Nikolai I. Koroteev

Rise and decay kinetics of photosensitized singlet oxygen luminescence in water. Measurements with nanosecond time-correlated single photon counting technique

The time-correlated single photon counting technique was applied to the measurement of photosensitized singlet oxygen luminescence induced by flash laser excitation. Rise and decay kinetics of this luminescence has been measured with 10 ns resolution in aqueous solutions of tetra (p-sulfophenyl)porphyrin at various oxygen pressures. The rise kinetics are shown to be determined by the process of energy transfer to oxygen from the triplet state of the photosensitizer. The lifetime of singlet molecular oxygen in water was measured with high precision: τΔ = 3.09±0.06 μs. The rise and decay kinetics of the singlet oxygen luminescence in aqueous suspensions of porphyrin-containing yeast cells were detected.

Enhancement of second-harmonic generation with femtosecond laser pulses near the photonic band edge for different polarizations of incident light

We present experimental evidence of enhancement of second-harmonic generation as a result of an increase of the fundamental-field energy density within a multilayer structure near the photonic band edge.

Polarization sensitive coherent anti-Stokes Raman scattering spectroscopy of the amide I band of proteins in solutions

Polarization sensitive coherent anti-Stokes Raman scattering (PCARS) spectroscopy is a fruitful technique to study Raman vibrations of diluted molecules under off-electron resonant conditions. We apply PCARS as a direct spectroscopic method to investigate the broad amide I band of proteins in heavy water. In spontaneous Raman spectroscopy, this band is not well resolved. We fit a number of spectra taken of each protein under different polarization conditions, with a single set of parameters. It then appears that some substructure is observed in the amide I band. From this substructure, we determine the percentage of alpha-helix, beta-sheet, and random coil for the proteins lysozyme, albumin, ribonuclease A, and alpha-chymotrypsin.

Strong selective excitation of Raman-active vibrations and energy transfer between low-lying vibrational states of a CO2 molecule studied by PARS and CARS

Abstract We experimentally demonstrate the novel technique of inducing the highly nonequilibrium distribution of molecules over vibrational states by two-frequency coherent Raman excitation. The technique can be used for selective excitation of totally symmetric and other Raman-active molecular transitions. Two counter propagating focused laser beams (second harmonic of Nd: YAG and dye laser) were used to induce population difference changes at the 0000–1000 transition in CO2 molecules. The excitation and relaxation kinetics of this and neighbours vibrational modes of CO2 were studied both by CARS and PARS. Vibrational excitation of up to 20% of the total number of irradiated molecules is measured; previously unknown desactivation constant of CO2 (1000) and CO2 (0200) states via CO2 (0110) state is estimated to be K = (3±1) × 1 5s-1torr-1.

High-resolution cw CARS spectra of liquid nitrogen dissolved in liquefied Ar, Kr, O 2 , CO, and CH 4

The high-resolution cw CARS technique has revealed solvent-induced alterations in linewidth and position of the 2326.5-cm(-1) Raman line of liquid, nitrogen, which becomes strongly broadened when Kr or CH(4) is added and is almost unaltered in solutions with CO and O(2). The interpretation is given in terms of motional narrowing and vibrational dephasing theory.

Generation of the second optical harmonic in porous-silicon-based structures with a photonic band gap

Efficient generation of the second optical harmonic is observed experimentally in a multilayer periodic structure based on porous silicon. The second-harmonic signal is much stronger than the signal from a uniform porous silicon layer or from the single-crystal silicon substrate. The orientational dependence of the second-harmonic signal is isotropic. The second-harmonic intensity as a function of the reflection angle reaches a maximum in the direction corresponding to the minimum phase detuning in a multilayer periodic structure.

Saturation effects in cars: Collisionally narrowed raman spectra of diatomic gases

Abstract The saturated linescape of the CARS signal is calculated for Q-branch transitions (Δ J =0) in simple diatomics (N 2 , O 2 , etc.) from low pressures up to pressures where the J signature of a Q band is collapsed and collisionally narrowed. The asymmetry of the saturated CARS bandshape is shown to provide insight into the broadening mechanism of a Raman transition. The pumping rate of the molecules into the ν = 1 vibrational state due to the CARS saturation is shown to be very high.

Time-resolved spontaneous and coherent raman scattering of Ni-octaethylporphyrin in excited electronic states

Abstract The results are presented of a detailed analysis of the vibrational structure of the excited triplet electronic state T d of Ni-octaethylporphyrin (Ni-OEP) in solution by means of spontaneous and coherent Raman scattering spectroscopy. The application of these two methods generated complementary information about the characteristics of the T d state.

Subpicosecond anisotropic CARS studies of vibrational mode-selective photoexcitation and relaxation of trans-stilbene. First few picoseconds

Abstract Sub-picosecond coherent anti-Stokes Raman scattering (CARS) spectra of singlet trans-stilbene (tSB) in heptane have been obtained using UV excitation and CARS probe for the 0–5 ps time range. The excited state CARS spectra of tSB in heptane exhibits mode-selective dynamics. Different temporal behaviors of the three investigated S1 Raman bands (1181, 1242 and 1565 cm−1) are observed. These results are discussed with respect to possible role of vibrational energy redistribution and associated conformational changes.

Stilbene isomerization dynamics on multidimensional potential energy surface. Molecular dynamics simulation

Abstract The dynamics in the photoisomerization of isolated cis-stilbene, especially the dynamics leading to the intermediate twisted configuration is explored by molecular dynamics simulation. Comparison of the dynamics of the trans and cis isomers shows that for cis-stilbene the time required to reach the twisted configuration is an order of magnitude or two less than for trans-stilbene, due only to the specific steric interactions, and not to any difference in the potential functions or parameters. A barrier of between 510 and 640 cm−1 along the torsional coordinate from the cis side is estimated for isolated molecule, accounting for a transition to the intermediate in approximately 300 fs.