The frequency of the laser oscillators depends on the optical path length of the resonator, which in turn is influenced both by mechanical perturbations in mirror position and by refractive index variations on the gain medium. Three mechanisms contributing into refractive index changes (temporal and spatial as well) can be distinguished: gas density, electron-plasma density and gain-induced susceptibility.

Over the past decade a revolution has taken place in the methods of short pulse generation from lasers. The development of tunable, solid-state materials has resulted in the appearance of ever more powerful and efficient ultrashort-pulse laser sources. An excellent example is titanium-doped sapphire laser. The advantages of the Ti:sapphire laser over the dye laser are great convenience, more stable operation and tunability. The Ti:sapphire laser can operate with changes of optics to cover the spectral region from 680 nm to 1050 nm, however, dye lasers typically need four different dyes in this region. Ti:sapphire femtosecond laser pulse duration is limited by the group-velocity dispersion (GVD) of the laser cavity with the main contribution coming from the laser rod itself. The GVD of Ti:sapphire crystal is positive throughout its tuning range thus, to minimize the effect one has to include into laser cavity a negative GVD delay line. Several designs based on Brewster cut prisms made out of different materials have been reported so far. In this paper the delay lines consisting of two- and four- prisms sequence, both in double pass configuration are considered. The four-prism sequence is an attractive solution since use of two pairs of prisms made from different materials gives one more control over the dispersive properties of the delay line. We use the method of the ray tracing to estimate wavelength dependent group velocity delay for two- and four-prism sequences. Results of our computer calculations indicate clearly, that a four-prism delay line is superior to that of a two-prism, providing very similar cancellation of third-order dispersion, as two-prism sequence with considerably longer interprism separation.

Secondary spectrum aberrations are especially destructive in high performance refractive optical systems having large apertures and long focal lengths. It is derived that secondary spectrum level of such systems is dependent on a certain structural sum and a deviation of the optical materials used in the system. The structural sum is the main reason of the secondary spectrum aberrations in the achromatic refractive optical systems built with ordinary materials. Reduction of secondary spectrum aberrations is based on the minimization of the structural sum and use of optical material deviation. Essence of the matter is both sign and magnitude of the deviation for the given spectrum direction. A coefficient of secondary spectrum reduction has been introduced. This coefficient receives values in interval from 0 to 1, where value 1 respects the theoretical correction. Medium contributions of this coefficient indicate, whether applied extraordinary optical materials are effective for the secondary spectrum reduction.

Costich's concept of intersection admittance for s- and p-polarization components of reflectivity of symmetrical three-layer subsystems together with depolarization of the incident medium and the substrate is used to design nonpolarizing narrow band anti-reflection coating. First, incident medium with one layer sub-coating and the substrate with three-layer sub- coating which forms a nonpolarizing structure of defined depolarized effective admittances are discussed. Next, the group of three layers was found which operates as depolarized system with effective admittance which match effective admittances of incident medium and the substrates are discussed. Superimposing of all these subsystems arrive at the design of the seven layer narrow band nonpolarizing anti-reflection coating. Ohmer's algorithm in generalized form by Knittl and Houserkova was used for finding the structure of the matching subsystem. Results of calculations are shown in graphical forms using conjugate s- and p- admittance diagrams.

