Known Index Of Refraction Research Articles

A Study of Optical Properties of Intraocular Lenses and of Measurement of the Index of Reflection for an Unknown Liquid

In general, such methods as interferometers or wavefront sensors are commonly used for testing of an optical system and optical components. In these cases, the surrounding environments are unlikely to affect the measurements. On the other hand, intraocular lenses of hydrophilic materials with special properties experience a certain difficulty in testing the optical properties. An intraocular lens is dried in the air, which causes deformation and changes the optical characteristics such as index of refraction and thickness. Thus, it is hard to measure the optical characteristics of an intraocular lens by using common methods. In this study, a special structure is used for measuring of the transmission wavefront aberration and effective focal length of an intraocular lens of hydrophilic materials by using a Shark-Hartmann sensor among the various measuring methods. As an application of this measuring method, this study shows a simple method to measure the index of refraction of unknown liquids with a plano-convex lens with a well known index of refraction. Also, this method is used to measure the optical properties of a plano-convex such as index of refraction and curvature by using a liquid with a well known index of refraction.

Quantitative coherent diffractive imaging of an integrated circuit at a spatial resolution of 20 nm

The complex transmission function of an integrated circuit is reconstructed at 20 nm spatial resolution using coherent diffractive imaging. A quantitative map is made of the exit surface wave emerging from void defects within the circuit interconnect. Assuming a known index of refraction for the substrate allows the volume of these voids to be estimated from the phase retardation in this region. Sample scanning and tomography of extended objects using coherent diffractive imaging is demonstrated.

Bayesian assessment of uncertainty in aerosol size distributions and index of refraction retrieved from multiwavelength lidar measurements

We investigate the assessment of uncertainty in the inference of aerosol size distributions from backscatter and extinction measurements that can be obtained from a modern elastic/Raman lidar system with a Nd:YAG laser transmitter. To calculate the uncertainty, an analytic formula for the correlated probability density function (PDF) describing the error for an optical coefficient ratio is derived based on a normally distributed fractional error in the optical coefficients. Assuming a monomodal lognormal particle size distribution of spherical, homogeneous particles with a known index of refraction, we compare the assessment of uncertainty using a more conventional forward Monte Carlo method with that obtained from a Bayesian posterior PDF assuming a uniform prior PDF and show that substantial differences between the two methods exist. In addition, we use the posterior PDF formalism, which was extended to include an unknown refractive index, to find credible sets for a variety of optical measurement scenarios. We find the uncertainty is greatly reduced with the addition of suitable extinction measurements in contrast to the inclusion of extra backscatter coefficients, which we show to have a minimal effect and strengthens similar observations based on numerical regularization methods.

Monte Carlo Simulation of Radiative Heat Transfer in Coarse Fibrous Media

Direct Geometric Monte Carlo modeling of a fibrous medium is undertaken. The medium is represented as a monodisperse array, with known solidity, of randomly oriented cylinders of known index of refraction. This technique has the advantage that further radiative properties of the medium (absorption coefficient, scattering albedo, scattering phase function) are not required, and the drawback that its’ Snell- and Fresnel-generated dynamics suggest a limitation to large, smooth fibers. It is found that radiative heat flux results are highly dependent on bias in the polar orientation angle (relative to the boundary planes) of the fibers. Randomly oriented fiber results compare well to both the large (specular radiosity method) and small (radiative transfer equation) limits, while the results of previous experiments lie within the range of simulation results generated using varying degrees of orientation bias.

Landsat-5 Thematic Mapper cold focal plane characterization

The gain response of the detectors in the cold focal plane of Landsat-4 and Landsat-5 Thematic Mapper (TM) is known to fluctuate temporally. This is believed to be caused by an interference effect due to a film build-up on the cold focal plane dewar window. This paper analyses the effect using a thin-film interference model. This model relates detector gain to film thickness through indices of refraction of the materials involved. The dewar window material is zinc selenide (ZnSe) with a known index of refraction, thus the index of refraction of the film in TM band 5 and band 7 can be determined by fitting the model to the gain data from each detector. The film is found to be quite absorptive in band 7, but only slightly absorptive in band 5. Film thickness has been determined to be as much as 1400 nm from the data sample used. This model is also used to remove gain variation for gain characterization over instrument lifetime. An accurate model of this effect can improve the calibration of Landsat-4 and Landsat-5 by 3-4% in band 5 and band 7. It is also applicable to Landsat-7 Enhanced Thematic Mapper Plus (ETM+) if this thin-film build-up is present.

