A. N. Rubinov

Interaction of interference laser field with an ensemble of particles in liquid

Abstract The dependence of the spatial redistribution of microparticles in a suspension under the action of an interference laser field on the particle parameters and field characteristics is theoretically analyzed. The experimental results illustrating the optical trapping of an ensemble of polymeric balls and other microparticles in liquid by interference fringes of the He–Ne laser radiation ( λ =632.8 nm) are presented. The interferometric trapping of microparticles was observed at a light power as low as ∼2 mW. It was also found that regular crystal-like structures of particles are formed as a result of interaction of the particle ensemble with the gradient light field produced by a softly focused single He–Ne laser beam.

Simultaneous oscillation of several independently tunable spectral lines in a distributed feedback dye laser

Abstract A simple method is proposed which allows obtaining distributed-feedback laser action simultaneously at several spectral lines of any wavelength with independent tuning within the gain profile of the dye.

Localization of Spherical Particles under the Action of Gradient Forces in the Field of a Zero-Order Bessel Beam. Rayleigh–Gans Approximation

The amplitude of the gradient force acting on a transparent spherical particle in the field of a zero-order Bessel beam has been calculated in the Rayleigh–Gans approximation. The expression obtained for the gradient-force amplitude takes into account the heterogeneity of the acting radiation in the volume of the particle. The optimal conditions of trapping and transportation of the particle (parameters of the particle, liquid, and of the Bessel beam) to the localization region have been determined using the solution of the kinetic equation of particle motion in a liquid. It is shown that for certain relationships between the particle radius and the Bessel beam width the localization region is shifted relative to the central maximum of the beam. This is due to the equal action of the gradient forces caused by the central maximum and the first interference ring of the Bessel beam. A qualitative comparison of the results obtained with the known experimental data has been performed.

New high-efficiency biscoumarin laser dyes

Abstract A new type of bifluorophoric molecule consisting of two heterocycle-linked coumarin fluorophors is studied. A high laser efficiency, a broad tunability range and good photostability for two synthesized biscoumarins are observed. One of the proposed biscoumarins covers the green spectral region where the efficiency of known laser dyes is relatively low.

Holographic DFB dye lasers

A new simple type of DFB dye laser is proposed. The laser consists of a dye cell and a transparent phase holographic grating mounted on the front window of the cell. In the experiment, high-quality stable transparent holographic gratings were recorded in bichromated gelatine with a single mode He-Cd laser. When pumped perpendicular to the surface of the grating the DFB laser emitted a narrow spectral line independently of the width and the position of the pump spectrum. A linewidth of 0·01 nm was measured under pumping with broadband radiation of 20 nm spectral width. Either a set of holographic gratings of a different period or a fan-shaped grating may be used in the laser for stepped or continuous spectral tuning.

Dipole Moments of Phenylnaphthylamine Fluorescence Probes and Study of Dielectric Interactions in Human Erythrocyte Ghosts

Electrooptical absorption and emission methods were used to measure the dipole moments of 1-phenylnaphthylamine (1-AN) and 1,8-anilinonaphthalene sulfonate (1,8-ANS) fluorescence probes in the ground and excited states. The measurements were performed in cyclohexane (1-AN) and dioxane (1-AN and 1,8-ANS). Our results show that the charge distribution in 1-AN differs substantially from that in 1,8-ANS. The spectral dependence of electrooptical coefficients in the case of 1,8-ANS indicates that the absorption band is a superposition of several (at least two) electronic transitions. We found that the electronic spectra of 1-AN in erythrocyte ghosts are inhomogeneously broadened. Due to inhomogeneous broadening it is possible to excite selectively molecules located at different sites. Dielectric interactions (given by the dielectric constant) were investigated from the position of the maximum of the fluorescence quantum spectra of 1-AN. The dielectric constant of human erythrocyte ghosts varies from about 6.7 ± 0.8 to about 17.6 ± 3.5, depending on the excitation frequency and, consequently, on the location of the probe.

The effect of an external mirror on the characteristics of an N2 laser-pumped distributed feedback dye laser

Abstract The effect of an external mirror on the DFB dye-laser parameters was investigated experimentally. When a 100% mirror was used, the output energy quadrupled, the divergence decreased to the diffraction limit. Besides the study of the improvement of laser parameters, the temporal behaviour of the amplified spontaneous emission and the DFB dye-laser action were simultaneously investigated.

Generation of tunable picosecond pulses in a simple distributed feedback dye laser under N2-laser pumping

Abstract Simple possibility of single tunable picosecond pulse generation in a conventional inexpensive distributed feedback dye laser (DFDL) is demonstrated. It is shown that when a TEA N 2 -laser is used for pumping no diffraction grating is necessary in the DFDL optical scheme for operation in the picosecond regime. Hence wide-range spectral tuning from 357 to 665 nm was easily achieved. When pumped with a 0.6 ns 40 kW pulse of the TEA N 2 -laser the DFDL generated pulses as short as 7 ps with time-bandwidth product better than 0.6 and peak power ∾ 10 kW. At a repetition rate of 50 pps the shot-to-shot energy stability of a single picosecond pulse was ±18% at ±7% stability of the TEA N 2 -laser.

Nonresonance Mechanisms of Biological Effects of Coherent and Incoherent Light

Two mechanisms of the nonresonance action of light on biological systems are considered. The first of them is caused by gradient effects arising upon interaction of a biological system with spatially inhomogeneous radiation. The second mechanism is determined by light-induced dipole-dipole interactions between biological particles. The first mechanism is characteristic of coherent radiation. A speckle structure arising upon interaction of coherent light with a biological system gives rise to gradient forces, which depend on the intensity of the incident light and the properties of an object. It is shown that the action of the gradient forces on microparticles causes a selective increase in the kinetic energy of the particles. Due to random pulsations of speckles in living tissue, this effect is equivalent to an increase in the “partial” temperature of the particles, which depends on their size and properties. The second mechanism manifests itself both upon coherent and upon incoherent irradiation of a biological object. This mechanism is determined by interactions between oscillating dipole moments of neighboring particles (cells, organelles, biomolecules) induced by incident radiation. The second mechanism is shown to be observed for linearly polarized radiation only. For each mechanism, the forces acting on biological particles are calculated.

Orientation of red blood cells and rouleaux disaggregation in interference laser fields.

The effect of interference laser fields on red blood cells (RBCs) was investigated both theoretically and experimentally. The optical trapping and orientation of individual RBC in interference fringes were observed. It was found that RBC rouleaux undergo disaggregation under the action of interference laser fields. To describe the effect of RBC orientation in interference fringes, we used the equation for torque exerted on a discoid dielectric particle in a gradient light field. The experimental results are in agreement with the predictions of the developed theoretical model.