Possible modifications of the structure of chromophores that have nonlinear optical properties due to the addition of fluorine atoms and fluorine-containing groups to the acceptor site of the molecule are considered. Quantum chemical calculations of dipole moments and first hyperpolarizability were performed for a number of nonlinear chromophores based on N-ethyl-N-(2-hydroxyethyl)-4-phenylazoaniline and modified by the addition of fluorine atoms and fluorine-containing groups to the acceptor site. Positions of maxima in the electron absorption spectrum and the values of Mulliken charges on atoms are also found. It is shown that the addition of fluorine atoms and fluorine-containing groups to the acceptor site of the chromophore molecule leads to a change (increase) in the “efficiency parameter”, defined as the product of the dipole moment by the first hyperpolarizability. The main parameters of a waveguide modulator made of the electrooptical polymer composite with fluorine-containing chromophores embedded in it are estimated.

Possible modifications of chromophore structures with nonlinear optical properties by bonding F atoms and F-containing groups to the acceptor site of the molecules are considered. Quantum chemical calculations of dipole moments and first hyperpolarizability were performed for several nonlinear chromophores based on N-ethyl- N-(2-hydroxyethyl)-4-phenylazoaniline and modified by the addition of F atoms and F-containing groups to the acceptor site. Positions of maxima in the electronic absorption spectrum and the Mulliken charges on the atoms are found. It is shown that addition of F atoms and F-containing groups to the chromophore acceptor site changes (increases) the efficiency parameter, defined as the product of the dipole moment and the first hyperpolarizability. The main parameters of a waveguide modulator made of an electro-optical polymer composite with F-containing chromophores embedded in it are estimated.

Novel amorphous perfluorinated polymers are synthesized and characterized using terahertz (THz) and x-ray spectra. The polymerization of such polymers in which all H atoms are replaced by F is examined. Their optical properties in the THz range show a record low index of refraction for solids in this range. The minimal possible index of refraction for such polymers is estimated. These materials are demonstrated to be highly transparent. The position of a weak absorption maximum in the range 1–2 THz is compared with the characteristic distance between the polymer structural elements that is obtained from an x-ray diffraction analysis of these materials.

Novel amorphous perfluorinated polymers are synthesized and their features are investigated in terahertz and X-ray spectral ranges. We consider the features of the polymerization process for such monomers in which all hydrogen H atoms are replaced by fluorine F atoms. The measurements of their optical features in the THz range show a record low value of the refraction index in comparison with any solid. The possible minimum of the refraction indices for such polymers is estimated. Also the high transparency of these polymers is shown. The X-ray spectra for some of such polymers are measured. The data obtained by X-ray diffraction analysis are compared with the peaks of the terahertz absorption spectrum.

The power dependence α(ν) ∝ ν μ , where μ > 0 is the power exponent which is noninteger in the general case, is observed for amorphous polymers with a small absorption coefficient α in the low-frequency part of the terahertz range, which approximately corresponds to the frequencies ν from 0.1 to 2–3 THz. This dependence is fractal, which is due to the fractal structure of the polymer macromolecules. In this work, we find the power-law index at room temperature for the absorption coefficient of some amorphous polymers. This index is determined on the basis of the dynamics of transmission of a broadband picosecond terahertz pulse through the polymer sample, i.e., using the method of the pulse terahertz spectroscopy in the time-domain representation.

We propose a method for determination of the boundary temperatures of transitions in the structure of polymers by means of analyzing the refractive index of these materials in the terahertz band. The temperatures of glass transition, crystallization, and melting are determined experimentally for isotactic and syndiotactic polypropylenes. Such polymers have low absorption coefficients in the terahertz band. The behavior of intermolecular oscillations of the macromolecules, which are active in polymer spectra in this frequency band, is analyzed.

Terahertz refraction and absorption spectra were measured for isotactic and syndiotactic polypropylene over a frequency range of 0.1-4 THz and for 140-450°K temperatures. Glass transition, crystallization and melting temperatures are clearly pronounced in refraction variation. We try to explain residual absorption of transparent polymers at low THz frequencies.

The basic sizes characterizing the morphology of a few practically important synthetic organic polymers in the glassy and viscoelastic states are confronted with the maxima of the absorption spectra in the terahertz frequency range. These sizes are determined using the X-ray diffraction technique. The absorption spectra of these polymers have been measured by the method of terahertz time-domain spectroscopy in the temperature range from helium to room temperatures.

The optical quality of the eye cornea surface after performing the laser vision correction essentially depends on the characteristic roughness scale (CRS) of the ablated surface, which is mainly determined by the absorption coefficient of the cornea at the laser wavelength. Thus, in the case of using an excimer ArF laser (lambda = 193 nm) the absorption coefficient is equal to 39000 cm(-1), the darkening by the dissociation products takes place, and the depth of the roughness relief can be as large as 0.23 mu m. Under irradiation with the Er : YAG laser (lambda = 2940 nm) the clearing is observed due to the rupture of hydrogen bonds in water, and the relief depth exceeds 1 mm. It is shown that the process of reepithelization that occurs after performing the laser vision correction leads to the improvement of the optical quality of the cornea surface.

For a series of polymers, including crosslinked polymers, based on fluoro-containing acrylic monomers, absorption coefficients are measured in the visible and near-IR ranges. The relationship between the intensities of observed absorption bands and the conversions of monomers during radical photopolymerization is revealed. Absorption bands at 0.85 μm are identified. It is found that the bands centered near 895 and 730 nm correspond to excitations of the fourth and fifth overtones of the stretching vibrations of C-H bonds. The absorption bands centered near 707 and 867 nm are related to the presence of C=C bonds in the monomers.

