Table of contents

LiF crystals with colour centres exhibiting a zero-phonon line (ZPL) at 1080 nm in absorption and luminescence are studied. The decay time of luminescence of colour centres at 10 K is 260 — 280 ns, the ZPL half-width is 4.7 cm^-1, and colour centres are characterised by a weak electron — phonon interaction (the Huang — Rhys factor is S < 0.11). The polarisation analysis of luminescence showed that the transition dipole moments of colour centres are oriented along the crystal axes [100], [010], and [001]. The model of aggregate F₄ colour centres having a spatial structure with three symmetry axes C₂ may correspond to the colour centres studied in the paper.

The results of investigation of an electric discharge XeCl laser with active region apertures 8 × 11, 10 × 15, and 15 × 15 cm are presented. The preionisation of the Ne — Xe — HCl working mixture was performed by soft X-rays and a low-current electron beam, which provided the initial concentration n₀ of electrons in the gas from 10⁶ to 2 × 10¹³ cm^-3. For n₀ < 10¹² cm^-3, the homogeneity of the initial electron concentration and of an electric field in the discharge gap have a considerable effect on the homogeneity of the volume discharge and output characteristics of the laser. For n₀ ≥ 10¹² cm^-3, a homogeneous volume discharge is ignited and is stable if the inhomogeneity of the electric field in the discharge gap does not exceed 10%. A storage capacitor charged to double the voltage of the quasi-stationary discharge operation is sufficient for discharge formation. It is shown that an improvement of the volume discharge homogeneity and a decrease in the size of the discharge chamber make it possible to increase the efficiency of a wide-aperture XeCl laser.

The spectral and lasing parameters of solid laser elements made of a nanoporous glass — polymer composite doped with phenalemine dyes are studied. A high conversion efficiency (35%— 40%) of second-harmonic nanosecond pulses from a Nd³⁺:YAG laser to the 600 — 660-nm region was obtained and a large operating life of the laser elements was demonstrated. A comparison of the parameters of solid laser elements with those of the liquid solutions of the same dyes showed that the conversion efficiency in solid laser elements is as good as that for the dye solutions.

A compact pulsed generator of a kiloelectronvolt electron beam based on an open barrier discharge in a dense gas is proposed and developed. A stable discharge was observed in the experimental setup in a broad range of pressures up to the atmospheric pressure. At moderate pressures of the gas (~ 5 — 20 Torr), the efficient generation of an electron beam was observed with a current density of ~ 1 A cm^-2 and the discharge area of ~ 100 cm². The electron energy was ~ 2 — 10 keV. The pulse repetition rate could be varied from 10 Hz to 10 kHz without changing the electron-beam parameters. By injecting an electron beam into a neutral gas, lasing was obtained at the transitions of a Xe atom in the 2-μm region with an output power of ~ 0.22 mW kHz^-1.

The results of an experimental study of a copper bromide vapour laser with a discharge-channel diameter above 2.5 cm and a high pump-pulse repetition rate are presented. A TGU1-1000/25 high-power tacitron used as a switch made it possible to obtain for the first time a fairly high output radiation power for pump-pulse repetition rates exceeding 200 kHz. At a maximum pump-pulse repetition rate of 250 kHz achieved in a laser tube 2.6 cm in diameter and 76 cm long, the output power was 1.5 W. The output powers of 3 and 10.5 W were reached for pump-pulse repetition rates of 200 and 100 kHz, respectively. These characteristics were obtained without circulating a buffer gas and (or) low-concentration active impurities through the active volume.

A new type of a wide-aperture, high-power and efficient semiconductor laser with emission leaking from an active region and involved in lasing is proposed. The principle of its operation is described. Single-mode semiconductor lasers with output apertures at the optical facet of 5 × 6 μm, 7 × 7.5 μm, and 10 × 10 μm and diffraction-limited divergence angles of emission from 6.9 to 12° in the vertical plane and from 3.3 to 7.7° in the horizontal plane are created for the first time. A single-mode cw output power of 0.5 W is obtained at 980 nm in a single-frequency regime with diffraction-limited divergence angles in the horizontal and vertical planes equal to 5.7° and 12.3°, respectively. In the multimode regime, the output powers of 1.3 and 3.0 W were obtained with small divergence angles for ridge widths of 10 and 50 μm, respectively.

Stationary lasing at two competing lines sharing an upper level is studied. Based on the expressions for the gain obtained earlier, the possible lasing regimes are considered (at one or two lines) and approximate formulas are derived for determining the output power in each line. These formulas are shown to be the generalisation of the Rigrod formula to the case of simultaneous lasing at several lines.

A three-dimensional numerical diffraction model of a slab laser with a hybrid resonator is developed and used for studying the phase locking of two lasers optically coupled through the edge of the output mirror. Numerical analysis of phase locking of industrial CO₂ slab lasers shows that such a locking is possible for an appropriate choice of coupling parameters. It is found that the destructive effect of the active medium caused by an increase in the pump intensity can be minimised. It is shown that as the pump intensity is increased, the lateral radiation pattern of the output radiation improves while the beam is broadened in the transverse direction due to excitation of higher-order waveguide modes.

