Multi-angle spectrophotometric reflectance methods for determining refractive indices

Single crystals of nonlinear optical material 1-(4-methylphenyl)-3-(4-methoxyphenyl)-2-propen-1-one were successfully grown for the first time by slow evaporation method up to a dimension 25 x 15 x 2 mm 3 . Optical studies such as UV-Visible, energy band gap, refractive index, second harmonic efficiency have been performed. The UV-Visible spectrum reveals that the crystal is transparent in the entire visible region and absorption takes place in the UV-region. Using UV-Vis data, the energy band gap was found and it shows an energy band gap of 2.7eV for this material. The refractive index was measured using Brewster's angle method. The Kurtz powder second harmonic generation test shows that the compound is a potential candidate for photonic applications. From the I-V measurements the dc conductivity of these crystals has been studied and it is found to be very low. Dielectric constant, dielectric loss and ac conductivity of a grown single crystal have been studied in the frequency range 120Hz to 100 kHz at the room temperature and proper interpretations were drawn. The micro hardness test was carried out and the load dependence hardness was studied.

Optical, dielectric and surface studies on solution grown benzimidazole single crystals

The pairs of observations at non-normal incidence which specify the various reflection methods of determining the optical constants n and k are compared as to their arithmetical sensitivity to changes in n and k and hence as to their theoretical suitability. Only the simple methods which do not require polarimetric analysis are considered. The comparison of sensitivity is done by inspection of charts prepared from computed tables and which cover a wide range of n and k. A previously unnoticed property of the Fresnel equations at 45° incidence allows any method, not just one in which a ratio of reflectivities is measured, to be employed without a standard reflector. Experimental factors as well as theoretical sensitivity are considered, and the use of the Brewster angle as one observation is proposed. An exact analysis of the Brewster condition has been made, which leads to explicit equations applicable to two proposed methods. The distinction between the Brewster angle and the principal angle of incidence, which are often confused, is emphasized.

Modern optical design requires measurement of the refractive index of optical glass to the sixth or the seventh decimal place. Reflectometry represents an interesting option to go beyond the fifth decimal place, since from the literature we know that this technique can work to the fifth decimal place. In addition to that, this method does not use a large area of the sample, a condition that helps to increase the contribution of systematic errors. The techniques used to determine the refractive index of optical materials include transmission and reflection methods. The highest accuracy transmission techniques used in refractometry are: minimum deviation and critical angle goniometry, moire deflectometry, and interferometry. The main systematic errors that limit the measuring accuracy of each of these techniques are mentioned. The techniques used for the determination of the refractive index of optical materials from measurements of the ratio of the reflectance coefficients of its surface are widely used. Many of these methods rest on simplifications of Fresnel equations at specific angles of incidence. The geometries used include: normal incidence, 45 degree(s), Brewster angle, and other angular positions related with the specific sample to be evaluated. The analyses reported in the literature contain just the parameters present in the simplified formulas obtained for the Fresnel coefficients of each specific configuration. In this work a more complete analysis of these techniques is presented.

Monophasic Ba2NaNb5O15 was crystallized at nanometer scale (12-36 nm) in 2BaO-0.5Na(2)O-2.5Nb(2)O(5)- 4.5B(2)O(3) glass system. To begin with, optically transparent glasses, in this system, were fabricated via the conventional melt. quenching technique. The amorphous and glassy characteristics of the as-quenched samples were respectively confirmed by X-ray powder diffraction and differential thermal analyses. Nearly homogeneous distribution of Ba2NaNb5O15 (BNN) nanocrystals associated with tungsten bronze structure akin to their bulk parent structure was accomplished by subjecting the as-fabricated glasses to appropriate heat-treatment temperatures. Indeed transmission electron microscopy (TEM) carried out on these samples corroborated the presence of Ba2NaNb5O15 nanocrystals dispersed in a continuous glass matrix. The as-quenched glasses were similar to 75% transparent in the visible range of the electromagnetic spectrum. The optical band gap and refractive index were found to have crystallite size (at nanoscale) dependence. The optical band gap increased with the decrease in crystallite size. The refractive indices of the glass nanocrystal composites as determined by Brewster angle method were rationalized using different empirical models. The refractive index dispersion with wavelength of light was analyzed on the basis of the Sellmeier relations. At room temperature under UV excitation (355 nm) these glass nanocrystal composites displayed violet-blue emission which was ascribed to the defects states.

