Photoluminescence of nucleic bases, DNA, and biological objects

Photoluminescence spectra of nucleic bases, DNA, and two types of microorganisms, excited by the fourth harmonic radiation of the YAG:Nd³⁺ laser with a wavelength of 266 nm, were studied. It was shown that photoluminescence in these biological objects is very efficiently excited due to the closeness of the exciting radiation wavelength to the fundamental absorption edge of an analyzed object.     

The structure and magnetic properties of pyrazolyl-substituted benzimidazole-1-oxyl

The structure and magnetic properties of the benzimidazole-based nitronyl nitroxide radical containing pyrazole as a substituent in its side chain were studied.     

Optics of globular photonic crystals

Recent experimental and theoretical results on the optical properties of globular photonic crystals coauthored by the author are presented. The dispersion relation for electromagnetic waves in a 1D photonic crystal that simulates the properties of a selected direction in the globular photonic crystal is calculated. The spectral ranges that are characterized by the anomalous slowing of electromagnetic waves in the photonic crystal and correspond to the stop-band edges are determined. A method for the measurement of the transmission and reflection spectra of the broadband radiation in photonic crystals is proposed. The method enables one to find the characteristics of the stop bands. The features of the secondary emission that emerges in opals due to the UV and visible excitation are reported. The conditions for the low-threshold lasing in opals filled with rareearth elements are presented. The experimental results on the induced-globular light scattering are demonstrated. Such a scattering implies the coherent excitation of vibrational states of the globules in a globular photonic crystal. A new phenomenon (slow light scattering) which involves the excitation of slow photons (slowtons) that correspond to the stop-band edges of the photonic crystal is observed. The conditions for the measurement of the slow light scattering in opals excited using the ruby and nitrogen lasers are experimentally determined. The experimental and theoretical results open up the prospects for low-threshold nonlinear optical processes in material media.     

Dispersion relation of acoustic waves in phononic crystals filled with dielectric or metal

The results of the theoretical study of acoustic properties of globular phononic crystals based on artificial opals consisting of closely packed SiO₂ globules ∼200 nm in diameter are presented. Dispersion characteristics of the samples under study were calculated, the group velocity and effective mass of phonons were determined.     

Synthesis of anthra[9,1-cd]isothiazolium derivatives and their reactions with nucleophiles

The methylation of 9-methyl-4-methylamino-5H-anthra[1,9,8-bcde]-1,10⁴-dithia-9-azapentalen-5-one takes place at the S₍₁₎, atom and leads to a 2-methyl-7-methylamino-10-methylthio-6-oxo-6H-anthra[9,1-cd]isothiazolium salt, while protonation is directed to the N₍₉₎ atom to give a 5,10-bis(methylamino)-6-oxo-6H-anthra [1,9-cd]dithiolium salt. Depending on their nature, substitution of the hydrogen atom in the 5 or 3 position, reversible addition of a hydroxide ion in the 10b position, demethylation, or opening of the heteroring occurs in the reaction of the anthraisothiazolium cation with nucleophilic reagents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 256–263, February, 1992.     

Electrical manipulation of nanomagnets

We demonstrate that it is possible to manipulate the magnetic coupling between two nanomagnets by means of an ac electric field. In the scheme suggested, the magnetic coupling is mediated by a magnetic particle that is in contact with both nanomagnets via tunnel barriers. The time-dependent electric field is applied so that the height of first one barrier then the other is suppressed in an alternating fashion. We show that the result is a pumping of magnetization from one nanomagnet to the other through the mediating particle. The dynamics of the magnetization of the mediating particle allows the coupling to be switched between being ferromagnetic and being antiferromagnetic.     

Transmission electron microscopy studies of femtosecond laser induced modifications in quartz

Cross-sectional transmission electron microscopy investigations of femtosecond laser induced sub-micrometer structural modifications inside crystalline quartz were carried out. Modifications from single laser shots and from lines built of overlapping shots were imaged. Both single laser shot modifications and line structures show an amorphous core surrounded by a disturbed crystalline structure. A strong strain field surrounding the central, irradiated, core is responsible for an increase of the refractive index. Finite element method calculations of the strain field show maxima on both sides of the irradiated core, which are in good agreement with optical measurements of the refractive-index change. Received: 29 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/947792, E-mail: tatiana.gorelik@rz.uni-jena.de     

Dynamic Opalescence upon Phase Transitions and in Inhomogeneous Systems

The temperature isofrequency dependences of Raman intensities are studied in a number of crystals (lithium tantalate, barium sodium niobate, barium titanate, and quartz) in the low-frequency range near the structural phase-transition points. In the case of ferroelectrics, poly- and single-domain single crystals are studied with a stationary electric field applied to the sample. A drastic increase in the intensity of the quasielastic (low-frequency) light scattering is found when approaching the phase-transition point. The studies are carried out for the 90° scattering geometry as well as at angles close to 180° (backscattering geometry). The anomalies of the quasielastic light scattering near the points of phase transition are observed in the latter case. The position of the maximum intensity of the isofrequency dependence on the temperature scale is found to be dependent on the frequency value = ₀ – (₀ and are the frequency of exciting radiation and the frequency to which the monochromator is tuned, respectively). A theory explaining satisfactorily the observed effect of dynamic opalescence near the phase-transition points in crystals is developed. The specific features of light scattering in an inhomogeneous medium as well as the dynamic properties of the model of such a medium in the form of periodically arranged microresonators are studied. Additional vibrational branches (superlattice vibrations) are shown to be formed in such a medium under certain conditions. These branches give rise to a central peak and strongly affect the characteristics of the structural phase transition depending on the microresonator dimensions. The observing conditions of the dynamic opalescence in inhomogeneous media by the isochronous spectroscopy technique upon pulsed laser excitation are analyzed.