Oximetry based on diffuse photon density wave differentials.

The quantification of tissue optical properties for calculating blood saturation and hemoglobin concentration using measurements of diffuse photon density waves at some distance away from an intensity-modulated light source, generally requires the determination of the amplitude and phase of this light source. This determination may become a severe impediment for measurements performed in the clinical environment. In this work we extend a self-calibrating methodology developed for constant wave and modulation depth-phase measurements, to include amplitude and phase measurements of diffuse photon density waves. The method uses amplitude and phase changes of intensity modulated light, under the assumption of known index of refraction and invariant reduced scattering coefficient mu's, to quantify the absorption coefficient mu(a) without requiring initial amplitude and phase knowledge. Quantification of the mu(a) at selected time points during a measurement can then be employed to calibrate numerical solutions of the diffusion equation and compute the mu(a) for the remaining time points of the experiment. It is shown that the method is quite insensitive to the knowledge of the exact mu's value so that an assumption on the average mu's value for the tissue measured may be employed. The sensitivity of calculating blood saturation and hemoglobin concentration, as a function of the deviation of the mu's used in the calculation versus the real mu's value is investigated using simulated data. It is also demonstrated that the saturation calculation is especially insensitive to the mu's guess. The performance of the method to quantify blood oxygen saturation and the concentrations of oxy- and deoxy-hemoglobin is examined with experimental measurements at two wavelengths on specially constructed blood model phantoms. To validate the method the measurements are monitored by a time-resolved spectrometer. The method is shown to be accurate to within +/-5% in calculating blood saturation and to within +/-10% in calculating hemoglobin concentration compared to the results obtained with the time-resolved spectrometer and the expected theoretical values.

Preparation of optical quality ZnCdTe thin films by vacuum evaporation

A procedure to make optical quality thin films of Zn(x)Cd(1-x)Te by use ofvacuum evaporation of the ternary compound has been developed. Thestarting point was the preparation of the compound that was then usedas the source in a simple vacuum evaporation system. Thecharacteristics of a film containing 85% ZnTe (x =0.85) are presented. Electron microscope, atomic forcemicroscope, x-ray and optical spectral measurements were made. Theindex of refraction was determined at room temperature fromtransmittance measurements in the range of from 580 to 800 nm and wasfound to agree within 1% with values found by others for singlecrystals. We did this by assuming a Sellmeier equation and a knownindex of refraction at infinite wavelength. The calculation alsoyielded the roughness of the film.

High-resolution size measurement of single spherical particles with a fast Fourier transform of the angular scattering intensity

A technique is described and demonstrated to measure the size of spherical particles of known index of refraction by laser light scattering with an accuracy of better than 1%. This technique entails imaging the angular scattering intensity onto a photodiode array and applying a fast Fourier transform to the array output to obtain a frequency and phase corresponding to the number and angular position of the scattering lobes. Errors associated with particle trajectory effects and changes in the index of refraction are also considered. Results are not affected by the former, whereas variations of the refractive index by 2%, as may be typical, for example, of the transient heat up of a liquid hydrocarbon droplet, cause a deterioration of sizing accuracy to approximately 3%. The technique can in principle be applied in real time at data rates as high as 20-30 kHz with a modest equipment investment. Therefore, the measurement of droplet evaporation rates in dilute sprays with unprecedented accuracy appears to be feasible.

Efficient automated algorithm for the sizing of dielectric microspheres using the resonance spectrum

We describe an efficient algorithm for the sizing of single microspheres having a known index of refraction as a function of wavelength. The algorithm employs a peak-detection routine that determines several resonant frequencies in the radiation scattered from the particle. These measured resonances are then compared with entries from a library of stored resonance locations in order to determine a few neighborhoods within which the size of the particle is likely to lie. A final step finds a local minimum of the cost function within each neighborhood, and the size estimate is determined by selecting the smallest of these local minima. The algorithm has modest computational and memory requirements, and it requires no analysis of complicated features of the resonance spectrum that would call for human intervention. Hence it could be automated for nearly real-time operation using a microprocessor. When applied to the measured resonance spectrum of a fluorescent polystyrene sphere, the algorithm finds the radius with an accuracy limited only by such factors as surface roughness, asphericity, and imperfect knowledge of the refractive index. The algorithm is currently limited to use with first-order resonances.

