Table of contents

A two-mode laser based on the colour centres in an Li:RbCl crystal and pumped by several laser diodes was constructed. The tuning range was 2.7 — 3.28 μm. The use of a laser with an intracavity absorbing methane cell made it possible to observe saturated-dispersion resonances at the R-branch lines of the ν₃ band of the methane molecule with a spectral resolution of 300 kHz.

The light-oxygen effect (POE) represents damage (and at low optical doses, activation) of cells by photogeneration of molecular singlet oxygen from O₂ dissolved in cells, in accordance with the reaction: ³O₂+hν→¹O₂→ biological effect. The phases of evolution of the LOE are similar to the phases, observed in cell experiments, of the photodynamic effect (PDE) the mechanism of which is the basis of the familiar method of photodynamic cancer therapy. The reported proofs of the occurrence of the LOE are in the form of detailed spectra of the biological action of optical radiation on cells recorded in four spectral intervals with the aid of tunable lasers. Allowances are made for the relationships governing a new type of cell excitation, associated with reversible structural transitions in the biomembrane. A demonstration is reported of the same efficiency of cw and pulsed irradiation. An analysis is made of the reasons why the optical doses initiating the PDE and the LOE are comparable. The results are given of the first experimental applications of the LOE in tumour therapy. Identification of the primary photoacceptor (O₂) in cell biostimulation and photodestruction provides a scientific basis for the development of low-intensity laser light-oxygen cancer therapy methods.

A method, based on the optoacoustic effect for determination of the spatial distribution of the light intensity in turbid media and of the optical characteristics of such media was proposed (and implemented experimentally). A temporal profile of the pressure of a thermo-optically excited acoustic pulse was found to be governed by the absorption coefficient and by the spatial distribution of the light intensity in the investigated medium. The absorption coefficient and the reduced light-scattering coefficient of model turbid water-like media were measured by the optoacoustic method. The results of a direct determination of the spatial light-intensity distribution agreed with a theoretical calculation made in the diffusion approximation.

An investigation of the influence of the photodynamic effect on S.aureus and E.coli bacteria in the presence of blood cells was made by the laser photothermal cytometry method. Elements of the theory of the photothermal method are considered for the case of pulsed lasers used in microscopy. Chlorin in doses of 0.02 mg litre^-1 was used as a photosensitiser. The results of the investigation made it possible to propose the possibility of an immunomodulation effect caused by introducing photoactivated chlorin into the cell — microbe system. It was found that the photothermal parameters of the cells interacting with microbes in the presence of photoactivated chlorin differed from the parameters of intact cells much less than in the absence of chlorin. However, a more pronounced bactericidal effect was observed in the samples treated with chlorin.

A demonstration is given of the feasibility of two-photon excitation of aluminium phthalocyanine and of the pharmaceutical preparation 'Fotosens', used in photodynamic therapy. The excitation source was an Nd:YAG laser emitting at the 1064 nm wavelength. The spectra of the two-photon-excited luminescence were obtained and the two-photon absorption cross sections were determined.

An investigation was made of the ratios of the intensity I_df of the singlet-oxygen(¹O₂)-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine (ZnTBPc), with the maximum at λ = 685 nm, to the intensity I₁₂₇₀ of the photosensitised phosphorescence of ¹O₂ with the maximum at λ = 1270 nm in deuterated benzene when excited with λ = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25 — 0.7 mJ cm^-2) and on the concentration of ZnTBPc (0.06 — 3.4 μM), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence I_df⁰/I₁₂₇₀⁰ varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc. The intensity I_df⁰ decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient α =(I_df⁰/I₁₂₇₀⁰)k_r/(γ_f[¹O₂]₀[ZnTBPc]), where [¹O₂]₀ is the zero-time concentration of ¹O₂ after a laser shot; k_r is the rate constant of radiative deactivation of ¹O₂ in the investigated solvent; γ_f is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was ~2 × 10¹¹ M^-2 s^-1.

The changes in the state of polarisation of laser radiation transformed by biofractal objects are examined. The orientational angular structure of the matrix elements of the operator representing the optical properties of biofractals with different morphological structures (mineralised collagen fibres and myosin bundles) is investigated. An optical model for the description of fractal laser fields under the conditions of single light scattering is proposed.

