Resonance nonperturbing detector of weak forces in the regenerative regime

The recording of weak classical forces with the help of a resonance optical detector without reciprocal effect is considered. Parametric regeneration of an optical cavity by way of introducing an additional quadratic nonlinear element with illumination at the double frequency is proposed for improving the sensitivity of the system. The limiting sensitivity of such a converter is estimated for a squeezed state of the pumping field and its outlook for practical realization are discussed.     

Change of optimum conditions of second harmonic generation of spatial limited laser beams in nonlinear crystals

Frequency doubling of spatially limited laser beams in nonlinear crystals is investigated theoretically. It was shown that the major factor, which reduces the second harmonic generation (SHG) efficiency in this case, is a diaphragm aperture effect, caused by influence of extraordinary polarized laser beams. In that case a spatial shift of mutually orthogonally polarized beams of the incident waves relative to each other in perpendicular direction of wave transmission at the entry to crystals lead to increase the efficiency of SHG of limited beams.     

Formation of quasi-ordered structures on the surface of strontium titanate in a plasma field

The X-ray diffraction and X-ray spectroscopic properties of strontium titanate single crystals and their surface exposed to plasma have been investigated. Both undoped SrTiO₃ crystals and crystals containing impurity ions of the iron or lanthanum groups have been analyzed. Data on the plasma-induced formation of ordered crystallites on the sample surface were obtained by electron and atomic force microscopy. The crystallites are from 10^?7 to 10^?9 m in size and their hypothetical orientation [321] is independent of the sample orientation and irradiation dose.     

Chaotic generation in a megawatt backward-wave tube

Experimental and theoretical studies on the self-modulation mode of generation in a high-power BWT with the electrodynamic system representing a slightly corrugated waveguide are presented. The BWT is fed by an electron beam with the energy 150 keV and the current 150 A. The system operates at the E ₀₁ mode with the mean frequency 8.7 GHz. Dynamic chaos is obtained by a three-fold increase in the length of the interaction space in comparison with the prototype exhibiting stationary generation. The stationary generation was changed to periodic sinusoidal self-modulation and then to chaotic self-modulation as the current increases from 6 to 60 A. The generation mode is simplified when the current ranges from 70 to 90 A and becomes complicated again for the current exceeding 100 A. Experimental observations are in good agreement with the results of simulation predicting a certain simplification of the self-modulation mode at the currents 70–90 A owing to the effect of high-frequency space charge. Under the conditions of chaotic generation, the mean power was as high as 2 MW at the relative spectral width of the signal 4% and the total duration of the microwave pulse 10 μs.     

Generation of the third harmonic in fullerene-containing polyimide films by picosecond radiation of the Nd: YAG laser

The results of the studies on the transformation of the frequency of laser radiation in polyimide films doped by C₇₀ are presented. The nonlinear susceptibility (χ⁽³⁾) of polyimide 6B films with various concentrations of C₇₀ is studied by third-harmonic generation. At a wavelength of 1064 nm, the value of χ⁽³⁾(−3ω; ω, ω, ω) is 9×10⁻¹³ esu. The effect of the nonlinear variation in the refractive index of the fullerene-containing films on the phase matching between the pumping and third-harmonic waves is analyzed. The third harmonic of the Nd: YAG laser radiation was generated with the efficiencies 6×10⁻⁶ and 10⁻⁶ in the films with the C₇₀ concentration of 0.5 and 0.2%, respectively.     

Strong-interaction approximation in the theory of second harmonic generation of intense short laser pulses

The method of strong interaction of nonlinear waves has been developed to analyse the second harmonic generation of intense laser radiation in the transient regime. Analytic solution for frequency conversion efficiency – taking into account the pump radiation depletion, influence of phase mismatch, dispersion of group velocities and higher nonlinearities – has been first obtained. A comparison of theoretically derived results and known experimental data has been conducted, and a general agreement of these results has been obtained. The optimal conditions of the second harmonic generation of neodymium laser radiation into femtosecond pulse duration range have been determined.     

Crystal Structures of N-[2-(4-oxo-4H-benzo[d] [1, 3]-oxazin-2-yl)benzamide and Propionamide and Their N-Containing Analog N-[2-(4-oxo-3,4-dihydroquinazolin-2-yl)phenyl]propionamide

Crystallography Reports - Specific features of the molecular and crystal structures of two substituted benzoxazinones (I and II) and their structural analog quinazolinone (III) have been analyzed...