Nonlinear optical parameters and optical limitation in cobalt-doped polyvinylpyrrolidone solutions

Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported.     

System of cryostating wide-aperture nonlinear crystals for generating the fifth harmonic of neodymium-laser radiation

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 5, pp. 867–870, November, 1989.     

Structure of isoregelinone

From a fraction of the bases ofColchicium kesselringii Rgl., growing in the Tashkent Province, a new compound which has been called isoregelinone has been isolated. On the basis of spectral characteristics, especially the INDOR spectrum, and chemical transformations, a structure epimeric with that of regelinone has been proposed for it.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 195–199, March–April, 1981.     

Phytoecdysones ofSilene praemixta. I. Silenosterone

In addition to known ecdysteroids (2-deoxy--ecdysone and 2-deoxyecdysterone) fromSilene praemixta (Caryophyllaceae) we have isolated new ones — premixisterone and selenosterone (I), C₂₇H₄₂O₇, mp 115–117°C (from MeOH), [] _D ²⁸ +86.9 ± 2° (c 0.92, MeOH), yield 0.003%. The acetylation of (I) with (CH₃CO)₂O in Py gave 22-acetyl-selenosterone (II), C₂₉H₄₄O₆, mp 210–212°C (MeOH-C₆H₁₄), [] _D ²⁷ +45.5 ± 3° (c 0.16; MeOH). On the basis of physiocochemical and spectral characteristics it has been established that (I) has the structure of 14,22R,25-trihydroxy-5-cholest-7-ene-3,6-dione. The IR, PMR, and mass spectra of (I) and (II) are presented.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 793–797, November–December, 1979.     

Study of the feasibility of distributed cathodic arc as a plasma source for development of the technology for plasma separation of SNF and radioactive wastes

One of the key problems in the development of plasma separation technology is designing a plasma source which uses condensed spent nuclear fuel (SNF) or nuclear wastes as a raw material. This paper covers the experimental study of the evaporation and ionization of model materials (gadolinium, niobium oxide, and titanium oxide). For these purposes, a vacuum arc with a heated cathode on the studied material was initiated and its parameters in different regimes were studied. During the experiment, the cathode temperature, arc current, arc voltage, and plasma radiation spectra were measured, and also probe measurements were carried out. It was found that the increase in the cathode heating power leads to the decrease in the arc voltage (to 3 V). This fact makes it possible to reduce the electron energy and achieve singly ionized plasma with a high degree of ionization to fulfill one of the requirements for plasma separation of SNF. This finding is supported by the analysis of the plasma radiation spectrum and the results of the probe diagnostics.     

Ion synthesis and optical properties of gold nanoparticles in an Al2O3 matrix

Single-crystal Al₂O₃(0001) and Al₂O₃(1120) substrates are implanted by 160-keV Au⁺ ions with doses from 10¹⁵ to 10¹⁷ cm^?2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al₂O₃. The formation of gold nanoparticles in the Al₂O₃ can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 10¹⁶ cm^?2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n ₂, and the real part of the third-order susceptibility, Rex⁽³⁾, of the composite layers are determined.     

Preparing biodiesel fuel in supercritical fluid conditions with heterogeneous catalysts

Noncatalytic and catalytic transesterification of rape oil were studied in an ethanol medium under supercritical fluid conditions, ultrasonic effect, temperature range from 623 to 653 K, 30 MPa, and with 12: 1 and 18: 1 alcohol to oil mole ratios. An effect of heterogeneous catalysts on the reaction rate was defined. Correlation dependence between the amount of fatty acid ethyl esters in biodiesel fuel and kinematical viscosity of the reaction product was determined.     

Saturated absorption and nonlinear refraction of silicate glasses doped with silver nanoparticles at 532 nm

The nonlinear optical characteristics of silicate glasses doped with silver nanoparticles are investigated by Z-scan technique using second harmonic radiation of picosecond Nd:YAG laser (=532 nm, =55 ps). The real and imaginary parts of third-order nonlinear susceptibility of silver-contained glasses were measured. It was found that the sign of Im ⁽³⁾was negative due to saturated absorption and the sign of Re ⁽³⁾ was changed from negative (self-defocusing) to positive (self-focusing) with growth of laser radiation intensity. The mechanisms responsible for saturated absorption and nonlinear refraction are discussed.