Optics and Spectroscopy

Overtone bands in the spectral range of 1300−1920 cm–1 have been found in Raman scattering spectrum of lithium tantalate single crystals. The Raman spectra were recorded in the 180° scattering geometry. The intensity of overtone transitions differs for different samples and, in some cases, is comparable with the Raman scattering intensity at the fundamental modes of a lithium tantalate single crystal.

The influence of energy walk-off in an acoustic beam on the characteristic of anisotropic Bragg diffraction of light has been investigated by the example of paratellurite crystal. The angular and frequency characteristics of acousto-optic diffraction have been calculated in wide ranges of ultrasound frequencies and Bragg angles using the modified Raman-Nath equations. It is shown that the walk-off of an acoustic beam may change (either widen or narrow) significantly the frequency and angular ranges. The calculation results have been experimentally checked on an acousto-optic cell made of 10.5°-cut paratellurite crystal.

The probe field spectrum of a three-level A scheme with a strong standing wave at the adjacent transition is calculated numerically taking into account velocity-varying collisions. It is shown that even a small population of the upper level changes the shape of the spectrum and increases the absorption in the line center. Taking into account the excitation of the level and the saturation of the adjacent transition allows a quantitative explanation of the experiment on argon ions in plasma of a high-current discharge.

The choice of a function approximating the exposure dependence of the amplitude transmission of negative recording media is considered from the standpoint of the theory of measure within the framework of the algebraic model of the system in the geometrical optics approximation. Two processes are taken into account: photodetection in the quasi-linear and the overexposure ranges and light modulation by transparencies made by the method of negative photodetection. Formal construction of the algebra is shown to lead to the approximation by Sugeno negation. Comparison with the approximation by a power polynomial is made.

The absolute values and the shape of the double differential cross section for nonresonance Compton scattering of an X-ray photon by an atomic ion with d symmetry in the core are studied theoretically beyond the impulse approximation for the example of the Ni-like atomic ions Zn2+, Kr8+, and Mo14+. It is established that, as the nuclear charge of an ion increases, (a) in all the scattering channels, the leading harmonics of transition to states of the continuous spectrum are concentrated and (b) the integral intensities of nonresonance Compton scattering are increasingly redistributed to the energy region of resonance Lands-berg-Mandelstam-Raman scattering between the threshold of termination of the Compton profile and the line of elastic (Thomson and Rayleigh) scattering. The calculated results are predictive in character.