Table of contents

The problems of the theory of so-called nonthermal biological effects of electromagnetic fields are considered. It is shown that these effects can be described by the interaction of electromagnetic fields with the quantum states of molecular biophysical structures and subcellular systems.

The luminescence kinetics of Yb³⁺ donors and Ho³⁺ acceptors is quantitatively studied in gallium—gadolinium garnet (GGG) crystals doped with Yb³⁺ and Ho³⁺ ions. It is shown that the sensitisation of transitions in Ho³⁺ ions occurs due to migration-accelerated (hopping) energy transfer. The microparameters of donor—donor energy transfer are determined at 300 and 77 K. The microparameters of donor—acceptor energy transfer are found at the same temperatures at the first stage of successive sensitisation (resulting in the population of the ⁵I₆ state of Ho³⁺ ions) and at the second stage of successive sensitisation of the ⁵S₂, ⁵F₄→⁵I₈ transition in Ho³⁺ ions. At the second stage of sensitisation, the values of the microparameter of reverse energy transfer are also determined. The possibility of obtaining lasing at sensitised transitions in Ho³⁺ ions in Yb³⁺:Ho³⁺:GGG crystals pumped into the absorption band of Yb³⁺ ions is discussed.

We discuss the physical sense and interpretation of the Maeda—Gallagher experiment (2004) in which the probability of ionisation of Rydberg Li atoms perturbed by the resonance microwave field by a short half-cycle pulse was measured. The periodic dependence of the ionisation probability w_i on the delay time t₀ of the half-cycle pulse with respect to the instant of switching on the microwave field is found. The oscillation period of the function w_i(t₀) is equal to the Kepler period of a Rydberg electron. It is shown that the interpretation of this experiment by the authors in terms of localised wave packets has no grounds and neglects basic processes proceeding in the microwave field. An alternative interpretation is proposed and, as the first step, the structure of the Rydberg wave function formed in the resonance microwave field is studied.

The lasing efficiency of Nd³⁺ ions is studied in laser materials capable of self-Raman frequency conversion. The lasing properties of tungstate and molybdate crystals with the scheelite structure (SrWO₄, BaWO₄, PbWO₄, SrMoO₄, PbMoO₄) activated with neodymium ions are investigated upon longitudinal pumping by a 750-nm alexandrite laser or a 800-nm diode laser. The slope lasing efficiency obtained for a Nd³⁺:PbMoO₄ laser emitting at 1054 nm is 54.3% for the total lasing efficiency of 46%, which is the best result for all the crystals with the scheelite structure studied so far. The simultaneous Q-switched lasing and self-Raman frequency conversion were demonstrated in neodymium-doped SrWO₄, PbWO₄, and BaWO₄ crystals.

The results of video and spectral studies of intense selective visible and near-IR emission of Er₂O₃ powder excited by a 10.6-μm CO₂ laser are presented. The selective emission spectra in the range 460–1700 nm correspond to the Er³⁺ spectra observed upon cathode-, photo- and thermal excitations. Conversion of the CO₂-laser radiation into selective emission is attributed to the excitation of the ⁴I_13/2 energy levels by fluctuations of the local vibration amplitudes and up-conversion transitions to higher energy levels of Er³⁺. Selective emission is applicable for visualisation and digital photo and video recording of laser radiation corresponding to the absorption spectra of oxide screens and conversion of heat into laser radiation upon resonance narrowband pumping of active media in the visible and IR spectral regions.

Systematic errors appearing during measurements of the relative content of carbon dioxide gas isotopic isomers ¹²CO₂ and ¹³CO₂ with the help of mid-IR diode lasers tunable in the 4.35-μm region. The main sources of such errors are the luminescent component in the diode laser radiation, interference of analytic CO₂ absorption lines, as well as temperature and concentration variations of the gaseous medium being analysed. Based on simulations an analytic expression is obtained describing the systematic errors, which can be used to compare the parameters of analytic pairs of lines applied for isotopic analysis.

The frequency splitting due to the Sagnac effect is considered in the active laser gyro with a ring cavity filled with a medium having the high refraction index and nonzero dispersion. It is shown that the medium reduces the gyro-factor by n* times, where n* is the group refractive index. However, in the case of dynamic anomalous dispersion, it is possible in principle to increase the gyro-factor without increasing the ring cavity size.

A single-frequency tunable laser for pumping the cesium frequency standard is studied. It is shown experimentally that the laser emits at a single frequency despite the fact that a few longitudinal modes of the external cavity fall within the reflection band of a fibre Bragg grating (FBG) written in the optical fibre. The laser wavelength can be tuned by varying the pump current of the laser, its temperature, and the FBG temperature. The laser linewidth does not exceed 2 MHz for 10 mW of output power.