An optical approach to the problem of modelling and diagnostics of the structures of biofractal formations was considered in relation to human bone tissue. A model was proposed for the optical properties of this tissue, including three levels of fractal organisation: microcrystalline, macrocrystalline, and architectural. The studies were based on laser coherent polarimetry ensuring the retrieval of the fullest information about the optical and polarisation properties of bone tissue. A method was developed for contactless noninvasive diagnostics of the orientational and mineralogical structure of bone tissue considered as a biofractal.

An ab initio calculation of the potential energies was made for the electronic states of ionic excimer molecules consisting of rare gases (Rg = Ne, Ar, Kr and Xe) and alkali metals (A = K and Rb). The calculation included the ground 1¹∑⁺ states and the first excited singlet 2¹∑⁺, which correspond to the Rg(¹S) + A⁺(¹S) and Rg⁺(²P) + A(²S) separate limits, respectively. The calculated results predict that the emission based on transitions from the 2¹∑⁺(ν'=0) states to the higher ν'' levels of the 1¹∑⁺ states is characterised by the highest relative transition probabilities, which are promising for lasing in the vacuum and extreme ultraviolet (VUV/XUV) spectral ranges. Moreover, bound — free VUV emission bands were observed for electron-beam-pumped gas mixtures of Xe or Kr with a hot Rb or Cs alkali vapour. The observed four emission bands were assigned to the 2¹∑⁺ →1¹∑⁺ transitions in the rare-gas — alkali ionic excimers Xe⁺Rb, Kr⁺Rb, Xe⁺Cs, and Kr⁺Cs, respectively.

Parallax effects in laser Doppler spectroscopy, associated with the variation of the scattering angle during motion of a particle through the probed volume, were investigated by a numerical simulation method based on the Mie scattering theory. It was found that, in general, the shifts of the spectral profile parameters (the average frequency, broadening, asymmetry, and kurtosis) become significant as the parallax number N_ψα=(2/π)ψα (ψ is the angular size of the probed volume, α = πd/λ is the relative particle diameter) increases. The anomalous ranges of the parameters of the particle and of the optical system, in which marked distortions (such as the polymodal nature and the splitting of the spectral profile) are observed even for a low parallax number (N_ψα ≪ 1), were discovered.

A system of unexcited three-level atoms, located in a nonresonant laser field, was examined. One of the excited levels in the system becomes populated under the influence of a weak optical signal, as a result of which the atoms resonate with the laser field. A consequence of this is intense scattering of the laser radiation and particularly excitation of the hitherto unexcited modes of the cavity in which the system of atoms is located. The system considered thus possesses states which are specially sensitive to external agencies and therefore sensitive optical-radiation detectors can be based on these states.

The problem of enhancing the contrast of optical images in a strongly scattering medium by means of luminescent and absorbing dyes, topical in laser tomography, is examined. Preparations based on diphthalocyanine compounds were selected on the grounds of their tropism and resistance to the action of heat and light. Images with enhanced contrast in model scattering media (an aqueous solution of milk and margarine) were obtained in the IR region of the spectrum using the radiation of a picosecond neodymium laser.

The spatial distribution of the scattered-radiation energy during focusing, in atmospheric air, of the fourth-harmonic beam of a pulsed neodymium laser (λ = 264 nm) with an annular cross section was studied experimentally. Shortening of the UV scattered-radiation by a factor of 2 — 5, compared with the duration of the laser pulse, was observed. An interference structure of the scattered radiation, varying with increase in the laser-pulse energy, was recorded. The diffraction rings and bands originating from screens were transformed into analogous diffraction rings and bands from additional screens. This can be accounted for by the scattering of the laser beam on a gas perturbation or on a particle in the caustic. Experiments were performed on the scattering of radiation with λ = 0.63 μm on formations with an abrupt boundary, which confirmed the above hypothesis.

Phase locking of the radiation of two ring waveguide CO₂ lasers with a common cavity and unidirectional lasing was achieved for an output power of about 20 W. Measurements of the fringe visibility of the radiation intensity distributions in the far-field zone agreed qualitatively with the calculations for plane waves.