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- Nonlinear Laser Spectroscopy and High-Precision Measurements
- Fundamentals of Laser Chemistry and Biophotonics
Nonlinear Laser Spectroscopy and High-Precision Measurements
Picosecond biharmonic pumping technique in measurements of HTSC energy gap width
Show abstract
We show that experimental data, obtained by picosecond biharmonic pumping technique for high-temperature
superconductive (Y-Ba-Cu-O) films, can be interpreted in terms of non-equilibrium electronic states with a 'frozen'
(meta-stable) energy gap in the electronic spectrum.
Reflection and absorption dynamics in periodic nanostructures based on ZnS/ZnSe
Show abstract
ZnS/ZnSe heterostructures under condition of ZnSe interband excitation by a 150 fs laser pulse exhibit strong narrow-band
modification of absorption and wide-band modification of reflection. Mean decay time for nonlinear reflection in
heterostructures ranges from 2 to 3 ps whereas in bare ZnSe monolayer it exceeds 5 ps. Possible physical processes
responsible for nonlinear refraction in the transparency region include interplay of absorption driven nonlinear refraction
via Kramers-Kronig relations and intrinsic dielectric properties of dense electron-hole plasma. For nonlinear absorption
at ZnSe band edge, interplay of plasma screening effects and states filling effects are relevant.
Transient picometer atomic displacements in a-Te photoexcited by femtosecond laser pulses
Show abstract
Subpicosecond, picometer atomic displacements in &agr;-Te photoexcited by single femtosecond laser pulses have been measured by means of time-resolved optical reflectometry revealing threshold-like coherent quantum emission of single softened fully symmetrical optical A1-phonons and demonstrating absolute detection capability of this technique in studies of coherent phonon dynamics in solids.
Saturation effects and the dip in single-mode laser radiation curve
Show abstract
We show that the dip in the intensity line shape of a single-mode laser can appear at definite experimental
conditions in cases both of nonhomogeneously broadened line as well as homogeneously broadened line of the
atomic transition. In both cases the dip is explained by the nonlinear character of the phenomenon. The
saturation of the population difference of the involved atomic energy levels has its maximum in the vicinity of
the line center. Therefore the saturation of the amplification is at maximum near the atomic line center, and, as a consequence, the lasing power is reduced.
Sub-Doppler spectroscopy based on optical pumping and transit relaxation of atoms in a thin gas cell
Show abstract
The paper is the review of methods, achievements, and possibilities of the recently elaborated and well tested high-resolution
laser spectroscopy based on sub-Doppler absorption and polarization resonances (on centers of quantum
transitions), which arise because of the optical pumping and specific transit relaxation of atoms (molecules) in a thin cell
with a rarefied gas. Theoretical basis of this spectroscopy is presented. Experimental technique and results on the record
of the sub-Doppler spectral structure of Cs and Rb atoms and on the frequency stabilization of diode lasers by given
spectroscopy methods are discussed.
Magnetoelectric Jones spectroscopy of atoms with doublet structure of levels
Show abstract
Theoretical treatment of the magnetoelectric Jones birefringence and dichroism is developed through the bilinear in static
electric and magnetic field dipole-forbidden corrections to the amplitude of Rayleigh scattering. In particular cases of
orientation of the static fields relative the polarization and wave vectors of monochromatic radiation, the amplitude determines
corrections to the refractive index of atomic gas responsible for (i) the Jones birefringence and dichroism, (ii) linear
birefringence and dichroism and (iii) directional anisotropy for the monochromatic wave. The analytical equations and
numerical data for the indicated corrections, calculated for alkali atoms, determine optimal conditions for observing the
effects in vapours. For resonance on D state essential enhancement is discovered in the frequency dependence for the ratio
of refractive index anisotropy of the Jones effect to the square-root product of corresponding anisotropy determining the
Kerr and Cotton-Mouton effects.
Ionization detection scheme for 1s-2s spectroscopy in atomic hydrogen
Show abstract
We purpose a new method for 1s-2s spectroscopy of atomic hydrogen. Our method is based on a new detection
scheme, utilizing a three-photon ionization to obtain a signal correspondent to the excitation of atoms into 2s
state. We report about assembling and test of a proton detection system for this measurement. To measure a
second order Doppler shift we purpose a delayed detection scheme. Using this method we plan to reduce the
uncertainty of the absolute frequency measurement to the 10-15 domain.
Gravitational wave- and radiation pressure-driven dynamics of a Fabry-Perot cavity
Show abstract
We analyze the radiation pressure-induced dynamics of a Fabry-Perot cavity with the movable mirror in the
field of weak plane gravitational wave (GW) with arbitrary reasonable frequency. The obtained response signal
of such GW detector contains mechanical resonant multiplier due to the phenomenon of optical rigidity which
appears in the radiation pressure-driven cavity detuned from resonance. Using the obtained results we study the
possibility of resonant detection of high-frequency GWs.