Measurement of thin-film optical absorption at the air-film interface within the film and at the film-substrate interface

A measurement technique is described where the absorption introduced by the addition of a single-layer thin film is separated into three parts: absorption (a) within the bulk of the film; (b) at the air-film interface; (c) at the film-substrate interface. The technique employs a scanning adiabatic calorimeter to measure substrates which are partially coated on the entrance surface with films of continuously varying thickness. By measuring the absorption on the bare substrate and at various film thicknesses, and by making use of changes in relative power density within the film for λ/4 versus λ/2 optical thickness films, we have determined (a) αf, the bulk absorption coefficient of the film, (b) aaf, the specific absorptance of the air-film interface, and (c) afs, the specific absorptance of the film-substrate interface. The analysis assumes that the films are highly transparent and of known index of refraction. In addition, the film thickness must range from λ/4 to 3λ/4 optical thickness, or from λ/2 to λ optical thickness. Representative data are shown for absorptance measurements at 2.7 and 2.9 μm for a film of As2Se3 on CaF2. This example exhibits predominantly film-substrate interface absorption with very little of the absorption taking place in the bulk of the film.

Absolute Infrared Intensities of the Fundamental Absorption Bands in Solid CS2

Absolute infrared intensities have been measured for ν2 and ν3 of CS2 in the solid phase. Path lengths were measured by counting interference fringes as the solid is condensed onto a cold window. The index of refraction of the solid film is estimated from the intensity of the fringe pattern on different windows of known index of refraction. The problem of choosing a suitable background is discussed. Although two different kinds of films were formed, the intensities were identical within experimental error. The intensities found for ν2 and ν3 were 850±100 and 80 000±14 000 darks, respectively. These values are quite comparable to the intensities found in liquid CS2, and are both higher than found in the gas phase. Hence, the intensity sum rule does not hold for this crystal. The observed intensification is compared with that predicted from the simple field effect, using an elliptical cavity, and found to agree quite well. Hence, we conclude that CS2 molecules do not interact strongly in the crystal in ways which affect the intensity. The ``ideal'' behavior is tested further in a comparison of the observed frequency shift with that calculated from the Kirkwood—Bauer—Magat theory; again the agreement is quite good for ν3 where the predicted shift is large. For ν2, with a smaller predicted shift, the agreement is poor, indicating that other forces are at least as large. Finally, the infrared spectra and x-ray powder pattern are used in combination to estimate the crystal structure. Both are consistent with an orthorhombic space group D2h12, with two molecules per unit cell (a=5.45, b=8.16, and c=3.74 Å). Although this space group is not determined uniquely, the crystal splitting was calculated from the dipole—dipole model, assuming that the structure was approximately correct in locating the molecules. The calculated splitting for ν3, where it is large, agrees very well with the observed splitting; for ν2, where the calculated dipole—dipole splitting is small, the agreement with experiment is poor.

On the value of recent microscopic methods of identification used for organic substances

The value of recent methods of identification of organic substances by means of the micro melting point apparatus is investigated, using 3 groups of closely related substances (benzoic acid derivatives, barbituric acid derivatives, and sulphonamids). The experiments show that a combination of the melting point determination with an observation of sublimation and conversion during heating and, moreover, with the observation of the conversion of crystallised melting drops etc. very markedly increases the value of the determination. The preparation of derivatives from quantities below l mg can be performed more rapidly and more simply than the preparation of larger amounts. The melting point determination of the derivatives is of the greatest value for the identification of the respective substances. On the other hand, the melting point determination on eutectic mixtures of the substance in question with a test substance is found to be of much lower value as a method of identification, if there is a possibility for the occurrence of a number of closely related substances having the same melting point ; such substances often have the same eutectic melting point with the same test substance. The determination of the index of refraction of molten substances (i.e., the determination of the temperature interval within which the molten mass has the same index of refraction as a glass powder of a known index of refraction) is an excellent method of identification, since the scattering of the temperature intervals found for related substances is of the same magnitude, and for not related substances is considerably higher, than the scattering of their melting points.

EFFECT OF PARTICLE SIZE AND INDEX OF REFRACTION ON REFLECTANCE*

The effect of particle size on the reflectance of thin semitransparent layers, such as enamels, was studied by using mixtures containing opacifying particles of definite sizes in an oil of known index of refraction. The mixtures were applied on a black glass plate, and the reflectance was measured. The coefficient of scatter per unit surface of the particles was calculated and was found to decrease slowly as the particle size decreased. On the other hand, for the range of sizes studied, the reflectance of the semitransparent layer increased rapidly as the particle size decreased.