Main research activities
Molecular spectra and structure
Laser diagnostics of thermodynamic and transport parameters of gaseous media
Design and development of tunable IR laser sources, based on nonlinear frequency mixing of laser radiation
Raman and nonlinear Raman spectroscopy of bulk and surface phonon polaritons.
Development of methods and design of equipment for fluorescence diagnostics of early stage malignant tumors
Design and development of unique spectrometric systems
During the last 20 years efficient methods of non-linear spectroscopy have been realized, and new equipment has been developed. Owing to this coherent Raman spectroscopy of gases was developed much further: the spectral resolution and the sensitivity were improved by more than two orders of magnitude. This enable to solve a number of fundamental and applied problems of gas analysis and to acquire new, previously inaccessible information on structure of rovibrational energy states and collisional dynamics of molecules, as well as on intermolecular energy transfer processes.
The unique spectrometer of high spectral (0.001 cm-1) and temporal (10-8 s) resolution, for simultaneous acquisition of spectra of dipole- and Raman-active transitions, was developed. The sources of tunable coherent IR-radiation in the range of 2 - 18 mm, high-precision (10-7) laser radiation spectrum analysers-wavelength meters for the region 0.4 - 1.1 mm were designed. With the help of this equipment Doppler-limited spectral resolution in Raman spectroscopy was realised for the first time, rotational structure of the Q-branch spectra of various classes of molecules was resolved and the peculiarities of this structure, defined by the intramolecular interactions of Fermi- and Coriolis-type were studied.
On the basis of the studies of line broadening in the density range 0.01-100 Amagat, collisional dynamics of molecules has been investigated. High precision of line shape monitoring, observation of Dicke and collisional narrowing effects in CARS spectra under variation of density allowed to distinguish between the contributions of translational, rotational and vibrational relaxation to the line width and shift. Cross-sections of these collisional processes were determined.
Methods were developed of IR or stimulated Raman pulsed selective excitation and CARS probing of the population of rovibrational states, that proved to be efficient for studies of vibrational kinetics in molecular systems. For a number of molecules the rates of vibration-rotation energy exchange have been measured and the peculiarities of these processes, which appear at high levels of excitation into the quasi-continuum state, have been studied. It is worth to note that by means of these methods the rates of collisional vibration-vibration energy exchange of N2 and SF6 molecules were measured, that are the lowest and the highest among all the corresponding values measured for various molecules.
A new technique for production of molecular clusters containing low-volatility materials (such as silicon, fullerenes, silicon nitride and silicon carbide) based on laser-driven reactions in the gas phase and controlled homogeneous synthesis of high purity materials has been proposed and developed. The method is quite promising for nanoelectronic technologies.
Light diffraction from electrostrictive laser-induced gratings (LIGs) has been employed for simultaneous, instantaneous, non-intrusive, and remote measurements of temperature and velocity in a submerged air jet. Phase sensitive detection of the diffracted light was accomplished by superimposing two signal beams whose frequencies are Doppler shifted by the movement of the grating. Temperatures in the range 295-600 K and flow velocities in the range 10-100 m/s were measured in laboratory experiments. Heterodyne detection of electrostrictive LIGs has been applied for characterization of a flow velocities field in cold-gas flows from a subscale thrust-optimized, parabolic rocket nozzle. The experimental results were found to be in a reasonable agreement with CFD calculations, predicting the appearance of a recirculation zone inside the flow at a certain ratio of nozzle and ambient pressures.
The method was proposed and realized of excitation of thermal laser-induced gratings in gases using Raman-active resonances. Study of temporal evolution of LIGs in dense gases was shown to be applicable for coherent spectroscopy of Raman-active transitions and remote non-invasive diagnostics of thermodynamic and transport parameters of gaseous media.
Polariton dispersion and dispersion of the second order nonlinear susceptibilities have been studied in a number of crystals. Fermi-resonance of polaritons with bound and dissociated phonon states has been investigated. Interference of direct and two-step processes in CARS in crystals has been observed and analyzed. CARS from polaritons with spatial separation of the exciting and probe beams has been obtained. Propagation of polaritons was studied.
Large contribution is done into the solution of oncology problems. In co-operation with P.A. Hertzen Moscow Research Oncology Institute the methods and equipment for fluorescent diagnostics of malignant tumors have been developed, that allow early stage cancers to be discovered and localised. Accomplished clinical trials proved their high efficiency.
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