Laser spectroscopy of hydrogen-bonded complexes of carbazole with water cooled in supersonic jet
N. A Borisevich,
V. A. Povedailo,
E. E. Tselesh,
et al.
Show abstract
Rotational contours of bands of electron and vibronic transitions of the fluorescence excitation spectrum of jet-cooled
carbazole complexes with one, two and three water molecules are studied. For the carbazole-(H2O)1 complex two bands
separated at 0.57 cm-1 are registered at excitation of pure electron transition and other electron and vibronic transitions
by radiation with a spectral width of 0.08 cm-1. This is caused by the tunnel effect. The intensities of the shifted low-frequency
bands are three times as weak as the high-frequency ones because of different nuclear spin-statistical weights.
Water molecules in carbazole-(H2O)2 and carbazole-(H2O)3 complexes are combined into a chain by the hydrogen bond.
Both ends of this chain are also hydrogen-bonded with a carbazole molecule. There is the interchange of the axes IA and
IB of the principal moments of inertia in the carbazole-(H2O)3 complex, as compared to the remaining considered complexes.
This results in increasing the Q-branch intensity.
The research of precursors of parametric instability in Fabry-Perot interferometer
Show abstract
The basis of undesirable e.ect of parametric oscillatory instability in Fabry-Perot cavity is excitation of the
additional (Stokes) optical mode having frequency ω1, and the mirror elastic mode, having frequency ωm. It
appears when optical energy stored in the main mode, with frequency ω0, exceeds a certain threshold and the
frequencies are related as ω1 approximately equal to ω0 - ωm. The presence of anti-Stokes with frequency ω2 approximately equal to ω0 + ωm may depress parametric instability. We analyze the time evolution of parametric instability with account of both
Stokes and anti-Stokes mode. It allows predicting the characteristics of precursors of parametric instability. Observation of such precursors may help to avoid parametric instability.
Spatial thermal inhomogeneities as a source of Brownian motion
Show abstract
Experimental investigations of the thermal diffusion motion of individual probe microparticles in various liquids have
been carried out by using the phase-sensitive laser method of light-scattering spectroscopy. It has been shown that at
observation times τ ≥ 1s there is a good agreement between the obtained experimental data and the well-known Einstein-Smoluchowski linear law of Brownian motion (see manuscript for equation). At small observation times τ<<1 s, the square law of motion (see manuscript for equation) is valid. The molecular cooperative mechanism of action of the liquid on a microparticle
as a result of relaxation of thermal spatial inhomogeneities is discussed.
Room-temperature magnesium vapor cell for spectroscopy on the 1S0-3P1 intercombination line
Show abstract
A new type of compact magnesium cell with room-temperature walls have been developed for high resolution
spectroscopy on the Mg 1S0-3P1 intercombination line. Saturation resonances with a FWHM of 1.3.MHz have been
detected in this cell in the fluorescence signal. The time selection method was applied to eliminate the background signal
caused by the scattering of laser beams on cell windows. The signal-to-background ratio drastically increased by the
spatial localization of excited atoms owing to collisions with atoms of a low-pressure inert gas.
New Doppler-free resonance in field of counterpropagating waves
Denis V. Brazhnikov,
Alexey V. Taichenachev,
Anatoliy M. Tumaikin,
et al.
Show abstract
The resonance of saturated absorption in counterpropagating light fields is experimentally and theoretically studied. We
focus on two cases: parallel and linearly polarized waves, driving an open dipole transition and the general case of
elliptically polarized waves, driving closed dipole transition. The former reveals a new Doppler-free resonance as a peak
within the saturated-absorption dip. The latter case reveals a new polarization effect, causing a shift and asymmetry of
the saturated-absorption resonance. The results obtained can be found useful in metrology.
Effects of saturation and self-saturation in a field of opposite spreading laser waves on transition J=1-J=1
Show abstract
The form of the saturated absorption resonance for atomic transition J=1-J=1 at arbitrary intensities of a probe light field
is calculated. The influence of the saturation effect of optical transitions by own spontaneous radiation on the form of a
nonlinear resonance is researched. It is revealed, that in case of orthogonal polarizations of strong and probe fields the
increase of the probe field intensity can result in inversion of the shape of a nonlinear resonance. The saturation effect of
optical transitions by own spontaneous radiation increases contrast of the inverted resonance of saturation and narrows
its spectrum. In case of parallel polarizations of optical fields the peak of absorption can arise in the shape of nonlinear
resonance at splitting of the lower atomic state.