Relation among optical, thermal and thermo-optical properties and niobium concentration in tellurite glasses

The photochemical decomposition of the ionic thallous azide to metallic thallium and nitrogen has been studied as a function of wavelength, temperature and light intensity. Two values have been obtained for the activation energies; 0⋅33 eV corresponding to the full output of a mercury lamp, and 0⋅14 eV for light in the wavelength region 3200 to 3800 Å. The quantum efficiency at 3650 Å is 2×10 -3 . Two exciton bands at 3415 and 3348 Å have been observed in thallous azide by the method of low-temperature spectroscopy developed by Nikitine and Gross. Two narrow bands have been resolved in silver azide which is also an ionic azide, in the region previously studied by McLaren & Rogers. These bands occur at 3608 and 3590 Å. The refractive index of thallous azide has been measured by the Brewster angle method, and the electron energy levels have been estimated. The results of the photochemical decomposition of thallous azide have been related to the electron energy levels, and to measurements of photoconductivity made by Evans & Yoffe.

Liquid refractometers are often used in the optical industry. Although there are some liquid refractometers available, such as, the Pulfrich refractometer,1 the Abbe refractometer,1 and the Hilger-Chance refractometer,1 all of them are based on the measurement of the critical angle or the deviation angle using a microscope or a telescope. The measuring process is tedious. Some other techniques for measuring the refractive index of a liquid include, for example, the interferometric method2,3 and the Brewster angle method.

Yb is a good candidate as a pump source because there are only two manifolds in the Yb energy level scheme, the F7/2 ground state and the F5/2 excited state, and thus concentration quenching and excited-state absorption should not affect the lasing or the excitation wavelength [1]. Extensive investigations have been of Yb-doped glasses, fibers, and crystals [2–5]. The relatively long fluorescence lifetime, as well as the broad absorption and emission bands, is more prominent for Yb-doped glasses than for crystals, making the glasses attractive for diode-pumped generation of ultra-short pulses, high-power ultra-short pulse amplification and tunable laser sources [6]. In addition, the ability to achieve high concentrations of Yb ions and low loss also triggered the rapid development of various Yb-doped glasses such as phosphate, borate, and silicate glasses. However, up to now, there are few systematic investigations of the optical properties of Yb-doped germanate glasses. In this work, the spectroscopic properties of germanate glasses with different concentrations of Yb ions and different thicknesses were investigated. Glasses with compositions (mol%) 10Na2O–60GeO2– 30PbO–xYb2O3 (x = 0.2, 0.6, 1.0, 1.4, and 2.0) were prepared using regent-grade powders Na2CO3, Pb3O4, and high purity GeO2 (>99.999%). Yb 3+ was introduced as Yb2O3 with 99.9% purity. Batches of 20 g were well mixed in appropriate proportions and melted at 1050 C in a covered alumina crucible in a SiC-resistance electric furnace. The liquids were held for 15 min and the homogenous bubble-free melts were cast on a stainless plate preheated at about 150 C. The samples were well annealed in a muffle furnace to reduce thermal stress. The annealed samples were cut using a low-speed diamond saw and polished with 5 lm diamond paste. Plates of dimensions 20 mm · 10 mm · 2 mm with two polished faces were used for optical measurements. The refractive index of the studied glass was measured using the Brewster angle method. The density of the sample was measured using the Archimedes’ liquidimmersion method on an analytical balance with a precision of 0.0001 g. Absorption spectra of the glass sample were recorded with a Perkin-Elmer-Lambda 900UV/VIS/NIR spectrophotometer in the range 850–1100 nm. Fluorescence measurements were performed with a 940 nm diode laser excitation and detected by a TRIAX550 spectrophotometer controlled by a computer. The infrared fluorescence lifetime was determined by modulating the pump laser diode drive current with a square-pulse duration of 40 ms at a repetition of 10 Hz. All the measurements were performed at room temperature. The important spectroscopic parameters required include the effective emission and absorption cross sections of the F5/2 fi F7/2 transition and the upper laser level lifetimes of Yb. The emission cross section can be determined by either the method of reciprocity or the Fuchtbauer–Ladenburg formula. On the basis of the reciprocity method described by McCumber [7], the emission cross section, remi can be calculated from the measured absorption cross section, rabs, i.e.

Novel polarimetric method for determination of the Brewster angle of a dielectric

Er3+-doped tellurite glasses with various compositions (in mole%): 54TeO2-(41-x)ZnO-xBi2O3-2Na2O-3Er2O3 (x = 1, 2, 3, 4, and 5) were prepared with melt quenching method. Studies was aimed at investigating the effect of Bi3+ ion content on the physical and optical properties of the glasses. The density, refractive index, optical absorption, and optical energy band gap measurements were carried out at room temperature using pycnometer, Brewster angle method, and UV-VIS-NIR spectrophotometer, respectively. From the experiment, it was shown that the density and refractive index of the glasses increased with the increase of Bi3+ ions concentration. The absorption band intensity of electronic transition from 4I15/2 to 4H11/2 exhibited an increase as the Bi3+ ions concentration increase suggesting that incorporating Bi3+ ions into this glasses might improve the pumping efficiency.