A model of the so-called short hologram, which does not exhibit in-depth diffraction deformation of the fine speckle pattern of the recording fields, is studied. The investigation is performed by the example of a thermal hologram recorded by two speckle waves, which is the output mirror of a ring laser produced as a result of this recording. It is shown that the ability of this short hologram to select a wave conjugated to a speckle signal in the mode of the holographic laser depends both on the degree of mutual mixing of the speckles of recording beams in the hologram volume and on the effects of its saturation by the beams. The maximum accuracy of phase conjugation of speckle radiation in the holographic Nd:YAG laser achieved upon the best selection of the conjugate wave by the short thermal hologram was 93%.

Nonlinear optical characteristics of an aqueous colloidal solution of As₂S₃ are studied by the Z-scan technique at the wavelength 1064 of a 25-ns Nd:YAG laser. The measured values of the nonlinear refractive index and the third-order nonlinear susceptibility are found to be −2.8 × 10^-11 and −4.7 × 10^-12 CGSE units, respectively. The nonlinear absorption coefficient of the chalcogenide solution is found to be 1 cm GW^-1.

The possibility of amplification of pulses of squeezed light in the regime of triggered optical superradiance is analysed. The kinetic equations are obtained which describe the dynamics of cooperative development of the population inversion and dispersion of the quadrature components of polarisation of optical centres interacting with the triggering-pulse field in the squeezed vacuum state. The dependence of the squeezing degree of the superradiance field on the squeezing degrees of the triggering-pulse field and polarisation of an amplifying medium is determined. It is shown that in the case of a sufficiently strong squeezing of the medium, the intensity of the squeezed quadrature component of the superradiance signal is lower than that of an incoherent spontaneous background. Therefore, the superradiance field can be characterised not only by a classical squeezing (when the dispersions of quadratures are not identical) but also by a quantum squeezing (when the dispersion of one quadrature is smaller than its vacuum value).

Nonstationary transmission (reflection) of two time-separated ultrashort laser pulses by thin semiconductor films is studied. Photons of one of these pulses generate biexcitons in the films due to two-photon absorption from the crystal ground state, while photons of the other pulse induce an optical exciton — biexciton conversion. Several basically new effects in nonstationary light transmission (reflection) are found and interpreted.

The efficiency of stimulated scattering of laser radiation in heptane is studied. The reasons for the shortening of a reflected pulse and a decrease in the reflection coefficient with increasing the spectral width of pump radiation are analysed. A mechanism of photodissociation of molecules in a nonlinear medium is proposed that explains the reduction in the efficiency of stimulated scattering.

The formation of a periodic structure of the optical field of a wide-aperture laser with inertial Kerr phase nonlinearity is considered. The conditions for the appearance of one-dimensional periodic wave structures propagating along the aperture are found and their properties are studied.

The penetration of an H wave through a waveguide whose radius varies continuously from about the wavelength size to subwavelength dimensions (of the order of 1/10 wavelength) is calculated. The method for the field analysis is developed and the range of its applicability is studied by considering some numerical examples. The dependence of the transmission coefficient of a tapered waveguide on the radiation wavelength and on the profile steepness of the waveguide is studied. It is shown that a sharper decrease in the waveguide radius provides higher values of the field transmission coefficients.

The process of excitation of whispering-gallery waves (WGWs) in optical fibres (microcavities) with the help of a bitapered fibre is analysed. It is shown that useful information on the WGW modes can be obtained from the spectrograms recorded by scanning the exciting-radiation frequency. Based on the geometrical-optic approximation, the longitudinal sizes of the WGW modes are estimated and it is shown that the ultimate diameter of the fibre exists for optical fibres (microcavities) where a mode can be still excited with the help of a bitapered fibre.

The spectral profiles of the gain in an erbium-doped fibre amplifier, incorporated into a recirculating fibre ring, are experimentally investigated. The fibre ring was excited by a superfluorescent fibre source. A procedure for measuring the spectral gain profile is developed, and the criterion of gain-profile uniformity evaluation in the case of broadband radiation is proposed. The influence of the shape of the input radiation spectrum, the pump level, and the composition of the active fibre on the uniformity of the spectral gain profile is studied. It is found that, the uniformity reaches its maximum at a certain pump level. It is shown that, to obtain a maximum number of recirculation cycles for a broadband optical signal, one has to optimise parameters of the fibre amplifier together with parameters of the fibre source of radiation in the active recirculation interferometer.

A fibre Raman amplifier operating at a wavelength of 1.65-μm is fabricated. A two-stage phosphosilicate fibre Raman converter of 1.53-μm radiation for pumping the Raman amplifier is designed and tested. The amplifier pumped by a phosphosilicate fibre Raman converter can operate with a maximum of the gain band ranging from 1.6 to 1.7 μm. A fibre with a core of a high (25%) molecular content of GeO₂ serves as an active medium for the Raman amplifier. The gain obtained for different powers of the input signal is 22 — 25 dB. Our calculations show that the use of a standard telecommunication fibre (with a lower content of GeO₂) allows one to increase the gain in this scheme by reducing fibre splicing losses.

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