Parametric instability in GEO 600 interferometer
Show abstract
We present the analysis of undesirable effect of parametric instability in the signal recycled
GEO 600 interferometer. This effect leads to the excitation of the additional (Stokes) optical mode,
having frequency &ohgr;1, and the mirror elastic mode, having frequency &ohgr;m. This happens when the
optical energy stored in the main interferometer mode, having frequency &ohgr;0, exceeds a certain
threshold and the detuning &Dgr; = &ohgr;0 - &ohgr;1 - &ohgr;m is small. We discuss the potential of observing the effect of parametric instability and its precursors in GEO 600 interferometer. This approach provides the best option to get familiar with this phenomenon, to develop experimental methods to depress it and to test the effectiveness of these methods in situ.
Definition of the ABTS-test efficiency by Raman spectroscopy method
Show abstract
Dynamics of the biochemical reactions of the ABTS-test had been investigated by the Raman spectroscopy method for
the first time in this work. Velocity coefficients of the given reactions and the theoretical model of the ABTS-test reactions
had been specified by the experiment.
Single frequency linearly polarized DFB fiber laser source
Show abstract
A distributed feedback fiber laser formed in non-polarization maintained ytterbium doped fiber has been studied, its parameters
have been measured in dependence on pump power and pump wavelength. Laser performance has been compared for
two regimes of fiber heat sinking. Under conditions of sufficient acoustical insulation no polarization mode competition
have been observed thus single polarization can be achieved with external polarizer.
Coherent radiation in 3-level V-system with strong bi-harmonic driving field on adjacent transition
Show abstract
Coherent radiation of 3-level dense medium with strong polyharmonic driving field on adjacent transition has been
researched by numerical solving of density matrix equations together with Maxwell equations. The polarization spectrum
consists of coherent peaks on the frequencies separated from probe field frequency by modulation (beat) frequencies and
its harmonics.
Formation of narrow optical resonance by micrometer thin Rb-vapor layer
Show abstract
Recently developed thin cells containing atomic vapor of micrometric column thickness L allow one to study
peculiarities of Electromagnetically Induced Transparency (EIT) phenomenon, along with the accompanying velocity
selective optical pumping/saturation (VSOP) resonances for the case when < 100 &mgr;m. The micrometric thin cells (MTC)
are filled with pure Rb and neither buffer gas nor paraffin-coated walls were used. The Λ-systems on D2 line of 85Rb
have been studied experimentally with the use of bi-chromatic radiation of two separate diode lasers (λ≈780 nm, γL&≈ 5MHz). It is demonstrated that when L~60 &mgr;m it is still possible to form the EIT resonance with the sub-natural
linewidth ~ 5 MHz. The EIT resonance linewidth increases up to 10 MHz , when column thickness L is reduced down to
~ 2 &mgr;m. Six VSOP resonances are detected in the fluorescence and absorption spectra when the thickness L ~ 10 &mgr;m.
Dependence of the EIT resonance linewidth as a function of the atomic vapor column thickness L is presented.
Two-photon absorption and laser photochemical decomposition of trans-stilbene substitutes
Show abstract
The two-photon absorption (TPA) cross section of an ethanol solution of of three molecules (a trans-stilbene and its
derivatives) exposed to radiation of the second harmonic of a Nd:YAG laser (532 nm) of nanosecond duration has been
determined using the method based on the measurement of the photochemical decomposition of examined molecules,
characterized by a low photostability. The quantum yield of the photoreaction (γ266) of dyes under one-photon excitation (4-th harmonic Nd-YAG laser 266 nm) was preliminary determined by absorption method. Then photochemical
decomposition of molecules was investigated at two-photon excitation TPA cross-section was determined. At definition
of TPA cross-section of molecules, influence transient S1-Sn absorption was taken into account. Comparison of values of
TPA cross-section determined in the work, with the experimental and theoretical data received by other authors for these molecules were carried out.
Highly effective method for temporal terahertz spectroscopy under the condition of random probe signals
Show abstract
As it is well known, terahertz time-domain spectroscopy is very perspective method for identification of molecules. The
main difficulty of its application, on our opinion, is an absent of high effective method for temporal analysis of the medium
response spectrum. According to [13] methods, using in time-domain spectroscopy for treatment of experimental
results, have some bad features, which lead to absurd results sometimes. In [14,15,20,21] we developed two possible
ways to create effective algorithms for the analysis of instantaneous spectral intensities of medium responce under the e
action of pulse with a few cycles. It should be stressed that in the first algorithm we used the Gabor-Fourier window
transform, investigated its efficiency and formulated requirements to its parameters for reconstruction of spectral dynamics
of medium response with high quality. The second algorithm, based on application of SVD method, allows to obtain
an information about many spectral lines simultaneously from one series of measurements of medium response characteristics.
