Dynamics and spectra of excited states of water-micellar suspensions of single-walled carbon nanotubes

The dynamics of the photoinduced differential absorption and excited-state bleaching spectra of single-walled carbon nanotubes suspended in a micellar solution were studied in the spectral range from 40 to 1000 nm within a time interval from 70 fs to 150 ps under excitation by 50-fs pulses with photon energies 2 and 4 eV. The bleaching and absorption bands were observed in the spectra; the positions of the bleaching peaks were independent of the photon energy of the exciting femtosecond pulse in the range 2–4 eV. It was established that, for delay times shorter than 1 ps, the shape of the differential spectrum of excited nanotubes coincided with the shape of the second derivative of the absorption spectrum of unexcited nanotubes in the frequency range of exciting pulse above 18000 cm^?1 (the range of absorption bands of metallic nanotubes). In the frequency range below 16000 cm^?1 (the range of absorption peaks of semiconducting nanotubes), the bleaching peaks in the differential spectrum of excited nanotubes undergo a high-frequency shift of 200–300 cm^?1 with respect to the second-derivative spectrum of unexcited nanotubes. The excited-state relaxation rate constants were measured. They are well approximated by the exponential dependences and depend on the probe-pulse wavelength. An assumption was made about the nature of the observed spectra of excited nanotubes and about the excitation relaxation.     

Measurement of apex angle of the prism using total internal reflection

Total internal reflection technique is examined critically for the measurement of apex angle of the prism. Recognition of the critical boundary completely specifies the apex angle ‘A’ of the prism by keeping constant the ratio of refractive index of sample fluid (n₁=1.4) to that of glass (n₂=1.7). Recording of observations in the laboratory is dependent upon whether the apex angle ‘A’ of prism is greater than or less than or equal to critical angle ‘r_c’. The minimum value of error function ‘χ’ in the proximity of Abbe angle explain the choice of Abbe type instruments and shown invariant by relating positive ‘₊’ and the negative angle of emergence ‘₋’. Using ray-tracing technique, an expression for the length of the critical boundary ‘l’ is derived and is shown as a measure of the apex angle ‘A’ of the prism.

The choice of the realistic grazing condition leads us to two turning points for which error function ‘χ’ is minimal and yields appropriate option of the measurement of apex angle ‘A’ of the prism. It is further shown that the small error ‘ζ’ crept in the apex angle ‘A’ of the prism can lead to a significant error in the design of Pulfrich type instruments.

Experimental measurements are in-line with the predictions made.     

Effect of the structure of smooth copper surfaces on the accuracy of determination of the optical constants of copper

The accuracy of determination of the optical constants of smooth copper surfaces produced by different technologies is analyzed, with particular attention paid to the consideration of the influence of scattered radiation (which is ignored by many authors) on the retrieval of the optical constants of copper surfaces from reflected radiation. The neglect of scattered radiation can lead to errors as high as 50% in determining the optical constants for bulk copper. For thin films, the errors are much lower. The influence of surface oxidation during measurements in air and surface features of studied objects on the parameters to be determined is analyzed as well. It is shown that errors in determination of the constants are maximal in the plasma resonance region of copper.

     

Nonlinear Amplitude-Phase Effects in Selective Reflection from a Resonance Gas

Selective reflection of a laser wave from a resonance gas is considered for arbitrary intensity, polarization, and angle of incidence on the interface. Variations of the reflection spectra nonlinear in the wave amplitude are studied taking into account the nonlinear increment of the optical phase upon reflection. The result of this increment is a quadrature component of the reflected wave shifted by a quarter period, which may be observed using the homodyning technique (optical mixing). The regularities studied are of interest both for spectroscopy and for nonlinear transformations in the quantum statistics of reflected light.     

Polarization-independent modulation of light in gyrotropic cubic crystals

Polarization-independent modulation of light in gyrotropic cubic crystals is investigated in the Bragg and intermediate diffraction regimes. It is found that, for crystals with considerable specific rotation, the photoelastic anisotropy is suppressed by the circular anisotropy and the observed diffraction efficiency depends weakly on the polarization azimuth of the incident light. Good agreement is obtained between modulation parameters calculated theoretically on the basis of the coupled wave theory and experimental results for a bismuth silicate crystal in the intermediate diffraction regime.     

