Vladimir S. Gorelik

Angular shaping of fluorescence from synthetic opal-based photonic crystal

Spectral, angular, and temporal distributions of fluorescence as well as specular reflection were investigated for silica-based artificial opals. Periodic arrangement of nanosized silica globules in the opal causes a specific dip in the defect-related fluorescence spectra and a peak in the reflectance spectrum. The spectral position of the dip coincides with the photonic stop band. The latter is dependent on the size of silica globules and the angle of observation. The spectral shape and intensity of defect-related fluorescence can be controlled by variation of detection angle. Fluorescence intensity increases up to two times at the edges of the spectral dip. Partial photobleaching of fluorescence was observed. Photonic origin of the observed effects is discussed.

Raman and fluorescence spectra of fluoro-organic compounds

The results of Raman and fluorescence spectra investigations of fluoroorganic aromatic compounds are presented. We present technique for realizing of qualitative and quantitative analysis of fluoroorganic aromatic compounds on the base of Raman and fluorescence spectroscopy. We propose to applicate the pulsed copper vapor laser for exciting of Raman and fluorescence spectra of fluoroorganic samples. The Raman spectra have been received for a number of compounds as: 1- bromoperfluoroocotane, perfluorodecanoic acid, 1,3,5- trifluoromethylbenzene, hexafluorobenzene, pentafluoropyridine, p-fluoro-DL-phenyl-alanine, m-fluoro-DL- phenyl-alanine, o-fluoro-DL-phenyl-alanine, m-fluoro-DL- tyrosine, 6-fluoro-DL-tryptophan, 5-fluorouracil, 5- Fluorouridine, 5-fluoroindole. On the base of our measurements we have worked out the manner of linear molecule CnF2n+1Br length recognizing. Thus, presented technique, based on using of the modern laser sources and registration system of Raman and fluorescence spectra, permitted to identify the different fluoroorganic molecules in mixtures and pure samples.

Raman scattering in hydrocarbon and fluorocarbon zigzag structures

Raman spectra of hydrocarbon and fluorocarbin zigzag structure molecules are studied. The investigations have been fulfilled for following substances: CnH2n+2 (n equals 6, 7, 10), CnH2nO2 (n equals 4, 5, 8, 10, 11, 13, 15, 18), CnF2n+1Br(n equals 6, 7, 8, 10, 14), for similar structures: H(CF2)10H, H(CF2)10CONH2, F(CF2)5CO2K and commercial products. The frequency shifts of some modes, corresponding to acoustical and optical vibrations, have been observed. The theory, explaining Raman modes frequency dependence on the length of zigzag molecule, is developed. The presence of characteristic isooctane line in Raman spectra of benzines is established. Molecular structure modification of sun- flower-seed oil as a result of technological preparation process has been observed. The obtained results allow detecting zigzag fluorocarbon and hydrocarbon molecules in media and estimating its length with the help of Raman scattering spectroscopy.

Detection of carbon-fluorine bonds in organofluorine compounds by Raman spectroscopy using a copper-vapor laser

The Raman spectra of fluoro-organic compounds show specific emission bands for carbon-fluorine bonds in the range 500- 800 wave numbers (cm-1)). With very limited exceptions, biological materials do not contain carbon- fluorine bonds. Fluoro-organic compounds introduced into biological samples can be detected by a Raman emission signal. Normal mode C-F bond bands are observed: (1) at 710- 785 cm -1 for trifluoromethyl groups; (2) at 530-610 cm -1 for aromatic organofluorine bonds; (3) a range centered at 690 cm -1 for difluoromethylene groups. Specific examples of normal mode C-F bond emissions for organofluorine compounds containing trifluoromethyl groups are: 1-bromoperfluorooctane, 726 cm -1; perfluorodecanoic acid, 730 cm -1; triperfluoropropylamine, 750 cm -1; 1,3,5-tris- (trifluoromethyl)-benzene, 730 cm -1; Fluoxetine (Prozac) commercial powdered pill at 782 cm -1. Compounds containing aromatic C-F bonds are: hexafluorobenzene, 569 cm MIN1; pentafluoropyridine, 589 cm -1. Difluoromethylene groups: perfluorodecalin, 692 cm-1; perfluorocyclohexane, 691 cm -1. Raman spectra were observed with a standard single monochromator. The 510.8 nm light source was a copper-vapor laser operated at 3-10 watts with 10-12 nanosecond pulses at 10 kHz repetition rate. Detection was made with a time-gated photomultiplier tube. Resonance Raman spectra were also observed at 255.4 nm, using a frequency doubling crystal. Observed spectra were free of fluorescence with very sharp strong C-F lines.