In both algorithms, their parameters were ideal ones without any random fluctuations. This paper deals with the
more realistic situation: we investigate possibility to get dynamics of any spectral lines of medium response when parameters
of measurements are random. Our investigation demonstrates the high efficiency of using method based on
SVD algorithm. We apply it as for ideal medium response constructed on the base of some ideal oscillators, as for results
of physical experiments. Also below the new approach to finding of instantaneous spectral amplitudes for requiring frequencies
under the action of terahertz pulse is proposed. It allows to investigate a frequency dynamics due to using of integral
measurements of optical signal.
Laser spectroscopy of atoms approaching a surface of ionic crystalline material: evidence of pure dephasing due to stochastic near fields
Show abstract
The shape of the luminescence spectrum of Cs atoms flying near a sapphire surface is explored experimentally and described phenomenologically for the detuning range of 5 to 50 cm-1 on both sides of D2 line. The numerical fitting of one theoretical parameter and a small variation of another parameter ensure a satisfactory agreement with the experimental spectrum. The experimentally determined abnormally high intensity of the antistatic wing is explained by the effect of phase relaxation of the atomic transition, caused by fluctuations of the electric field of oscillating ions of the sapphire crystal lattice.
CARS investigation of collisional broadening of the hydrogen Q-branch transitions by water at high temperatures
Show abstract
By means CARS interferometric lineshape spectroscopy the temperature dependences of broadening coefficients for
several Q-branch transitions of hydrogen molecules under collisions with water molecules were determined at
temperature range 2100
The possibility of single-shot high-resolution CARS lineshape spectroscopy
Show abstract
Influence of a random nature of light on a possibility of realization of single-shot high-resolution lineshape spectroscopy
is discussed. Non-linear interaction of light with matter in CARS process could change initial light statistics. Broad band
CARS with use of conventional dye lasers as a source of Stokes waves conserves the initial <<exponential>> light statistics
peculiar to broadband radiation with modes structure. Dual Broad Band CARS-approach can change light statistics from
<<exponential>> in Stokes wave to <<normal>> in anti-Stokes radiation providing the possibility to realize the single-shot high-resolution lineshape spectroscopy.
Single shot CARS thermometry of hydrogen-contaning multicomponent gaseous mixtures at high pressure and high temperature
Show abstract
We demonstrate the feasibility of the proposed new approach to CARS thermometry of hydrogen-containing mixtures
with simultaneous measurement of the intensities of a hydrogen spectrum Q-branch lines and their linewidths in a single
laser shot by means of a spectrograph combined with an interferometer, that have orthogonal directions of dispersions.
This provides correct temperature evaluation that takes into account the linewidths, measured directly. The experiments
were carried out in a H2:N2 = 1:10 mixture in a heated cell at a temperature of 1050 K. The values of gas mixture
temperature, that were defined in a pressure range of 2-9 MPa from DBB CARS spectra taking into account linewidth
corrections, coincide with a thermocouple measurements within ~ 2 %. Without these corrections the discrepancies
increase up to 5 %. The proposed approach can be applied to CARS thermometry in the course of investigations of H2
and hydrocarbon combustion without the necessity to measure species concentrations, and does not require the
knowledge of the line-broadening coefficients.
Simulation of random lasing under diffusive regime of radiation propagation
Show abstract
Monte-Carlo simulation of random lasing under diffusive regime of light propagation in active random medium was
carried out. Computing has been carried out for active media being suspension of dielectric particles in rhodamine 6G
solution. Dependence of emitted photons density distribution in active media, their total quantity and spectrum on active
medium length in a pump beam direction. Spatial distributions of pump radiation and amplification in a sample have
been taken into account. It has been shown that quantity of emitted photons non-steadily depends on sample length and
the maximal density of emitted photons is located at a depth near front (pump) sample side. Optimal active medium
length is exists and maximizes total number of emitted photons and narrows spectrum of emission. Computing results
are conformed to experiments.
Frequency bistability in nonlinear thin-film interferometer
Show abstract
The bistability in a thin-film cavity system including a layer with the quasi-resonant polarization is considered.
Bistability in reflection frequency dependence and arising phase drift can be applicable for creation of chirping mirrors
for laser pulses transformation.
Fundamentals of Laser Chemistry and Biophotonics
Ultrafast x-ray spectroscopy for structural dynamics studies in chemistry and biology
Show abstract
Time-resolved x-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resolution is a
new method to observe electronic and geometric structures of short-lived reaction intermediates. It combines an intense
femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light
Source (SLS). We present key experiments on charge transfer reactions as well as spin-crossover processes in
coordination chemistry compounds next to solvation dynamics studies of photogenerated atomic radicals.
