Table of contents

The possibilities of separating the fundamental optical mode in composite waveguides by selecting the structure of amplifying regions are analysed. Conditions are presented under which the fundamental mode preserves the highest gain at any saturation.

Pulses arising when the cathode of a photomultiplier emits two electrons are studied. It is shown experimentally that under certain conditions, emission of individual photoelectrons forming a pair cannot be considered as independent but should be described as a single two-photon photoeffect.

The spatial distributions of photoinduced electric fields are calculated based on the model of the current mechanism of optical poling of isotropic media and the efficiencies of the main poling schemes differing in the geometry of crossing beams are estimated. It is shown that the volume optical poling in a certain interval of small angles of crossing beams is the most promising for producing homogeneously distributed photoinduced electric structures of a large size.

The distribution of the UV power density in the 337.1-nm C ³Π_u — B ³Π_g band over the output beam cross section of a transverse-discharge-pumped nitrogen laser is studied experimentally. It is shown that for the nitrogen pressure up to tens of torr and large laser pulse durations, the radiation power density from the cathode discharge region is lower than that from the rest part of the discharge gap. The potential distribution in the cathode discharge region is analysed theoretically. It is shown that the length of the cathode region with a low radiation power density observed in the experiment corresponds approximately to the length of the dark Faraday space in an anomalous glow discharge.

The effective deactivation rate constants are calculated for I₂(X) molecules at vibrational levels with v ≥ 30 colliding with N₂ and O₂ molecules in the medium of a chemical oxygen–iodine laser. The calculated constants (4×10^-12 cm³ s^-1 and 3×10^-12 cm³ s^-1) are less by half plus than the corresponding constants found earlier in the paper of Lawrence et al., where the dissociation of I₂ was neglected in calculations.

The method is proposed for calculating dynamic synchronisation regions of a ring laser with a periodic frequency support of a special type. The proposed algorithm in essence taking into account the special type of the support allows the search for minimal widths of regions when the support parameters change. The widths of the regions are calculated as an example for the case of the harmonic carrier modulation as a harmonic envelope (three-frequency support) and an envelope of the 'soft' meander type (multifrequency support).

Superluminescent diodes (SLDs) based on double quantum-well (AlGa)As/GaAs heterostructures emitting between 800 and 900 nm are studied experimentally. These SLDs provide a high enough output power in the emission bandwidth more than 55 nm at much shorter active channel lengths than SLDs based on similar single quantum-well heterostructures. Despite the high injection current density, the service life of the SLDs exceeds 10000 hours.

Based on analysis of two-dimensional numerical calculations and experiments performed on the PALS setup, the similarity relations are obtained for determining pressure in a condensed matter irradiated by a short laser pulse of intensity 5×10¹³–5×10¹⁴ W cm^-2.

It is proposed to use narrow optical resonances, corresponding to the hyperfine structure components of emission transitions in I₂, as frequency references to stabilise laser radiation frequency in the spectral range from 0.8 to 1.3 μm. To obtain such resonances and investigate the hyperfine structure of emission transitions, an experimental setup is built which consists of a saturated absorption laser spectrometer and a three-level laser spectrometer. Excitation is performed by the second harmonic of a cw Nd:YAG laser and probe radiation in the range from 968 to 998 nm is generated by an external cavity diode laser. The radiation beams from both lasers are combined in a cell with iodine vapour, excitation in the cell being performed in the regime of two counterpropagating waves. It is shown that upon phase modulation of exciting radiation, narrow resonances, having the form of the dispersion dependence, appear at the centre of Doppler lines in absorption and emission. These resonances can be used as references to stabilise the laser frequency. The results of the study of the hyperfine structure of emission lines at the (J' = 57, v' = 32) → (J'' = 58, v'' = 48) transition upon excitation at the (J'' = 56, v'' = 0) → (J' = 57, v'' = 32) transition are presented.

The mean received power of partially coherent cw laser radiation scattered in the atmosphere is calculated depending on the spatial coherence of the initial field and the angular divergence of a laser beam formed by a circular output aperture. It is shown that due to diffraction on the circular aperture, the dependence of the mean radiation power on the divergence angle is nonmonotonic and has a maximum. The divergence angle corresponding to this maximum is determined by the spatial coherence of the initial field. The possibility of controlling the adaptive loop of the laser system by means of signals backscattered in the atmosphere is discussed.