Absorption spectra of sixteen polymers have been examined using terahertz (THz) time-domain spectroscopy system in THz frequency range (0.1 - 3 THz). All the experimental data showed a characteristic wide absorption peak at the frequencies around 2.5 THz accompanied by smoothly decreasing of refraction (except "transparent" polymers). Such behavior could be described by a modified Debye model. We also tried to clarify the impact of flexibility, polymerization, crystalline degree and number of monomer end groups on polymer dielectric properties. We suggest that the absorption mechanism in spectral range lower than 3 THz is related with relaxation and amorphous state of polymers.

A spectroscopic refractometer is intended for measuring the index of refraction n λ of liquid and solid media at any wavelength λ in a 375–1150 nm wavelength range with an accuracy of ±5 × 10 −5 . It can be used, in particular, for determining n λ of monomers, compositions, and polymers, which are used for creating integrated-optical waveguides operating in a telecommunication spectrum region near 850 nm.

Спектроскопический рефрактометр предназначен для измерения показателя преломления n жидких и твердых сред на любой длине волны в диапазоне от 375 до 1150 нм с точностью ±5 · 10-5. Он может быть использован, в частности, для определения n мономеров, композиций и полимеров, применяемых при создании интегрально-оптических волноводов для телекоммуникационной области спектра вблизи 850 нм.

Like pure water, the water incorporated into cartilage and cornea tissue shows a pronounced dependence of the absorption coefficient on temperature. Alteration of the temperature by radiation with an IR free-electron laser was studied by use of a pulsed photothermal radiometric technique. A computation algorithm was modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The absorption coefficients for several wavelengths within the 2.9- and 6.1-microm water absorption bands have been determined for various laser pulse energies. It is shown that the absorption coefficient for cartilage decreases at temperatures higher than 50 degrees C owing to thermal alterations of water-water and water-biopolymer interactions.

A study is made of the influence of the mass transfer of water on the temperature field occurring in cartilaginous tissue under the action of laser pulses. Two different mechanism of mass transfer of water in cartilaginous tissue (molecular‐diffusion mechanism and laminar flow) have been considered in solving heat‐ and mass‐transfer equations. The calculations have shown that the maximum temperature is attained inside the sample because of the evaporation of water from the biological‐tissue surface. The influence of different parameters of laser radiation and mass transfer of water on the surface temperature, on the maximum value of the temperature, on the position of the temperature maximum, and on the characteristic time at which the diffusion‐limited relaxation of stresses in the cartilaginous tissue occurs has been analyzed.

The effect of temperature dependent shift of water absorption band, known for pure water, has been examined, for the first time, for tissue water, using the IR Free Electron Laser radiation. Cooling kinetics of cartilage and cornea irradiated was measured with a fluorimeter. We have modified the computation algorithm to calculate the optical properties from these measurements more precisely. Temperature dependence of the absorption coefficient of tissue water is studied, for both sides of water absorption bands at 3.0 and 6.1 micrometers . It is shown that cooling kinetics for samples irradiated with small laser intensity is the same, for both wavelengths of each pair: 6.2 and 6.0; 6.35 and 5.92; 3.22 and 2.81; 3.15 and 2.87 micrometers .

We have developed a theoretical model to calculate the temperature field and the spatial distribution of modified cartilage following laser irradiation. The model incorporates both thermal and mass transfer in a tissue with bulk absorption of laser radiation, water evaporation from the surfaces of a slab, and temperature dependence of the diffusion coefficient. We propose that water undergoes a bound-to-free phase transition in cartilage heated to about 70 degrees C and the mobility of proteoglycan units in the cartilage matrix increases. Movement of the proteoglycan units takes place only when the temperature exceeds 70 degrees C and results in tissue denaturation, Using our model, we show: 1) the maximal temperature is reached not on the surface irradiated but rather at some distance below; 2) surface temperature reaches its asymptotic value quicker than the maximal temperature; and 3) the depth of the denatured tissue volume strongly depends on laser fluency, wa wavelength, exposure time, and cartilage thickness. The model allows for the prediction and control of temperature and depth of structural alterations during the course of laser reshaping and treatment of cartilage.

Efficient generation of the fifth harmonic of the radiation from a multimode repetitively pulsed Q-switched Nd:YAP laser was achieved. The total efficiency of conversion of this radiation to the fifth harmonic was ~4% of the energy of the λ=1.0796 μm laser radiation.

A theoretical model is developed for the calculation of the temperature fields and determination of the size of a zone with structural changes in the cartilaginous tissue. The model is based on a simultaneous analysis of the heat and mass transfer processes and it takes into account the bulk absorption of laser radiation by the tissue, surface evaporation of water, and temperature dependences of the diffusion coefficients. It is assumed that under the influence of a phase transition between free and bound water, caused by heating of the cartilage to 70°C, the proteoglycans of the cartilage matrix become mobile and, as a result of such mass transfer, structural changes are induced in the cartilaginous tissue causing relaxation of stresses or denaturation. It is shown that the maximum temperature is then reached not on the irradiated surface but at some distance from it, and that the size of the zones of structural changes (denaturation depth) depends strongly on the energy density of the laser radiation and its wavelength, on the duration of the irradiation, and on the cartilage thickness. This model makes it possible to calculate the temperature fields and the depth of structural changes in laser-induced relaxation of stresses and changes in the shape of the cartilaginous tissue.