Gregory I. Surdutovich

Three polarization reflectometry methods for determination of optical anisotropy.

Three novel methods for the determination of optical anisotropy are proposed and tested. The first, the special points method, may be applied to any uniaxially anisotropic medium and is based on the measurement of s- and p-polarized light reflectances under near-normal or grazing angles (or both) and of the Brewster angle. The second method is based on the use of the Azzam universal relationship between the Fresnel s- and p-reflection coefficients. For a flat surface and an isotropic medium, the Azzam combination of coefficients becomes zero and thus is independent of the incidence angle, whereas for a uniaxial or biaxial anisotropic sample it acquires a certain angular dependence, which may be used to determine the anisotropy of the sample. Finally, for those cases in which the anisotropy of the material of a film deposited on an isotropic substrate is itself of interest, a third method, the interference method, is suggested. This technique makes use of the different dependences of s- and p-polarized beam optical path-length changes on the variation of the angle of incidence.

An interference method for the determination of thin film anisotropy

A new method of determination of thin film anisotropy from the angular dependence of the reflectance interference patterns for s- and p-polarized light is proposed and tested experimentally. The method is based on the different phase angle dependence of polarized light on the incident angle. As a result, the interference patterns of the reflected s- and p-polarized light beams exhibit a different number of oscillations in their angular dependence. The high sensitivity of the method is shown by its application to the interference patterns of a specially prepared multilayer structure with a calculated anisotropy.

Simple reflectometric method for measurement of weakly absorbing films

Abstract Abeles (in E. Wolf (Ed.), Progress in Optics, North-Holland, 1968, p. 251) has shown that the processes of determination of the refractive index and thickness of a transparent film may be completely separated. When under varying incidence angle the relative reflectances of p-polarized light at a film-covered and uncovered substrates surfaces become equal, this means that the angle of incidence coincides with the Brewster angle, θB1, of the ambient–film interface. From a complementary point of view, for a film with non-uniform thickness it is an angle where the interference fringes of all the interference patterns, corresponding to the different film thicknesses, disappear. Moreover, there is yet one angle, θB2, where a samples reflection also ceases to depend on the films thickness and the interference fringes disappear: this is the Brewster angle of the film–substrate interface. Since the reflectances from a growing film or from different places of a tapered film have the same values at these angles θB1 and θB2 the interference patterns should intersect each other at these specific points. For a weak absorptive film the diminution, due to films absorption, of the reflectance at the angle θB1 allows us to determine the extinction coefficient of the film.

Unique Brewster-angle window transparent to both polarizations

Abstract Earlier we proposed a new type of dielectric anisotropic protective coating for Brewster-angle windows (BAW) that retain both the position of the Brewster angle and the true zero of the substrates reflection factor for p-polarized light [1] . The useful property of such coatings consists in the independence of their optical quality from their thickness and this makes them less sensitive to surface damage. On the other hand, by adjusting their thickness one can influence the reflection of the s-polarized light. Here we will show that for any given substrate one can choose a certain value of the horizontal tensor component of the negative anisotropic coating film and then, by adjusting the films thickness, reduce to zero the reflection factor for s-polarized light as well. In the region of positive anisotropy the same optical thickness of a film maximizes the s-polarized light reflectance which may be much greater than that of a clean substrate. Both these variants may be useful under adoption of BAW in resonant laser systems for second and higher harmonic generation.

Combined grazing-angle and normal-incidence reflectometry of absorbing media

We have studied the grazing-incidence differential-reflectance method for obtaining the dielectric function of absorbing media in terms of the derivatives Rp′ and Rs′ of the polarized light reflectances and found that it does not guarantee adequate accuracy for almost any values of the optical parameters. Therefore we modify that approach and describe what we believe is a novel method for the unambiguous determination of the optical constants n and k of a metal and other absorbing materials in terms of the ratio of the derivatives α=Rp′/Rs′ at the grazing incidence and the normal incidence reflection coefficient R. Moreover, it is possible to express α through the logarithmic derivatives (1/R)R′ in the vicinity of the grazing angle. The possibility of performing measurements at the unspecified angle without knowledge of the explicit value of this angle is an evident advantage of this technique. For the great majority of metals and semiconductors the relative errors in the optical constants are comparable to or less than the relative errors in the experimentally measured parameters.

Local fields in meso- and microstructures of two-component media as factors for calculation of linear and nonlinear susceptibilities

Using the generalized method of integral equations we developed the technique for the macroscopic description of any multicomponent medium with allowance of a discreteness of a medium for the first time in molecular optics. Proceeding from the microscopic parameters of the medium we derive the dielectric response and the nonlinear susceptibilities of a two-component crystal.

Optimum solution of transparent and absorbing double-layer antireflection device for electroluminiscent disply and cathode ray tubes

For absorbing coating materials the tasks of attainment of zero reflectivity and optimum transmittance (OT) are not equivalent. On the other hand, for some problems of the communication optics often arises the necessity to achieve OT of already prepared or engineering sample consisting of finite interference-free substrate of the refractive index s overlayered by a film with the preset refractive index t and phase thickness y.

Discreteness and local-field effects in classical molecular optics

We extended the method of integral equations to weakly rarefied media when the distance between the radiators is not negligibly small in comparison with the light wavelength. This enables us to calculate the local fields and the dielectric permittivity of some regular and chaotic media.

Anisotropic protective coating for Brewster angle Windows

We propose what we believe is a new type of dielectric anisotropic coating of arbitrary thickness that can protect Brewster angle windows without degrading their optical quality. Such a coating may be fabricated as a multilayer two-component structure. The parameters of the structure, i.e., the dielectric permittivities of the components and their concentrations, are calculated. For ZnSe windows two examples of anisotropic coatings are presented. The optical quality of the multilayer films does not depend on their precise thickness, which makes them less sensitive to surface damage.

Clustering effects in composite optical materials

The influence of clustering effects on the susceptibility of composite materials is considered by means of a generalized method of integral equations in the case of a two component medium. For the first time the discrete character of the impurities and of the host medium are both taken into account. We have shown that the clustering of the impurities influences the susceptibility of the composite material in all mixtures except for the case when the host medium is a vacuum. The developed approach may be applied to artificial magnetic materials and to photonic band-gap structures in the long wavelength limit.