Stimulated globular scattering and photonic flame effect : new nonlinear optics phenomena

Novel nonlinear optical phenomena - photonic flame effect (PFE) and stimulated globular scattering (SGS) are discussed.PFE consisted in the appearance of the few seconds duration emission in blue-green spectral range under 20 ns ruby laser pulse excitation and simultaneous excitation of several spatially separated synthetic opal crystalls situated on the Cu plate. SGS was observed both in forward and backward directions. Spectral and energetical SGS characteristics were measured.Novel nonlinear optical effects - photonic flame effect (PFE)1,2 and stimulated globular scattering (SGS)3 - have been discovered. SGS was observed both in forward and backward direction. Pure opal crystal, consisting of the close-packed SiO2 globules with diameter 200 nm, and crystal with pores, filled with molecular liquid, have been studied. Two Stokes components, shifted from the exciting light frequency by 0.4 - 0.6 cm-1, have been observed in SGS. Photonic flame effect consisted in the appearance of the few seconds duration emission in blue-green spectral range under 20 ns ruby laser pulse excitation.

Determination of the length of zigzag chain molecules from Raman spectra

Spectroscopic method of zigzag chain molecules length determination from Raman spectra was developed. The method is based on measuring Raman lines frequencies, corresponding to acoustical modes and different optical modes of chain molecules. The excitation of Raman spectra was produced by continuous argon laser or by pulsed radiation from copper vapor laser.Raman spectra of hydrocarbon and fluorocarbon zigzag structure molecules have been studied. The investigations have been fulfilled for following substances: CnH2n+2 (n equals 6, 7, 10), CnF2n+1Br (n equals 6, 7, 8, 10, 14), CnF2n+2, CnH2nO2 (n equals 4, 5, 8, 10, 11, 13, 15, 18). The frequency dependence of some Raman modes on the length of zigzag molecule has been observed. The theory, explaining this dependence, is developed. The obtained results allow estimating fluorocarbon and hydrocarbon molecules length from the Raman spectra parameters.

Laser detection of toxic substances and microorganisms in water

Spectroscopic method of dangerous substances and microorganisms detection in water is developed. The method is based on analysis of the secondary emission spectra (Raman scattering and fluorescence spectra) of water samples. These spectra were recorded with time delay with respect to exciting light pulse. The excitation was produced by the pulsed ultraviolet radiation from copper vapor laser with non-linear optical crystal cell.

Raman scattering by phonons and polaritons in LiNbO3 and LiTaO3

Spectra of the Raman scattering (RS) by transverse and longitudinal A1-vibrations in crystals of the lithium niobate and lithium tantalate are investigated at room and liquid helium temperatures. An essential decrease of the RS- linewidths for scattering by A1T-phonons is found in the course of deceasing from room to liquid helium temperature. The obtained results show that coherent excitation of polariton modes in ferroelectrics is a promising method for generating the frequency-tunable submillimeter-band radiation.

Raman scattering and anti-Stokes luminescence in wide-gap semiconductors

Raman scattering and anti-Stokes photoluminescence spectra of the crystalline GaP, ZnSe and ZnTe are investigated at room and liquid helium temperatures. The increase of quality-factor of vibrational modes and sharpening of polariton band are found in the Raman spectrum at liquid- helium temperature in a frequency range, corresponding to the TO and LO vibrations. A tentative explanation of the observed anti-Stokes photoluminescence is given with a help of the deep-level state analysis of these materials. The low-temperature anti-Stokes photoluminescence is found to be a common property of the wide gap semiconductors and can probe the spatial distribution profiles of impurities in these crystals.

Raman scattering in crystals of α-sulphur at liquid helium temperatures

Raman scattering (RS) spectra of the crystalline (alpha) - sulphur are investigated at room and liquid helium temperatures. The doublets and quartets are found in the RS- spectrum at helium temperature in a frequency range, corresponding to the intramolecular vibrations. An explanation of the observed splitting is given with a help of the group theory analysis of intramolecular vibrations, affected by the crystalline field. The shifts of the spectral position of characteristic peaks in the RS-spectrum of the (alpha) -sulphur are measured with the temperature variation.