The results to be presented are related to a series of investigations carried out at the Department of Hydrooptics of SOI during a number of years with the aim of development, design and practical employment of optical instruments for measuring the statistical characteristic of turbulent inhomogeneities in the sea water. The values of magnitude and characteristic scales of refractive index fluctuations caused by turbulent convection in the sea water with temperature and salinity stratification, as well as the presence of suspended hydrosol particles, stipulate the choice of devices based on photo-electrical registration of small-angle scattering of light beam propagating through the volume of analyzed medium. The developed modifications of phase-contrast methods (shadow methods) make it possible to detect the variations of light beam angle-of-arrival at the level of 0.03" - 0.05"; the instrument may be mounted on remotely controlled underwater carrier towed by research vessel with the velocity 4 - 12 knots at the desired depth in the range from 0 to 300 m. The interpretation of registered signals from photo-electrical output of the optical instrument is based on the connection between the signal correlation function or spectrum and the energetic spectrum of refractive index fluctuations. The corresponded relations are obtained with the help of the theory of light propagation in random media, namely, the closed equations for light field statistical moments in parabolic approximation. The results of theoretical analysis allows the optimization of optical scheme to meet the requirements of linearity of the signal relation to the analyzed fluctuations magnitude, high spatial resolution and low sensitivity threshold, as well as sufficient resistance to vibrations and changes in pressure and temperature. A measurement of optical fluctuations spectrum in turbulent flow behind a heated grating in hydrodynamic tube are shown to demonstrate the designed instruments abilities. Some results of in-situ experiments made in calm waters and in turbulized layer near thermocline are presented.

The aim of the paper is to compare light scattering models in which the dispersed medium is illuminated by a plane wave (Lorenz-Mie Theory--LMT) and a laser beam (Generalized Lorenz-Mie Theory--GLMT), as well as to discuss the influence of such properties as real and imaginary part of the refractive index of the dispersed phase of the dispersed system on their quality. The quantity discussed is the volume scattering function belonging to the inherent optical properties of the examined medium.

The design principles and the modes of operation of an interference refractometer, made up of standard components of a cube corner interferometer for length measurements, are presented. Equipped with a reference path of rays, the refractive index of air and the displacement of the cube corner reflector may be measured simultaneously. It has been shown, that this system is well suited for absolute measurements of the refractive index of air in high precision metrology.

The modification of the method of refraction measurement of optical radiation is described. The scheme of refractometer which realizes the difference refraction measurement of optical radiation to the moving target is presented.

The measurements problems of polarization parameters of various materials are presented. Detail description of a device designed for polarizatory measurements is given. An anisotropic nonfocal Fabry-Perot interferometer is described. Various aspects of measurement errors are discussed.

A statistically based scheme is proposed to analyze the interference pattern obtained by a spectrophotometric system in order to determine the refractive index and the thickness of the sample. The absolute interference order of the interference pattern is determined with the proposed technique. The major approximation inherent in the method is that the layer must be weakly absorbing and non-dispersive over the wavelength region of interest.

It is shown that distributed feedback (DFB) dye laser may be efficiently employed for measurement of the refractive index of liquid and solid laser materials. Spectral and temperature dependencies of refractive index of dye laser solutions, polymer matrices and micro-porous quartz samples doped with dye are investigated. The change of refractive index of the sample was determined by the wavelength shift of DFB dye laser. A home-made DFB dye lasers with liquid and solid active media tunable in a wide spectral range (400 nm - 760 nm) were used in the experiments.

A laser diode refractive index detector is presented for high performance capillary electrophoresis device. An operational principle of the detector is based on off-axis capillary focusing of the laser beam to the round cross-section capillary and on the detection of interference fringe shifts induced by the refractive index solvent changes in the capillary bore. A principle of an automatic adjustment of the laser diode and a photoreceiver is described for the capillary and solvent replacements. A sensitivity and a linear dynamic range are represented for capillaries with i.d. 0.075 mm, 0.1 mm and o.d. 0.31 mm, 0.17 mm, respectively.

The quantitative description of interferogram registered in heating of crystal which has a finite angle between two surfaces and irradiating of crystal with sounding laser beam is given. The possibility of continuous measurement in real time of crystal's temperature using imperfect interferogram is discussed.

Optical constants of monocrystalline silicon are experimentally determined in the range from 293 K to 700 K using laser lines of 1.06 micrometers and 1.15 micrometers . The quantitative description of spectral and temperature dependencies of the absorption coefficient for indirect optical transitions is given as well as the empirical approximation of spectral and temperature dependencies of refractive index.