Femtosecond polarisation spectroscopy of the vector correlations in the photodissociation of polyatomic molecules
Show abstract
In order to adequately describe rotation of photofragments and dynamics of vector correlations in liquids, we have
generalized the J-diffusion model by allowing the rotational relaxation rate to be angular momentum dependent.
The calculated nonequilibrium rotational correlation functions (CFs) are shown to decay much slower than their
equilibrium counterparts, and orientational CFs of hot photofragments exhibit coherent behavior, which persists
for several rotational periods. In practical terms, the standard and generalized J-diffusion models are shown
to be almost indistinguishable under equilibrium conditions. Far from equilibrium, their predictions may differ dramatically.
Conception of hystons in bacterial photosynthesis: spectra, exciton dynamics, and electron transfer
Vladimir S. Pavlovich
Show abstract
It has been shown that among the great diversity of available vibrational modes there are two types so called hμ- and hα-
hyston modes in the light-harvesting (LH) antennas and in the complexes of the reaction centers (RCs), which produce
high modulated broadening of excitonic spectra with radically different temperature behavior. At the same time the hμ-
and hα-modes initiate different activationless electron transfer (ET) processes in the RCs. Novel formulas is presented,
which making it possible to describe known experimental data on the half-width of the B800, B850 absorption for LH2
antennas and the P870 and P960 absorption for RCs as well as on the temperature effect on the ET rate. The primary ET
is considered as a resonant nonradiative transition between P* and P+BA- states with next stabilization (P is a special
pair, BA is an accessory bacteriochlorophyll in A-branch of RC). It has been shown that the hα-mode with own frequency
in the range of 130-150 cm-1 controls the primary ET from P* to bacteriopheophytin (HA).The ET matrix elements are of
12.7 ± 0.9 and 12.0 ± 1.2 cm-1 for Rps. viridis and Rb. sphaeroides respectively. An oscillation mechanism is discussed
for ET from P* to BA and then to HA. It is assumed that water fulfils the transmission function in the primary ET. It is
obtained that the hμ-mode of 304 cm-1 governs the secondary ET from HA to ubiquinone in Rb. sphaeroides RC.
Ultrafast photoprocesses in contact ion pairs of indotricarbocyanine dyes
Show abstract
The paper presents recent experimental results on the peculiarities of fluorescence and transient absorption exhibited by indotricarbocyanine dyes in solutions of different nature. The dynamics of transient absorption spectra of the molecules under study is analyzed within the framework of the concept of intra- and intermolecular vibrational relaxation and ultrafast charge transfer in contact ion pairs.
Delta-ALA-mediated fluorescence spectroscopy of gastrointestinal tumors: comparison of in vivo and in vitro results
Show abstract
The limitations of standard endoscopy for detection of dysplastic changes of mucosa are significant challenge and
initiate development of new photodiagnostic techniques, additional to diagnostic possibilities of standard endoscopic
equipment. One of the most widely examined optical modalities is the laser- or light-induced fluorescence spectroscopy
(LIFS), because of its rapid and highly sensitive response to early biochemical and morphological changes in biological
tissues. In the recent study delta-aminolevulinic acid/protoporphyrin IX is used as fluorescent marker for dysplasia and
tumor detection in esophagus and stomach. The &dgr; -ALA is administered per os six hours before measurements at dose
20mg/kg weight. High-power light-emitting diode at 405 nm is used as an excitation source. Special opto-mechanical
device is built to use the light guide of standard video-endoscopic system. Through endoscopic instrumental channel a
fiber is applied to return information about fluorescence to microspectrometer. The fluorescence detected from in vivo
tumor sites has very complex spectral origins. It consists of autofluorescence, fluorescence from exogenous
fluorophores and re-absorption from the chromophores accumulated in the tissue investigated. Mucosa autofluorescence
lies at 450-600 nm region. The fluorescence of PpIX is clearly pronounced at the 630-710 nm region. Deep minima in
the tumor fluorescence signals are observed in the region 540-575 nm, related to hemoglobin re-absorption. Such high
hemoglobin content is an indication of the tumors vascularization and it is clearly pronounced in all dysplastic and
tumor sites investigated. After formalin conservation for in vitro samples hemoglobin absorption is strongly reduced
that increases mucous fluorescence signal in green-yellow spectral region. Simultaneously the maxima at 635 nm and
720 nm are reduced.
Photo catalytic isotopes separation
Show abstract
New materials with prescribed isotopic composition could open good possibilities of functional characteristics
needed for the progress in science and technology. [1]. It have been shown, that the thermal conductivity of the
monocrystallic 70Ge (99,99 %) at 15 K was as much as 8.1 higher than the corresponding parameter of the natural
isotopic structure [2]. Applications of the single isotopes compositions are restricted by their high cost. That's why
it is very promising to find out new and less expensive methods of isotope separation and characterization of new
materials [1].
