جستجوی مقالات مرتبط با کلیدواژه « Refractive index » در نشریات گروه « فیزیک »

One of the fundamental issues in physics is measuring the refractive index of materials. Knowing the magnitude of the refractive index of a material plays a decisive role in predicting its behavior and the amount of light passing through it. There are different methods for measuring the refractive index. In this work, to measure the refractive index of thin samples, a system based on the optical deflectometry method has been designed and built. The theoretical basis of the work, the effective parameters and the measurement error of the system in measuring the refractive index of thin samples with a thickness of about a few millimeters have been investigated. After optimizing the system, the magnitude of the refractive index of YAG and quartz crystal samples was measured, which are widely used in various applications. Using three lasers of helium-cadmium (blue color, wavelength 442 nm), argon ion (green color, wavelength 514.5 nm) and helium-neon (red color, wavelength 632.8), dispersion of refractive index of these two substances were measured. The measured values for the refractive index in these three wavelengths were 1.44, 1.45, and 1.37 for the quartz sample and 1.81, 1.83, and 1.73 for the YAG crystal sample.

Liquid crystals with high optical and electro-optical responses play an important role in optics and photonics. Therefore, providing a simple method to increase the optical behavior of liquid crystals under the influence of external fields can be considered one of the most challenging research areas. In this experimental work, the effects of temperature and right-handed chiral material with different weight percentages on the refractive indices and optical properties of E7 nematic liquid crystal under the influence of an external electric field were investigated. Despite the reduction of the Kerr constant with increasing the weight percentage of chiral dopants and temperature, the highest amount of optical response in the presence of the electric field was obtained for the nematic liquid crystal doped with 3% of right-handed material. In this case, the value of the Kerr constant is almost 2 times that of pure liquid crystal. This interesting result can be related to the order parameter changes caused by different molecular interactions. Thus, the results obtained in this research can be used as a simple method to increase the optical response of nematic liquid crystals in the presence of an external electric field.

In radiation calorimetry by using laser beams and interferometry setups, variations induced by dose absorption in phantom can be precisely measured. Dose absorption and the induced temperature change result in refractive index variation of the material. In order to be able to measure the low amount of absorbed dose in the phantom, temperature dependence of refractive index of the material must be precisely known. Water and Plexiglas phantoms can be used as tissue-equivalent materials and a multitude of reports have been published in recent years regarding their use for radiation calorimetry.  In this study, temperature dependence of refractive index of water and Plexiglas (poly- methyl methacrylate) is measured using a laser interferometry setup. The results show that the refractive index of Plexiglas has more variations with temperature compared to water. This shows that use of Plexiglas as the absorbing material for optical calorimetry, due to its nearly zero heat defect, increases the accuracy of absorbed dose measurements.

Using coherent light sources for manufacturing optical dosimeters is of considerable interest. Optical dosimeters are mostly employed for radiotherapy applications; where knowing the temperature dependency of refractive index of the used material in the core of dosimeter, often water, is required. In this work, by setting up and employing an interferometer in the laboratory, the temperature dependency of refractive index of water is measured. The setup is fully described and the required theoretical relations for interpreting the experimental data are developed. Comparing the results with the previous experimental data provided by other groups, demonstrats good compromise and confirms the accuracy of the measurements. It is shown that the second-order polynomial model can be efficiently used for interpreting the measurement data. The results of this study can be used in all those applications where knowing the temperature dependency of refractive index of water is a prerequisite.

Optical properties of the yttrium oxide, such as the dielectric function, refractive index and electron energy loss spectroscopy (EELS), are studied. Calculations are done by full-potential augmented plane waves (FP-LAPW) in density functional theory (DFT) framework by Wien2k package. According to EELS curve, the plasmon energy is estimated about 13eV. The obtained static refractive index is 1.92. In addition, optical conductivity diagrams show that due to the band gap at 4 eV, it is not able to excite the conduction band. The results are in good agreement with that of other theoretical and experimental works.

Solar cells have different efficiencies in different weather conditions and environments. Changing the environmental conditions leads to the change in the environmental refractive index. The change in the refractive index affects the efficiency of the solar cell. In this paper, we investigate and model the effect of changing the refractive index of the environment on a silicon solar cell with thickness of 500nm and silver ribbon nano-plates of width 25nm and height 50nm. We study the effect of refractive indices from 1 to 1.6 on the performance of the solar cell. The simulation results show that the best efficiency and absorption of plasmonic solar cell with silver ribbon nano-plates with width 25nm, height 50nm, and period 50nm are obtained in a refractive index of 1.2. The solar cell efficiency and fill factor are respectively evaluated as 12.45% and 83%. Finally, the open circuit voltage and short current density are calculated as 0.21V and 6.91mA/cm2, respectively.