The experimental and theoretical investigations of spectral properties of a semiconductor α-DFB laser cavity are carried out. It is shown that in these lasers the curvature of mode gain spectra near the maximum is higher by more than two orders of magnitude than in conventional semiconductor lasers with a Fabry—Perot cavity. The distance between the adjacent axial modes of an α-DFB laser is shorter than in the case of a Fabry—Perot cavity laser of the same length, and its experimental value agrees well with the value obtained in the simple geometrical model, taking into account a zigzag propagation of radiation inside the cavity.

The degree of time coherence of semiconductor lasers operating in the self-intensity pulsation regime is studied by two methods. In the first method measurements were performed with a Michelson interferometer by recording the autocorrelation function, while in the second (spectral) method the spectral density of emission was measured. It is shown that both methods give similar results; however, the spectral method can understate the degree of coherence by the value up to 30% due to a great contribution of spontaneous emission to a recorded signal.

Active laser elements based on polyurethane matrices doped with rhodamine 6G and oxazine 17 dyes are fabricated and tested. Lasing in the yellow—green and red spectral regions is obtained upon excitation of these matrices by a dye laser at 532 nm. The spectral and spatial—angular parameters of emission are studied. It is shown that these parameters are similar for polymer and liquid dye lasers. It is confirmed that pump radiation causes strong thermal distortions of active polymer media and the degree of influence of these distortions on lasing is demonstrated in experiments. The tuning of a laser based on a rhodamine 6G-doped polymer matrix is demonstrated in the range between 579 and 601 nm.

The spontaneous breaking of the symmetry of temporal and spectral characteristics of radiation in counterpropagating waves in solid-state ring lasers (SRLs) is found upon periodic modulation of the pump power. A comparison of experimental results with numerical simulations showed that this effect is well described by a standard SRL model.

The feasibility of experimental investigation of spontaneous magnetic fields in a laser plasma with the help of a fast-electron beam is discussed. A three-dimensional program was written to calculate the kinetics of these electrons in sign-variable magnetic fields and calculations were made for different plasma parameters. An electron energy of ∼100 keV is shown to be sufficient for the investigation of magnetic fields in the plasma plume; this energy for a compressed laser target ranges between 4 and 8 MeV. Electrons with this energy can be generated employing an additional picosecond laser pulse synchronised with the main heating pulse.

The results of numerical simulation of propagation of high-intensity ultrashort pulses in silica glass are presented. It is shown that in the case of a dynamic balance between self-focusing and defocusing induced by ionisation, radiation propagating in the glass over the distance of the order of a diffraction length can be captured to form a quasi-soliton. For certain relations between the parameters of radiation and glass over lengths exceeding the diffraction length, the multifocal propagation regime is possible.

The radii and radii of curvature of Stokes stimulated Brillouin scattering (SBS) beams are measured by the method of moments for smooth nearly Gaussian focused pump beams with the propagation ratio M²_σp≤1.2. It is shown that in the case of sufficiently deeply focused pump radiation, the propagation ratio M²_σS of Stokes beams near the threshold of the transient SBS is smaller than M²_σp and approaches it with increasing the pump pulse energy. It is also found that the radii of Stokes beams at the output from a nonlinear medium are smaller than the radii of pump beams, while the radii of wave-front curvature are close (in modulus) to the radii of wave-front curvature for pump beams.

By using the derived master equations, it is shown that the decay of electronic impurities in a nanocrystal can be described as a collective relaxation of particles. A set of entangled states of impurity atoms is found, which have immunity to this relaxation. These states can be used for decoherence-free quantum processing.

The decay kinetics of photoluminescence (PL) of Eu³⁺ ions (the ⁵D₀→⁷F_j transition) excited by UV radiation (in particular, by a laser) is studied in a Vycor nanoporous glass and transparent polymers doped with Eu(fod)₃ molecules (where fod stands for 6,6,7,7,8,8,8-heptofluor-2,2-dimethyl-3,5-octadionate) using a solution of supercritical CO₂. It is found that the decrease in the PL intensity is caused by the photoinduced transformation of the ligand component of the complex (fod), while the decay rate depends significantly on the type of the matrix. Models of mechanisms of photodissociation of the original complex related to excitation to the singlet absorption band of the ligand (S₀→S₁ transition) in one case and to the ligand—metal charge transfer band in the other case are proposed.

The features of contactless measurements of the surface temperature of bodies by the method of two-colour pyrometry of samples activated by periodic laser pulses are considered. The requirements imposed on the parameters of laser radiation and a measuring circuit are formulated. It is shown experimentally that surface temperatures close to room temperature can be measured with an error not exceeding 3% after elimination of the superfluous static component of the excess temperature. The sensitivity of the method is estimated. Advantages of laser photothermal radiometry with repetitively pulsed excitation of surfaces over the case when samples are subjected to harmonic amplitude-modulated laser radiation are discussed.