Selective photorefractive scattering in LiNbO<Subscript>3</Subscript>:Rh crystals

Photorefractive scattering occurs in rhodium-doped lithium niobate crystals irradiated by coherent light. The photorefractive scattering has both wide-angle and selective components. The results of experimental investigation of selective photorefractive scattering in LiNbO₃:Rh crystals and calculation of the spatial structure of scattering are reported. The selective scattering is regarded as a kind of a frequency-degenerate fourwave vector interaction.     

Synthesis of broadband interference filters: II. Suppression of high reflection bands of the fourth,fifth, and sixth orders

The spectral properties of multilayer interference systems formed by multiple replication of the symmetric ternary period ABCBA are investigated. The problem of synthesis of structures with suppression of adjacent bands of high reflection of the fourth, fifth, and sixth orders among their spectral characteristics is solved. It is shown that there are only six variants of selection of the optical thicknesses of layers in a period. When the high reflection bands of the fourth, fifth, and sixth orders are suppressed, the high reflection band of the first order remains in only four cases. The values of refractive indices of layers for which the problem hasa solution are found. The refractive indices of layers in all six cases are described by different relations determining the dependence of the refractive index of one of the components on arbitrarily selected refractive indices of the other two components.     

A comparison of shell theories for large-amplitude vibrations of circular cylindrical shells: Lagrangian approach

Large-amplitude (geometrically non-linear) vibrations of circular cylindrical shells subjected to radial harmonic excitation in the spectral neighbourhood of the lowest resonances are investigated. The Lagrange equations of motion are obtained by an energy approach, retaining damping through Rayleigh's dissipation function. Four different non-linear thin shell theories, namely Donnell's, Sanders-Koiter, Flügge-Lur’e-Byrne and Novozhilov's theories, which neglect rotary inertia and shear deformation, are used to calculate the elastic strain energy. The formulation is also valid for orthotropic and symmetric cross-ply laminated composite shells. The large-amplitude response of perfect and imperfect, simply supported circular cylindrical shells to harmonic excitation in the spectral neighbourhood of the lowest natural frequency is computed for all these shell theories. Numerical responses obtained by using these four non-linear shell theories are also compared to results obtained by using the Donnell's non-linear shallow-shell equation of motion. A validation of calculations by comparison with experimental results is also performed. Both empty and fluid-filled shells are investigated by using a potential fluid model. The effects of radial pressure and axial load are also studied. Boundary conditions for simply supported shells are exactly satisfied. Different expansions involving from 14 to 48 generalized co-ordinates, associated with natural modes of simply supported shells, are used. The non-linear equations of motion are studied by using a code based on an arclength continuation method allowing bifurcation analysis.     

Liquid Ion-Selective Electrodes for Determining Nonionic Surfactants

It was shown that nonionic surfactants (NS) can be determined by potentiometry using liquid NS-selective electrodes. The effect of medium acidity and foreign substances on the operation of liquid NS-selective electrodes was studied. Some properties of NS-selective electrodes were determined.     

Pressure Stabilization Method for Steady Viscous Flows in a System of Pipes

This paper deals with a singular perturbation of the stationary Stokes and Navier-Stokes systems. The term ε²Δp is added to the continuity equation, where ε is a small parameter. For a domain with cylindrical outlets to infinity and exponentially decaying data, existence and uniqueness of solutions under flux conditions at infinity are established for the linear problem and also for the nonlinear problem in the case of small data. Asymptotically exact estimates are proved for ε tending to zero. For sufficiently regular data, these estimates imply the convergence in H _loc ^5/2−δ for the velocity parts and in H _loc ^3/2−δ for the pressure parts, respectively. Bibliography: 17 titles.Dedicated to V. A. Solonnikov on the occasion of his 70th birthday__________Published in Zapiski Nauchnykh Seminarov POMI, Vol. 306, 2003, pp. 107–133.