Terahertz radiation influence on peptide conformation
Show abstract
Terahertz radiation affects on peptide optical properties and decreases a binding capacity of protein with native ligand. This indicates that terahertz radiation induces changes in peptide conformation.
Selective photodestruction of chiral molecules of a specified configuration by coherent laser radiation
Show abstract
The method of selective destruction of small chiral molecules of a specified configuration, which is based on
coherent action of the intense multicomponent ps and fs laser pulses, is suggested. Computer simulation results
show its efficiency for the laser distillation of a racemic mixture of randomly oriented molecules in a gas phase
at room temperature.
Photodynamics of pyrene-flavin and phenothiazine-flavin dyads
Show abstract
A pyrene-flavin (isoalloxazine) dyad (PFD) and a phenothiazine-phenylene-isoalloxazine dyad (PPF), dissolved in
dichloromethane are characterized by absorption and emission spectroscopy. These dyads are model compounds for
flavin based blue-light photoreceptors. Absorption cross-section spectra, fluorescence quantum distributions,
fluorescence quantum yields, and fluorescence decay times are determined. The absorption spectra of the dyads
resemble the superposition of the absorption spectra of the constituents (1-methylpyrene, isoalloxazine, and
phenylphenothiazine). Photo-excitation of the flavin moiety causes fluorescence quenching by reductive electron
transfer in thermodynamic equilibrium with the exited flavin subunit. The charge-separated states recover by charge
recombination. Photo-excitation of the pyrene or phenylphenothiazine moiety causes oxidative electron transfer with
successive recombination, and additionally Förster-type energy transfer and Dexter-type energy transfer. For PFD in
dichloromethane the rates of reductive electron transfer and oxidative electron transfer were determined to be (5 ps)-1
and (77 ps)-1, respectively, and a charge recombination time of about 16 ps was found. For PPF in dichloromethane the
rates of reductive electron transfer and oxidative electron transfer were determined to be (700 fs)-1 and (100 ps)-1,
respectively. The HOMO level position of the pyrene radical cation subunit relative to the HOMO level of the excited
isoalloxazine subunit is determined from the delayed fluorescence emission of the PFD sample.
Multiple-scattering Henyey-Greenstein phase function and fast path-integration
Show abstract
It is shown that stability of Henyey-Greenstein phase function gives a possibility to solve quickly a multiple-scattering
light propagation problem with the same a priori information about interaction as in the primary problem definition.
Conformation change of enzyme molecules in laser radiation field
Show abstract
As a result of an analysis of macromolecules properties in the coherent optical radiation field and with allowance for the
experimentally obtained unique data on the interaction of lazer radiation with biomolecules (dependence of the
interaction efficiency on the coherence length, presence of the effect in the spectra region far from the absorption band),
a mechanism of wave interaction is developed. Using this mathematical model, the calculations of a change in the
macromolecules oscillatory energy in the coherent radiation field are performed. It is shown that the increase of
macromolecules oscillatory energy depends strongly on the coherence length of radiation. On exposure to noncoherent
radiation, the biomolecules oscillatory energy practically does not change, whereas on exposure to laser radiation
(coherence length ≈3 cm), energy of oscillations of atoms increases by an order of 2÷4, which results in a change in the
conformation of biomolecules and activity of enzymes. Recently a lot of data are received concerning the change of lysosomal enzymes activity in blood plasma under action of laser radiation.
Fluorescence from upper excited states of porphyrins with one- and two-photon excitation
Show abstract
In this paper we report on the study of S2→S0 blue fluorescence and two-photon absorption (TPA) for a series of Zn-tetrabenzoporphyrins
(Zn-TBP) with sequential substitution of phenyl groups in meso-positions. The blue fluorescence
has been measured with both one- and two-photon excitation. The data on TPA showed that lowest g-parity state lies
above B-state for all these compounds and blue fluorescence has been detected upon two-photon excitagtion at g→g
transition energies above that of Soret band. The data are in line with the suggested role of the g-parity low-lying state in
the nonradiative deactivation of B state. More than two-fold decrease in the relative yield of blue fluorescence was found
in going from Zn-monophenyl-TBP to Zn-tetraphenyl-TBP. The enhancement of the radiationless internal S2→S1 and
S1→S0 conversion and the decrease in the quantum yield of blue fluorescence was proposed to explain by nonplanar distortions of tetrapyrrolic macrocycle in Zn-tetraphenyl-TBP. The obtained results indicate that the positioning of g-parity excited states above B states is a requirement but not the sufficient condition for presence of blue fluorescence.