The nonlinear M-line technique is based on the analysis of the nonlinear change in the shape of the dark line associated with the excitation of guided waves. It is an easy technique for the determination of Kerr properties of thin films which can constitute optical waveguides. Full spatio-temporal nonlinear modelization tools have been developed recently for nonlinear waveguide couplers which are used for the determination of the complex nonlinear coefficient of new organic materials.

The study of guided waves in a thin layer allows a precise characterization of refractive index and thickness. In our experimental equipment the propagation constants of guided modes were measured by the dark mode spectroscopy technique. Series of dark lines known as the m-lines were observed on the screen. Angles synchronous to the propagating modes were calculated from measurement of the angular distribution of the m-lines. The positions of the m-lines depends on thin film absorption and coupling strength.

A miniature integrated optical refractometer chip based on grating coupling into a gradient effective index waveguide has been demonstrated. The gradient of the effective index resulted from shallow gradients of both the thickness and refractive index of a TiO₂ waveguiding film deposited on a structured fused silica substrate. A method suitable for determining these gradients and data for the wavelengths of 633 nm and 785 nm is presented. Experiments have been performed where the test liquid was used as the cover medium of the waveguide, influencing the position of a laterally confined waveguide mode which represents a convenient on-chip measuring variable. Refractive indices determined by the chip are compared with those obtained by a commercial refractometer. The experimental results show a refractive index resolution of about 2 X 10^-4 for this chip.

Sensitivity of the refractometric sensors on the base of three-layer lightguides was examined in this paper. Characteristic equations for calculation of propagation constant of lightguides with rectangular and circular cross section are used for the determination of influence surfacing films parameters on transducers sensitivity. Experimental investigations confirmed the possibility of transducers sensitivity increase with intensity modulation when using thin surfacing films. Moreover, such structure of sensitive element allows to control the sensitivity of changing wavelength of the light source.

This paper provides a detailed theoretical analysis of the refractive index sensitivity of antiresonant reflecting optical waveguides (ARROW's). The ARROW loss characteristics are determined by the interference effects in the cladding Fabry-Perot cavities and by the reflection phenomena at the interface between the cladding layers. Both mechanisms are described in detail and the significance of each of them is discussed for various waveguide parameters.

In this paper the computer program CADFOS and its prerequisite were described. The program was designed for the purpose of modelling transmission of light in an arbitrary shaped optic fiber path. The program enables us to calculate the attenuation caused by bends of the fiber, the power distribution in any of its cross sections, the power distribution in the near field and far field at the far end of the fiber. Examples of the achieved results have been given.

The subject of this paper is modelling and optimization of fiber optic refractometric sensors that based on the principle of attenuation caused by bends of the optical fiber. Sensors of this type are meant to measure the refractive index of fluids and, after some modifications, to measure temperature. The model designed allows us to optimize the construction of this type of sensors in order to obtain the highest possible sensitivity and linearity of characteristics in the assumed range of changes of the measured refractive index.

Contemporary measurement of several quantities takes out the information signal to have so independent parameters as the number of measured quantities. These quantities (e.g. temperature, pressure, concentration, ...) influence refractive index of the optical fiber or optical channel and the magnitude of light energy in this way. Resolution of single contribution is possible if the measured quantities are linearly independent. Then their resultant operating can be expressed as linearly combination of the all quantities. The signal independent parameters are possible to get with Fourier analysis of the output sensor signal. If the intensity-based sensor is excited with composed periodic signal (with known amplitude and frequency structure) then the change of the optical channel properties is appeared as the change of the amplitude frequency structure. It follows from Fourier analysis that every harmonic component behaves as independent signal and can be used for measurement. Sensor matrix or sensor network matrix is the result as well as calibration matrix.

The new branch of refractometry--refractometry of absorbed substances are discussed. The solving of the inverted problem of reflection refractometry and optimization of measurement condition are described. The principal feature of refractometers for absorbed media are portrait. The special efforts had been expended for the absorbing media metrology creation.

