The transmission characteristics of the dielectric grating - thin metal film - dielectric grating structure have been analyzed
by the coupled wave method (CWM). The analysis is conducted for waves of TE and TM polarizations. The qualitative
transmission characters are similar for two polarizations, but are different quantitatively. The reflectance of such structure
can be higher than 0.85 on wavelength of 1.5μm at certain parameters for a silver film with thickness of 0.0385μm. The reflectance
on the wavelength of the maximum transmission is actually equal to zero. The only thin film without gratings on
the same wavelength has the transmittance of 0.004 and reflectance of 0.984. The system, which consists of grating from
metal included between homogeneous dielectrics, also possesses by anomalous high transmission. At that the transmission
is substantially higher than a ratio of a metal-free space to the grating period. Similar dependences can be obtained for a
structure, in which the thin film of metal is located between two layers of dielectric with high refraction index. At certain
conditions the reflection is less than 0.0002 and transmission is more than 0.87 for the metal thickness of 0.0385 μm. The
rule is found, which is enable to find approximately the parameters for these high transmission structures. This effect is explained
by the coupled wave resonance with forming of a wave node within the thin metal film that minimizes absorption.
The analysis of the transmission of system "dielectric grating- thin metal film-dielectric grating-substrate" is conducted by method of coupled waves. The 53 diffraction orders are used at the analysis that ensures the suitable precision of numerical calculations. It is reveal, that at the certain parameters the system has the anomalously high transmission for the reflection of about zero. For example, the silver film with thickness of 0.0385 μm, which is placed between a two grating with the certain parameters, transmits more than 0.86 and 0.83 for TE and TM polarizations, respectively, at wave-length of 1.5 μm. Under vacuum the silver film of the same thickness has the reflection more than 0.98 and transmits less than 0.004. The analogical results are obtained for other metals: cold and potassium. The transmittance value sharply decreases at deviation of wavelength from optimum magnitude. Basing on such structures it is possible to build the narrow-banded filters. The effect of great transmission can be explained in the following way. The gratings serve as matched elements of impedance for the thin metal film and of impedance for homogeneous mediums. The field distribution inside structure meets standing wave, node of which placed on thin metal film that leads to low absorption.
The light diffraction on dielectric grating placed on metallic substrate by the method of coupled waves (CWM) taking into account the 53 diffraction orders is analysed. The modified stable S-algorithm is used for diffraction analysis. At certain parameters of grating the resonance of coupled waves (CWR), which consists in sharp increase of electromagnetic field into grating, appears. This increase of electromagnetic field results in full absorption of wave energy in metallic substrate. The behaviour of CWR depends on modulation value of permittivity of grating material. The approximate grating parameters at the condition of appearance of waveguide effect corresponding to CWR are found. These parameters are improved for achievement of full absorption by the picking-up method. The grating parameters on platinum, potassium, gold, silver for wavelengths of 0.85 μm and 1.5 μm at condition, that reflection coefficient less that 0.0001, by CWM are found. For Pt and K the dependencies of reflection coefficient on the grating thickness for TE and TM polarisation are obtained. For all metals dependencies of reflectance on wavelength, which it is possible rather precisely to describe by analytical equations with a Laurence's function, are calculated. Especially, analytical dependence precisely coincides with a curve, which by CWM for grating with small permittivity modulation of grating material is obtained. For potassium and silver the dependence of reflectance on light incidence on grating is obtained. The analysis of resonance absorption effect for TE and TM polarisation is conducted.