In this paper, SiO2 thin film is produced by two at the first method, SiO2 is evaporated by the electron gun and oxygen gas is injected to compensate for oxygen loss due to dissociation. At the second method, silicon monoxide is evaporated by thermal evaporation and during the evaporation time, substrate is bombarded by the ion oxygen that produced by an ion source. The refraction index, the extinction coefficient and the thickness layer are calculated by numerical method of the transmittance and reflectance equations. By the shift in the spectral transmittance, amount of non uniformity is calculated. Results show that if the quantity of the current and the ion energy are selected properly, SiO2 film will not have absorption. Moreover, SiO2 film produced by the second method is more uniform than that of by the first method

In this paper, the production mechanisms and the spectral-angular distribution of X-ray Cherenkov radiation (XCR) was investigated in detail and some unique properties of XCR and its applications were discussed. It is shown that, in the vicinity of the atomic absorption edges, the real and the imaginary parts of the refractive index are varied drastically and for some materials the refractive index exceed unity and Cherenkov radiation can be generated in soft X-ray regions with a narrow band width. By selecting suitable Cherenkov emitters and using laboratory-sized electron accelerators, in the optimal conditions, the brightness of the soft X-ray source was calculated and compared to other soft X-ray sources. On the basis of these investigations, some unique properties of XCR such as, narrow band width and high brightness make XCR as a novel soft X-ray source for applications in soft X-ray microscopy, photoelectron spectroscopy and other research areas.

The effects of oxygen flow rate on refractive index of aluminum oxide film have been investigated. The Al2O3 films are deposited by electron beam on glass substrate at different oxygen flow rates. The substrate was heated to reach AWT IMAGE and the temperature was constant during the thin film growth. The transmittance spectrum of samples was recorded in the wavelength 400-800 nm. Then, using the maxima and minima of transmittance the refractive index and the extinction coefficient of samples were determined. It has been found that if we reduce the oxygen flow, while the evaporation rate is kept constant, the refractive index of Al2O3 films increases. On the other hand, reduced oxygen pressure causes the Al2O3 films to have some absorption.

In this paper we studied the focusing effect of electromagnetic wave in the two-dimensional graded photonic crystal consisting of Silicon rods in the air background with gradually varying lattice constant. The results showed that graded photonic crystal can focus wide beams on a narrow area at frequencies near the lower edge of the band gap, where equal frequency contours are not concave. For calculation of photonic band structure and equal frequency contours, we have used plane wave expansion method and revised plane wave expansion method, respectively. The calculation of the electric and magnetic fields was performed by finite difference time domain method.

A simple relation between the optical electronegativity، energy gap، refractive index and electronic polarizability is given for ternary chalcopyrite semiconductors. Energy gap has been evaluated from the optical electronegativity whereas refractive index and electronic polarizability values have been evaluated from the energy gap by proposing a linear relation between them. The calculated values are in fair agreement with the experimental values and earlier researchers. This work highlights the significance of interrelation between these parameters.

By illuminating the edge of transparent plate with a coherent quasi-monochromatic light, due to abrupt change in the refractive index at the plate boundary, diffraction pattern is formed on a screen perpendicular to the light propagation direction that can be described by the Fresnel-Kirchhoff integrals. The visibility of fringes depends on the plate thickness, refractive index, light incident angle and wavelength as the visibility is a periodic function of incident angle. By varying incident angle and counting the maximum of visibility repetition in two successive angular intervals, the plate refractive index is obtained with four digits meaningful without requiring the wavelength and the plate thickness. The Cauchy and Sellmeier dispersion relation can be obtained by refractive index measuring in some wavelengths. By knowing one wavelength, the plate thickness and other wavelengths with four digits meaningful, in micro meter regime, can be obtained. In this report the measurement of refractive indices in two different thicknesses of fused-silica and soda lime glass for He-Ne Laser, Nd-YAG Laser and four wavelengths of Argon laser is done. The experiment has been done by modest instrumentation It is shown that by using the high precision Goniometer and more sensitive CCD it is possible to measure the refractive indices, plate thickness and wavelength with six digits meaningful