Simple reflection techniques for optical parameter determination of isotropic or anisotropic multilayers on a lower refractive index substrate are presented here. In case of weak absorption in at least one of the layers characteristic minima appear in the angular dependence of the reflectivity by computer fit of which the layer refractive indices and thicknesses can be determined. In case of a monolayer the achieved accuracy is better than the third and fourth decimal in the real and imaginary part of the refraction index, respectively. The fit of bi-layers has lower accuracy, but has the advantage of refractive index determination of non-absorbing layer(s) in the presence of a weakly absorbing auxiliary layer. Comparison between measured refractive indices by reflectometric and optical waveguiding methods shows agreement within 0.001.

The inverse problem of determination of the optical parameters of thin polymer film on the monocrystalline silicon wafer when experimental transmission spectra are used, is solved for the special case of low absorption. Solution is carried out with allowance for the light interference in the film and multiple reflections of light in the wafer. Our results show that dependence of absorption bands intensity on the film thickness is nonmonotonous, i.e. interference has an influence on the optical density of absorption bands in registered spectrum.

Surface electromagnetic waves, known also as surface plasmons (SP), can be achieved if a polarized and collimated light beam undergoes total internal reflection at a glass/metal- film/dielectric interface. The SP phenomenon is observed (recorded) under resonance conditions as a sharp minimum of reflected light intensity (reflectance dip) when the angle of incidence of the laser beam is varied. Possibilities of the applications of this phenomenon to reflectometry of NaCl-water solutions were examined and some experimental results are presented.

The results of the study of photoinduced birefringence processes in different media are reviewed. The application of these results is devices of recording, storing and processing of the optical information and in the phototechnology of making of polarizing optical elements for different function are discussed too.

A novel method of birefringence measurement in highly birefringent elliptical-core and bow- tie fibers influenced by simultaneous action of various stress conditions such as those induced by hydrostatic pressure, longitudinal strain, temperature and twisting effect is presented. The method is based on twist-induced effects in HB fibers and has been successfully applied in a stress environment. The experiments were conducted using a specially designed pressure facility, which made it possible to simultaneously generate several mechanical perturbations, including twist and hydrostatic stress, and to investigate their effects on mode transmission in optical fibers. The results indicate that in the case of HB single-mode bow-tie fibers, hydrostatic pressure and also longitudinal axial strain increased polarization birefringence what closely confirms our birefringence measurement based on Rayleigh scattering.

The theory of elliptic retardation plates that takes into account a phenomenon of multiple reflections is presented. An analytical form of transition matrix for the normally incident plane wave is shown. Sample calculations of phase shift introduced by quartz retardation plates and of the output beam parameters as a function of plate thickness and optical axis orientation were done.

Group-velocity dispersion (GVD) effects, caused by dispersion of optical materials, attracted a great deal of interest in the past decade. Their importance stems from the role they play in generañon and propagation of ultra-short optical pulses. Those effects determine performance characteristics ofultra$ast optical systems by setting limits on the shortest optical pulses that can propagate without significant distortion. We plan to discuss broadening of ultra-short pulses and methods of its compensation in two systems. First we consider mode-locked femtosecond lasers and amplifiers, and then optical fibres.

Refractometry of cryogenic condensed medium is often impeded due to the limited vacuum cavity of cryodines. In our case the measurement of cryodeposit refraction index on the base of optical mirror placed into the vacuum space of cryodine were made. Solving the problem authors [1] used for the measurement of refraction two-beam interferometric method [2 ). They placed the interferometer into the vacuum cryodine space. Athors [3] placed cooling-down mirror in vacuum only. The rest of the device was situated out of cryodine. Moreover cooling-down mirror was placed in such a way that a structure of cryodepositn could not change. It required an arrangement of mirror deeply in the cavity of cryodine, decreasing of window area and a hole at the cryogenic screen. Refraction index measurement method of cryodeposit was developed and experimentally checked by the cryooptics laboratory of S.I.Vavilov Institute and "Engineering-Physical Laboratory" enterprise

Goniometric methods of refractive index determination are most frequently used in practice but they require an application of samples with a prism shape. Interferometric methods use samples with parallel plane surfaces but they usually require the knowledge of samples thickness in advance. The proposed interferometric method has not these shortcomings. It is based on use of Rayleigh interferometer providing sample rotation.