Gibbs monolayers of lipophilic tetraphenylporphyrinatomanganese(III) and hydrophilic diacid of meso-tetrakis(4-sulfonatopheny)porphyrin adsorbed at the liquid-liquid interface have been analyzed by UV-visible external reflection (ER) and partial internal reflection (PIR) spectra measured at different angles of incidence. The angle-dependent ER and PIR spectra over the Brewster angles (thetaERB and thetaIRB) have readily been measured at the toluene/water interface. As preliminarily expected in our previous study, the present study has first proved that the reflection-absorbance of UV-visible PIR spectra quantitatively agrees with the theoretical calculations for the Gibbs monolayer over thetaIRB. In addition, it has also been proved that the absorbance of the PIR spectra is greatly enhanced in comparison to that of the ATR spectra. The enhancement is caused by an optical effect in the monolayer sandwiched between two phases of toluene and water that have different but refractive indices close to each other. This optical enhancement requires an optically perfect contact between the phases, which is difficult to prepare for a solid-solid contact. At the liquid/liquid interface, however, an ideal optical contact is easily realized, which makes the enhancement as much as the theoretical expectation. The PIR spectrometry will be recognized to be a new high-sensitive analytical tool to study Gibbs monolayer at the liquid/liquid interface.

The refractive indices along arbitrary wave vector are analyzed in a uniaxial crystal with buried optical axis. According to the Brewster angle law, the relations between the Brewster angles of the incident p-polarized light and the two principal refractive indices are obtained for the case that the optical axis is in the incident plane. Further, for the case of unknown optical axis, the two principal refractive indices and the direction of optical axis can be calculated by inserting the experimental Brewster angles into the specially derived equations. On the other hand, the functions for the reflectivity fitting corresponding to two cases, i.e. , s-polarized light and p-polarized light, are presented. Finally, the CaCO₃ crystal has been measured both in s-polarized light and p-polarized light with a view to carefully study the effect of incident angle on reflectivity. The accuracy of our measurement is able to reach 0.0001 without the need of any machining process on the sample.

Crop residues left in the field after harvest can be important in controlling soil erosion. Current methods for quantifying percent crop residue cover are tedious and somewhat subjective. There is a need for new methods to quantify residue cover that are rapid, accurate, and objective. We evaluated reflectance and fluorescence techniques for discriminating crop residues from a wide range of soils. Reflectance and fluorescence spectra of 37 agricultural soils (wet and dry) and of recently harvested and weathered corn (Zea mays L.), soybean [Glycine max (L.) Merr.], sorghum [Sorghum bicolor (L.) Moench], and wheat (Triticum aestivutn L.) residues were measured in the lab. Reflectance factors in the visible or near‐infrared wavelengths did not uniquely distinguish all soils from all crop residues. Crop residues may be brighter or darker than a given soil, depending on soil moisture and residue age. When illuminated with ultraviolet radiation, however, the crop residues fluoresced more than most of the soils. Fluorescence of crop residues was a broad‐band phenomenon centered between 420 to 520 nm and induced by a relatively broad range of excitation wavelengths centered betweert 350 to 400 nm. More than 90% of the crop residues <2 yr old could be discriminated from 33 of 37 dry soils and 36 of 37 wet soils using fluorescence. The threshold for discrimination can be optimized for classification accuracy for each soil. Fluorescence techniques are less ambiguous than reflectance methods and are better suited for discriminating crop residues on soils. Furthermore, if properly implemented, fluorescence techniques can be used to quantify crop residue cover in the field.

The scattering properties and regularity of high power microwave propagation on the jungle-ground are analyzed with finite difference time domain (FDTD) method. The scattering properties at different incident angles are obtained, and the relationship between jungle scattering coefficient and grazing angle are comparatively analyzed with analytic and numerical methods. The theoretical analysis and numerical computation indicate that the scattering coefficient curve has a Brewster angle. Larger electrical parameters of topography lead to smaller Brewster angle. When the grazing angle is less than the Brewster angle, the scattering coefficient decreases with the grazing angle increasing; when the grazing angle is greater than the Brewster angle, the scattering coefficient increases with the