In the classic method for calculation of energy-band structure of photonic crystal the electromagnetic field of wave that propagates in crystal is expanded in plane waves. The determination task of the allowed frequencies at certain wave vector in the first Brillouin zone leads to the finding of eigenvalues and eigenvectors of the corresponding matrix equation with dimension, which provides the necessary precision of determination of the allowed frequencies. Because of slow convergence of expansion in plane waves, it is necessary to solve the matrix equation of high dimension that requires considerable computation time. The proposed method of determination of the allowed frequencies is based on the coupled wave method (CWM) at the corresponding definition of boundary periodic conditions. Especially, this method is simple for 1D photonic crystals, that comes to the eigenvalue problem of the matrix equation of 2x2 dimension. For 2D photonic crystals the solution also leads to the eigenvalue problem, but of 2Nx2N matrix, where N is number of the coupled waves. Frequency will be allowed, if absolute value of eigenvalue is equal to one. In the proposed method the 2Nx2N dimension of the matrix equation is equivalent to the dimension of N2xN2 of classic method. The stable S-algorithm of computation is developed. The computations of energy-band structure of 1D and 2D photonic crystals of the simplest structure are conducted. The dependencies of computation precision on the number of coupled waves at change of N from 1 to 29 are obtained.
The results of investigations on transmission spectrum of identical Bragg grating system in an optical fiber are presented. A controllable interferometer with resolution of 0.1 pm in linewidth of 1550+1nm can be built from four gratings.
In order to form flat-panel displays with a high resolution property, the phosphor layer should possess considerable electrical conductivity and thermal stability. Thin phosphor films of zinc silicates, rare earth galats and/or multilayer system on their ground are known to satisfy these very requirements. The authors choose the following compounds of ZnSiO4:Ti, ZnSiO4:Mn, Zn0.4Gd1.6O3:Eu, KGa5O8:Mn with the corresponding color gamma luminescence as the targets for laser pulse deposition based on the above mentioned reasons. The main results on the research physical-technological conditions of the thin phosphor compound film synthesis of the of ZnSiO4:Ti, ZnSiO4:Mn, Zn0.4Gd1.6O3:Eu, KGa5O8:Mn obtained by means of the reactive laser pulse evaporating with the help of quasi-closed reactive ambience are given in this work.
Peculiarities of light diffraction on multilayered holograms have been analyzed based on the coupled waves theory. For such holograms, oscillations with periods determined mainly by distances between subholograms are observed in the dependence of diffraction efficiency on incident angle. If a refractive index modulation efficiency for two-layered holograms is more than a definite quantity then it is possible to match an incident angle for each wavelength of a definite range (i.e. 0.4 . . . 0.8 mkm) and the diffraction efficiency at such an angle is 100% and it does not have to be a Bragg angle. Such multilayered holograms can be used in laser technology for wavelength selection instead of the Fabry-Perot interferometer in semiconductor laser frequency stabilization devices, and for small angle displacement measurements.
The technique for high precision measurement of optical absorption and adsorption is proposed. The technique is based on the laser interferometric calorimetry method. The mathematical model for estimation of thermal fields which occur in the sample at partial absorption of high-power laser radiation is elaborated. The model considers influence of volumetric and superficial optical absorption coefficients. Sensitivity of measurement technique of absorption coefficients for optically transparent materials is (10-3 divided by 10-7) cm-1. The results of experimental tests of optical material for visible spectrum are shown.
Three types of periodical structures formed on fibre cladding are observed. First one formed on the fibre cladding, which resulted in refractive index changes along fibre axis, second one formed as corrugated boundary between fibre core and cladding, and third one created on the fibre cladding as corrugated periodical grating. Sensitivity and characteristics of such structures are shown. Finally, achieved results are considered and analysed.
Results of development of high-sensitive method of absorption coefficient measurement of lasers resonator mirrors that bases on use of interferometric calorimetry are presented in given work. Essence of method consists in the measurement of deformation of mirror surface in the result of its local heating at incidence of powerful laser beam. Investigated mirror is part of high q-factor Fabry-Perot interferometer and, in the same time is intrinsic resonator of powerful laser, for increasing of method sensitivity.
The proposed technique is targeted at high accuracy measurement of absorbing ability of optical materials with use of laser interferometer calorimetry. The mathematical model of estimating of thermal fields, which arise in a sample at partial absorption of powerful laser radiation, allows us to divide influence of coefficients of superficial and volumetric absorption. Using the high capacity CO-laser for material heating makes it possible to reach measurement sensitivity of (10-3 divided by 10-7) cm-1 of measuring of absorption coefficients of optically transparent materials. The separation of superficial and volumetric absorption allows to test quality of processing of optical elements, and thus, to predict beam durability of materials, avoiding to their physical destruction.