Zscan technique is a powerful method to determine the sign and magnitude of the nonlinear refractive index of optical materials [1]. In this technique the sample is illuminated by a focused Gaussian beam. An aperture is placed between the sample and the detector, and the light transmitted through the aperture is monitored as the sample is moved along the propagation path of the beam through the focal region. The transmittance of another probe beam that is distorted with the refractive index changes caused by the illuminating beam, may be measured as well in the so called two-color extension of this technique [2,3]

Sevralmethods for testthg optical fibers and preforms recently developed by the author [1,2,3,4,5)will be rewieved in this presentation. The first presented method enables measurement of refracitve index profile, residual sUess birefngence, and stress components in axially symmelñcal fiber optic preforms. Dynamic spatial-filtering technique, which is used typically to determine deflection angle $(x) of optical rays passing through the tested preform, was modified to achive bifimctionality of measuring system. Further to a diaphragm rotating in a back focal planeofanobjective imaging the tested preform ( typical configuration of the dynamic spatialltering technique), a modulator of ellipticity is used in a beam iliuminatizg the tested preform which enables measurement ofoptical retardation R(x) introduced by the preform between axially and tiansversally polarized components ofiliuminaling beam. The system may be easily switched (with mechanical switches) from an operating mode enablig measurement of the ray deflection function (x) to an operating mode enablig measurement of the retardation function R(x). Knowing 4(x) and R(x) refractive index profile, residual stress birefringence, and stress components is calculated with the help ofinverse Abel transformation. Examples ofmeasurement results iflustarting the system perfomience are shown. Veiy similar concept is applied to determine refractive index profile, residual siress birefringence, and siress components in optical fibers. In this case, however, wavefront derivative dW(x)/dx (proportional to a ray deflection angle (x)) is directely measured in a scanning-type differentialing interferometcr with a Woliastone prism as a beam splitting element Vciy high Sensitivity requied in this measuring system is achived by applying a sinusoidal modulation of elliplicity of an illuminating beam and a hornodyne detection ofthe first harmonic component ofan output beam. The system can be SWitChed to measuring the retardation R(x) intrOduced by the tested fiber simply by removing the Wollaston prism. As in the pievious case all fiber characterisctics, i.e., refractive index profile, residual stress bireuiingence, and stress components, are obtained by computer pcocessing ofmeasured functions dW(x)/dx and R(x). A method for measuring modla birefringence and polarization mode dispersion in highly birefringent (IIR) fibers is also presented It employs a white.hght interference phenomenon arising between polaiization rriodcs as a results ofinode coupling irduced by pointlike force applied in approximately one halfthe length ofthe tested permits the use of a Wollaston prism without a delay line as an analyzing interferometer. Results of measurements of modal birefringence and polarization mode disperssion at ?826nm are reported for four commercially available fibers: the York Bow-Tie, the Fujikura Panda, the Andrew E-type, and the Andrew D4ype.

Since its introduction by Brunning et al. in 1974, the phase-stepping interferometry has become considered one of the best, quickest and most elegant interferometric techniques. It has found applications in great number of wavefront measuring devices for optical elements control, surface profiling, recognition of shape and deformation, as well as measurement of vibration amplitudes and phases . In this paper some applications of the phase stepping technique in the refractometry of inhomogeneous objects are reported