Local field enhancement for silver and palladium clusters photodeposited on TiO2 nanocrystals
Show abstract
Field enhancement coefficient was calculated for silver and palladium clusters photodeposited on titan dioxide
nanoparticle. It was shown that experimental fluorescence enhancement can qualitatively be explained by plasmon
resonance and nanosystem geometry.
Photophysical properties of photosensitizer chlorin e6 incorporated into polyvinylpyrrolidone
Show abstract
It has been demonstrated that chlorin e6 form molecular complex with polyvinylpyrrolidone. The binding constant and
the number of binding sites have been determined as Κ= (2.5 ± 0.5)•104 M-1 and N = 2.1 ± 0.5, respectively. Complex in comparison with free chlorin e6 possesses increased fluorescence quantum yield, triplet and singlet state lifetimes, slightly modified intersystem crossing quantum yield, and also more intensive and red shifted absorption band locating in the "phototherapeutic window" of biological tissues. The photophysical properties of chlorin e6 incorporated into the polymer are insensitive to pH. The formation of the complex leads to the disruption of chlorin e6 aggregates at acidic pH.
Binding to polymer only slightly improves photophysical properties of photosensitizer and should not provoke fundamental changes in PDT efficiency.
EMF measurements across the front of combustion wave during layer by layer surface laser sintering of exothermal powder compositions
Show abstract
Rapid prototyping (RP) and manufacturing (M) is a novel layer-by-layer fabrication technique which has become
increasingly popular due to its inherent flexibility for the manufacture of simple and complex 3D parts. Early we had
been shown opportunity of selective laser sintering (SLS) of different type powder systems (intermetallics, ceramics,
ferrites, high-temperature superconductors), traditional use for self-propagated high-temperature synthesis (SHS). The
non-thermal heating affect of an external electromagnetic field during SHS is related to the specific system under study
due to differences in movement of defects and ions at the 'plasma-like' molten combustion wave front. We have
developed and refined the testing scheme for electro-thermal phenomena studies which can directly influence on the SHS
combustion wave front. This work studies electromotive force (EMF) measurements across the front of combustion wave
during layer by layer surface laser sintering of exothermal powder compositions (Ni-Ti, Ni-Al). Analysis using an
analog-digital-analog computer converter allowed some control of the laser movement and hence some control of the
exothermal reaction - in so doing it provided near optimum conditions for forming layered 3D articles. Comparative
results of structural-phase transformation during laser control SHS in reaction-capable compositions are presented.
Study of photoreduction kinetics of xanthene dyes with intersystem crossing from upper triplet states
Show abstract
Modeling of kinetics of photoprocesses in polyatomic molecules based on four-level energy scheme is carried out. The
model includes the processes in dye under cw photoexcitation and takes into account a reverse intersystem crossing and
photochemical reaction from the upper triplet states. The analytical time-dependent relation for dye concentration of the
initial form was obtained taking into account the contrast of rates of various photoprocesses and using of quasistationary
approximation. It was shown that rate constant of photolysis correlates with probability of intersystem crossing of the
dyes. For the xanthene dyes in gelatin it was shown that simple experimental method of cw laser photolysis combined
with the kinetic model could be effective technique of study of upper excited states participation.
Phosphorescence study of matrix effect on Pd-porphin macrocycle conformation
Show abstract
In this paper we report the spectral manifestation of existence two spectral forms of Pd-porphin in wide set of Shpol'skii
matrices at cryogenic temperatures. The short-wavelength spectral form is attributed to the structure, where the central
Pd(II) ion is in plane of the porphyrin macrocycle, while the long-wavelength form is associated with the nonplanar
saddle-type conformation of the PdP. The frequencies of the normal vibrations in the ground electronic state have been
measured separately for both forms and the differences in the normal modes of two macrocycle conformations are
discussed. The type of molecule distortion has been established with using information about the frequencies of vibronic
modes from high-resolved spectra of metalloporphins. Matrix effect was shown to have significant role in the stabilization of each of two conformations.
