distances of 1 part in 50,000 can be measured by one employee in a short time thereby eliminating a taping crew of three to five employees. Refractive index corrections over the short distances are small and can be obtained from the graph supplied. Instruments are compact and operate from a 12-v battery.

A new method for the measurement of distances up to 5000 ft by means of a modulated light beam

The paper describes a new method of measuring long distances by means of a light ray polarization-modulated at ultra-high frequencies. The modulation wavelength is determined by reference to cavity resonators, used in such a manner that no atmospheric refractive index correction has to be applied. This leads to a very simple method of obtaining the required distance directly in feet. The theory of the method is given in detail, including the effect of altitude on the measurement. The apparatus itself is also described together with some preliminary results which illustrate the accuracy that can be achieved.

Statistical evaluation of the rotatory dispersion parameters for helical polymers and proteins: Two proposed methods and their application to data on polyglutamic acid and plasma albumin

Two statistical methods for the evaluation of the best values of the parameters of the Moffitt equation, λ 0, a 0, and b 0, are proposed. The first is based on the maximization of the F ratio of the linear regression term to the residual term in the Moffitt-Yang form of the equation. The second is based on the minimization of the quadratic term in an extended form of this equation. Both methods are readily programmed for a digital computer. The usefulness of these equations has been demonstrated by analysis of a large number of dispersion curves obtained on polyglutamic acid through the region of the helix-coil transition and on bovine and human plasma albumins as function of pH. The results clearly show the inability of the simple Drude equation to fit dispersion data on native plasma albumin even over a relatively narrow range of wavelengths, and the remarkable ability of the Moffitt equation to fit data over a much broader range. It is shown that the best values of the dispersion parameters are not altered by extending the dispersion data from 300 mμ down to 240 mμ; however, precision is actually lost by this extension of the data. The best value of λ 0 is shown to be constant within experimental error throughout almost the entire helix-coil transition in polyglutamic acid. The best value of λ 0 is not affected by omission of the correction for solvent refractive index provided that the dispersion of refractive index is simple; however, the best values of a 0 and b 0 are appreciably affected by omission of this correction.

Apparatus for the measurement of light scattering in liquids: Measurement of the Rayleigh factor of benzene and of some other pure liquids

The construction of an apparatus for measuring the scattering of light in colloidal solutions and its angular dependence is described. The optical part is designed in such a way that the photometer measures the flux of scattered light originating from a well-defined volume of liquid within a well-defined solid angle. The intensity of the scattered light is compared with a part of the primary beam in a compensator with a sensitive null-amplifier. For comparing fluxes of light scattered in different media the corrections for volume and solid angle can be combined into one refractive-index correction. Its value, for cylindrical as well as for rectangular liquid cells, is equal to the square of the ratio of the refractive indices. Absolute measurements of the Rayleigh factor of benzene with a precision of about 2.5% were made using light of three different wavelengths. Rayleigh factors of some other pure liquids were also determined. The value of Avogadro's number calculated from these results with the aid of the Einstein formula shows the reliability and accuracy of the instrument for absolute light-scattering measurements.

The turbidimetric precipitation titration of polystyrene

The turbidimetric precipitation titration of 7 fractions of polystyrene in the molecular weight range 39000 to 740000 has been studied, and the experimental requirements for reproducibility established. Calibration equations relating ( a) the concentration of precipitated polymer to the optical density, ( b) the initial precipitation point and the point of half precipitation to the polymer concentration and molecular weight, ( c) the concentration of polymer remaining in solution to the volume fraction of precipitant added, have been established for toluene solutions with methanol precipitant. These equations allow the molecular weight distribution of polydisperse polystyrenes to be calculated from their turbidimetric precipitation curves. Good agreement is shown between molecular weight distributions obtained by this procedure and those obtained gravimetrically. The relation between optical density and precipitate concentration is not linear, and cannot be linearized by use of the Rayleigh refractive index correction. The precipitate consists of coacervate drops of size from 1μ downwards. The precipitation curves of mixtures of fractions are almost additive in precipitate concentration, indicating very little interaction between polymer molecules of different sizes. The point of half precipitation is a constant multiple (1.23 in mole fraction) of the initial precipitation point for all molecular weights and concentrations.

Geons

Associated with an electromagnetic disturbance is a mass, the gravitational attraction of which under appropriate circumstances is capable of holding the disturbance together for a time long in comparison with the characteristic periods of the system. Such gravitational-electromagnetic entities, or "geons"; are analyzed via classical relativity theory. They furnish for the first time a completely classical, divergence-free, self-consistent picture of the Newtonian concept of body over the range of masses from \ensuremath{\sim}${10}^{39}$ g to \ensuremath{\sim}${10}^{57}$ g. Smaller geons are quantum objects whose analysis would call for the treatment of characteristic new effects. Topics covered in the discussion include: 1. Need for a self-consistent formulation of the concept of "body" in classical physics; geons vs free waves; electrical neutrality of geon; size and mass relations; the quantum limit and electron pair phenomena. 2. Orders of magnitude for toroidal geons; first estimates of leakage rates; a "phosphor" model of a geon; attrition and attritivity; energy action relation. 3. Idealized spherical geon; conditions required for symmetry; instability relative to pairing of light rays; time scale of instability long compared to vibration periods; spherical metric; wave equation for electromagnetic potential; evaluation of stress-energy tensor; its position as source of gravitation field; the gravitational field equations; the three equations of the self-consistent geon; simplification by scale transformation; first analysis of the eigenvalue problem; further scale transformation to get behavior of solution in active region of geon; further analysis of eigenvalue dependence; electronic calculator integration of equations of self-consistent geon; mass and radius values. 4. Transformations and interactions of electromagnetic geons; evaluation of refractive index barrier penetration integral for spherical geon; photon-photon collision processes as additional mechanism for escape of energy from system; restatement in language of coupling of characteristic modes; the thermal geon; comparison of gravitation and virtual electron pair phenomena as sources of coupling between modes; gravitational coupling and collective vibrations of geon; fission of a geon; interaction between two geons simple at large distances; orientation dependence and exponential term at intermediate distances; violent transmutation processes in closer encounters. 5. Influence of virtual pairs on geon structure; description in terms of refractive index correction; relation to photon-photon collision picture; more precise formulation via Heisenberg-Euler electrodynamics; corrections to stress-energy tensor and electromagnetic field equations. 6. Neutrino-containing geons; general similarity to electromagnetic geons; specificity of geon-geon interactions; the size subject to simple analysis unexpectedly limited by neutrino-neutrino encounters and the process $\ensuremath{\nu}+\ensuremath{\nu}\ensuremath{\rightarrow}\ensuremath{\mu}+e$; similarity of size limitation to that for electromagnetic geons; comments on present status of neutrino theory of light. 7. Electricity, Gauss's theorem, and gravitational field fluctuations. 8. Conclusions: the geon completes the scheme of classical physics; one's interest in following geons into quantum domain will depend upon one's view of the relation between very small geons and elementary particles.

The Refractive Index Correction in Light-Scattering Measurements

The Refractive Index Correction in Light-Scattering Measurements