Two main types of the striped domains in thin layers of chiral nematics can be distinguished: 1 . chiralBloch4ype domain walls placed between two neighbouring homeotropic regions which are indUced in chiral nematic layers by surface interactions ofthe chiral nematic liquid and glass plates; 2. cylindrical myelin filaments freely suspended within homeotropic nematic matrix induced in a chirahnematic thin layer by surface interaction or by an action of external electric (or magnetic) fields. The myelin filaments when oriented perpendicularly to the glass support are visible as the bubble domains and can be hexagonally packed within some regions ofthe layer. The Bloch-type walls have been investigated by T. Akahane and co-workers [1] with the use ofthe differential interference method. The cylindrical chiral myelins are observed at the front of diffusion of the chiral mixture into a homeotropic nematic layer or near the saturation region in the electrically induced phase transition N N. The structure of the myelin filaments has been proposed as a set of coaxial cylinders having the chiral-nematic molecular ordering with radially oriented screw axis [2]. Here, the cylindrical structure of the chiral myelins is confirmed by means of the Pluta fringe-field birefracting niicrointerferometiy. By directly measuring the distribution of the main refractive indices n1 and nas well as their difference n over perpendicular cross-sections of myelin filaments, this technique reveals microscopic features of the molecular arrangement within filaments. Computer models of the molecular structure based on the microinterferometric data are presented.

At present, photonic technologies boost most areas of both communication and sensing. Coincidently, most applications of the novel technical solutions based on any sort of O1)tiCal elements can be found here. Beside of classic bulk optics, there is a rising importance of planar and diffractive optics which is able not only to take many typical tasks of the conventional optics over but also to open guite a few new applications. For the planar and diffractive optics is based on the structures of the size comparable to or smaller then a wavelength, it utilises a modern technology, very the same as a semiconductor microelectronics does. One of the technology noticeably used here is an electron beam lithography which allows to generate the dielectric structures with the lateral accuracy up to 0. 1 micron or even less. Inventioned originally for conductive materials the EBL brings some limitations and peculiarities to the fabrication of the dielectric structures like trapped charge effects, proximity effect and others which will be briefly discussed. Most dielectric structures produced by direct EBL are composed of ultra fine relief patterns created either onto the flat bulk waffer surface or onto the layered sandwitch substrate. The physical methods of microfabricatiou (plasma etching) allow to get the reliefs of the depth comparable to the wavelength of light.

T.he probleni of geometry of puip and probe waves under investigation of nonlinear phctoanisotropy (1ightinthiced birefringence and dichroizi) effects in initially isotropic Ledia are of very importance. However up to now, there are a few papers dedicated to detailed analysis of these questions. 1foreover, a nuniber of peculiarities of registration of effects of anisotropy induced by powerful puLping are unknown yet. This paper solves some of these problem. Using Presnel's operator forsalis (1] we succeeded in estimating of influence of finite quantity of convergence angle between probe and pumping wave normals on registered signal intensity in optically heterodyned polarization spectroscopy and nonlinear polarization spectroscopy schemes. In both cases it is shown that noncollinearity of interacting beams influences on the resonance profile form, though this influence can be rather small. In nonlinear photoanisotropy examination scheme [2) , we are the first to find the polarization conditions for correct interpretation of experimental data. Noticeable violal.ion of Kleinman symmetry for cubic susceptibility tensor components of Pluorescein-doped based acid glass is found. This fact is ecplained by the influence of thermal gratings induced in the medium by nonparallel probe and pumping waves. It is particularly actual in frequency degenerated case. The theoretical analysis of reflection scheme for studying light-S induced anisotropy is also presented. It opens new perspectives under investigation of nonlinear photoanisotropy phenomena.

The refractometry is used for not only technical but biological and medical examinations. Among the letter ophthalmological investigations are predominant. Human eye optical system is examined by refractometry for clinical and research aims. Ergophthalmological investigations are more precise than usual clinical examinations and they are needed in thin technology which is not worked out for the present. Especially such precise and thin measurings of human eye corneal astigmatism are extremely necessary for study of visual capacity and fatigue in all the kinds of visual load work particularly precise visual work and work with display units.