Spectral manifestation of distorted forms of metalloporphins in solid matrices
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In this paper we report the spectral manifestation of different spectral forms obtained for Mg-, Zn-, Pd- and Pt-porphins
in solid matrices (Shpol'skii matrices, solid tetrahydrofuran and rare gas matrices) at cryogenic temperatures. The planar
and two kinds of distorted conformations of Mg-, Zn-porphins in highly-resolved fluorescence spectra have been
detected. For Zn-porphin distorted forms have been detected in the fluorescence and phosphorescence spectra
simultaneously. In the phosphorescence spectra of the Pd- and Pt-porphins the manifestation of the two forms in the
ground state has been proved also. Energy splitting in the phosphorescence spectrum of the Pd-porphin in n-octane at 4,2
K comes to 78 cm-1 for two forms of the Pd-porphin. Under selective excitation in S0-S1 channel the large set of sharp lines was detected for each of two forms and vibrational frequencies have been determined. In highly-resolved
phosphorescence spectra of Pt-porphin in n-octane at 4,2 K we have detected similar manifestation of the two spectral
forms in the phosphorescence spectrum. To estimate the type of molecule distortion the information about the
frequencies of vibronic modes from well-resolved spectra of metalloporphins have been used.
Application of the activation process model to the molecules, positive molecular ions, clusters, and proteins surrounded of IR laser radiation
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In 1990 the activation process model was proposed [1]. Development of the activation process model [2,3] led to
description of either adiabatic or non-adiabatic processes for a molecular structure transformation [4]. The model is
based on two simple assumptions: 1. During the transformation process, the potential energy of a molecular particle
changes discretely or in quanta: the transformation process appears to be a series of quantum subsystems occurring in
sequence (these subsystems may also be defined as identical quantum oscillators); 2. In the field of IR-laser radiation, an
energy exchange between IR radiation and atoms of the molecular particle results in discrete translation of these atoms
which absorb oscillation energy by identical quanta up to molecular structure complete transformation. The numerical
simulation carried out according to the model offered has allowed to describe such processes as: dissociation of SF6
molecule [4] and styrene ion C8H8
+ [5]; selfdiffusion processes in Si, Ge and GaAs clusters [6]; folding and insertion for
the &bgr;-barrel outer membrane protein A (OmpA) of Escherichia coli into dioleoylphosphatidylcholine (DOPC) bilayers
[7]. So, we can see this model has a significant field of application to the activation processes stimulated by IR laser
radiation.
Effects of laser-magnetic blood irradiation in vivo
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Laser-magnetic field action on blood in vivo was studied within a range 440-650 nm. The primary mechanisms of laser-magnetic
blood irradiation in vivo were studied at (1) laser and non-laser irradiation with light of various wavelengths,
(2) autohemo-magnetic-therapy, (3) multicolored over-vein irradiation of the blood, (4) the laser-magnetic field actions.
Hemoglobin is considered as primary photoacceptor of radiation. The dependence of effectiveness of laser action on
light wavelength was compared with known action spectra for blood photostimulation. Magnetic field enhancement of
the laser- induced reactions was discussed as result of magnetic field influence on ferromagnetic hem inclusions and on a
structure of hemoglobin peptide chains. Hemoglobin oxygenation or deoxygenation processes were analyzed as a first
stage of the therapeutic effects depending on a preceding hemoglobin oxygenation degree at pathological state. The laser-
magnetic irradiation causes tendency to the normalization of these process. It is proposed that the secondary reactions
are initiated by reversible structural changes of erythrocytes membrane caused the strong hemoglobin absorption.
Laser induced picosecond electron transfer with participation of excited states for porphyrins covalently linked with electron acceptor
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The dynamics and pathways of relaxation processes in meso-ortho-nitrophenyl substituted octaethylporphyrins OEP-OEPPh(o-NO2) and PdOEP-Ph(o-NO2) occurring with the participation of the S1 and T1 states was studied in polar
Ph((dimethylformamide) and nonpolar (toluene) solvents at 295 and 77 K using pico- and nanosecond laser kinetic
spectroscopy. At 295 K, steric interactions between bulky β-alkyl substituents and ortho-nitro groups of meso-phenyl in
these compounds create optimal conditions for overlapping of molecular orbitals of the porphyrin macrocycle (donor) and
NO2-group (acceptor), thus leading to an efficient photoinduced electron transfer (PET). For free-base OEP-Ph(o-NO2),
PET occurs only via the porphyrin S1 state within 40 ps (dimethylformamide) and 125 ps (toluene), whereas the competing
intersystem crossing S1 ~~>T1 is low probable. For metallocomplex PdOEP-Ph(o-NO2), PET involves both S1 and T1 states. In
the last case, the direct PET from the T1 state to CT state also occurs within picosecond range (20 and 46 ps for
dimethylformamide and toluene, respectively, at 295 K). Rate constants for PET with participation of T1 states are by 3-5
times smaller with respect to those found for PET occurring via the S1 state. For both compounds, the observed long-lived
component (250-700 ns) in decays of the transient T1-Tn absorption is due to the recombination processes of radical-ion
pairs whose lifetime decreases with an increase of the surrounding polarity and is hardly dependent on the presence of
molecular oxygen in the solution. For both compounds, PET is completely absent in rigid solutions at 77 K.