In papers it is considered the possibility of the realization of the linear parameter transformers and radio frequency meters with using of the acoustooptic modulators based on the manipulations by the optical phase images of their copies laboratory investigations are carried out for the phase gradient visualization along the direction of the acoustic waves propagation.
Research possibility of application of optical-digital system, including CCD-camera for the determination of the surface form and geometric parameters of microlenses. It is shown that microlenses have a shape of the cut sphere. Approximate polynomial describing surface of microlens is calculated and main geometric parameters of these optical elements, the curvature radius, diameter and height of microlens are calculated.
The sensor described here enables measurement of temperature avoiding semiconductor-fiber coupling losses as we have in conventional fiberoptic temperature sensor. Response time of the sensor increases and it is rugged and inexpensive.
Theoretical calculations provided for further elaboration of sensitive elements for fiberoptic sensors of physical values are stated at present paper. Technological possibilities of such element creation and their further application are considered. Theoretical analysis shown that reflection coefficient from fiber cladding gratings is balanced with different types of gratings because of possibility of creation of considerable equivalent periodical change of refractive index, though optical wave amplitude on the fiber cladding less than on the fiber core. Fiber cladding gratings can be formed by holographic method using photosensitive medium and blue-green lasers. The case of corrugated boundary between fiber core and cladding or between fiber cladding and external medium, for e.g. water contaminated by particles of heavy metals, which have influence on refractive index and absorption of waves in fiber is possible.
Some of the optical devices work on the basis of light extension in the dielectric environment with refractive index as a periodical function. The following devices belongs to such class: interference filters on reflection, deep holograms, optic waveguides with Bragg gratings imprinted in the fiber core, etc. Interference filters belong to the classic optical devices and are well known. Deep holograms have no wide application at present time except holographic optic elements, and are studied for the application in holographic memory devices with high density of recording and storage of information in the volume unit of storage environment. Optical fibers with Bragg gratings wide created and applied in 1992 - 1997 now find their application in sensors, in-line Bragg reflectors, optical amplifiers, filters, laser sources, etc. But on the RC dependence on wave length spectrum we can see side maximums near the main one. Amplitude of these side tops is less than main top. These tops will deteriorate optical characteristics of devices because they become noise sources. Question arises: can we remove or decrease essentially their amplitude? In the theory of filters on the surface acoustic waves where we met the same problem this question was solved by the way of electrodes apodization. It was to be expected that provided apodization of space grating will show the same results. Under space grating apodization we understand that grating amplitude is not stable but changes according to the definite functional dependence along one of the axis.
Development of different branches of industry first of all, and expansion of construction of different kinds of buildings demand accurate measurements in length and angles-improvement of accuracy and reliability of measurement of profiles of complicated configuration. For making engineering and geodesic works more effective modern tools and instruments are needed. An optical distance-meter of a geometrical type used for taking measurements of length in range from 1 - 10 to 500 - 600 m, is also an instrument of that kind. In optical distance meters of geometrical type the measurement of distance is taken by contactless and indirect methods. The base and parallactic angle (gamma) are the fundamental parameters of distance meters of this type. We consider distance meters with a constant base or with a constant parallactic angle. We have constructed a distance meter-profilometer, in which a distance meter of the geometrical type is successfully combined with the method of projection of interference patterns.
A method of impurity laser gettering applicable to complex semiconductors of the CdTe type is suggested and investigated. The methods of photoluminescence and structural analysis revealed the efficiency of laser recrystallization of a semiconductor plate non-operating area which further serves as the getter zone. The mode of laser radiation from the self-absorption area, which leads to priority evaporation of a more volatile component in the complex semiconductor, forms a stable zone of mechanical stresses which in further heat treatment serves as an efficient run-off for undesired impurities and dot defects.
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