A nonreciprocal ring optical resonator with the simplest type of nonuniformity in the form of two interacting scatterers is considered. A boundary problem of a periodic type allowing one to write the characteristic equation for determining eigenfrequencies is formulated. Analytic expressions for eigenfrequencies and the distribution coefficient of travelling waves in the mode are derived under the assumption of relative smallness of the reflection coefficient and the nonreciprocity parameter. The peculiarities of splitting these frequencies and the structure of the eigenfrequencies (resonator modes) corresponding to them are discussed.

The separation of nitrogen isotopes is studied upon successive single-photon IR excitation and UV dissociation of ammonia molecules. The excitation selectivity was provided by tuning a CO₂ laser to resonance with ¹⁴NH₃ molecules [the 9R(30) laser line] or with ¹⁵NH₃ molecules [the 9R(10) laser line]. Isotopic mixtures containing 4.8% and 0.37% (natural content) of the ¹⁵NH isotope were investigated. The dependences of the selectivity and the dissociation yield for each isotopic component on the buffer gas pressure (N₂, O₂, Ar) and the ammonia pressure were obtained. In the limit of low NH₃ pressures (0.5—2 Torr), the dissociation selectivity α(15/14) for ¹⁵N was 17. The selectivity mechanism of the IR+UV dissociation is discussed and the outlook is considered for the development of the nitrogen isotope separation process based on this approach.

The kinetics of photoluminescence of a EuFOD₃ metalloorganic compound doped into a nanoporous Vycor glass by the method of supercritical fluid impregnation is studied. The lifetime of luminescence of EuFOD₃ molecules in pores excited by an excimer XeCl laser was 40 μs, which is considerably smaller than this lifetime (150—890 μs) in solutions. The quantum yield of luminescence of EuFOD₃ was estimate as ≈4×10^-4.

A computer-controlled integrated optical waveguide sensor based on an optical waveguide of the diffusion type with the low attenuation coefficient is developed and studied. It is shown that the response time of the sensor is ≈0.15 s. According to tests and computer simulations, the sensor can detect gaseous ammonia in air with the limiting theoretical concentration of ≈0.1 ppm for the signal-to-noise ratio no less than 20.

The energy and spectral parameters of emission of a barrier discharge in chlorine and its mixtures with inert gases are studied experimentally. The barrier discharge in chlorine was homogeneous at pressures up to ≈9 Torr and its spectrum contained the ³Π_2g→³Π_2u, ³Π_2g→³Σ_2u⁺ and ¹Σ_u⁺→¹Σ_g⁺ bands of Cl₂* molecules. After the addition of an inert gas, the 257.8-nm ³Π_2g→³Π_2u band made the main contribution to the spectrum. The maximum efficiency and power of the Cl₂ excilamp were obtained for the chlorine—argon mixture and amounted to 0.7% and 1.3 W, respectively.

A centrifugal bubbling singlet-oxygen gas generator is developed in which chlorine with helium are injected into the rotating layer of the alkali solution of hydrogen peroxide through cylindrical nozzles directed at an angle of 30° to the bubbler surface. The concentrations of water vapour and O₂ (¹Δ) and the gas temperature were determined by using the multichannel recording of the emission bands of oxygen at 634, 703, 762 and 1268 nm. For the chlorine and helium flow rates of 60 and 90 mmol s^-1, respectively, the specific chlorine load of 3.2 mmol cm^-2, a total pressure of 100 Torr in the working region of the gas generator and the oxygen partial pressure of 36 Torr, the chlorine utilisation was 90% and the content of O₂ (¹Δ) was ≈60%. For the ratio of the flow rates of chlorine and the alkali solution of hydrogen peroxide equal to 1 mol L^-1, the water vapour content was ≈25%. The chemical efficiency of the oxygen—iodine laser with this gas generator achieved 23% for the specific power of 12.7 W cm per 1 cm³ s^-1 per pass of the solution through the gas generator.