Table of contents

We demonstrate the first bismuth-doped fibre amplifier operating in the second transmission window of silica-based fibres. At a pump power of 460 mW and pump wavelength of 1230 nm, its gain reaches 24.5 dB at 1320 nm, with a gain bandwidth of 37 nm, saturation power near 10 mW, and noise figure of 5 dB.

A high-repetition-rate CO₂ laser with the inductive-capacitive discharge stabilisation is studied for the first time. A multisection discharge gap of length 250 mm was formed by pairs of anode — cathode plates arranged in the form of a broken line. The width of the discharge region between each pair of the plates was ∼ 1.3 mm and height ∼ 12 mm. The cross section of the laser beam on the output mirror of the resonator was ∼ 6 × 8 mm. The maximum output energy of the laser using the CO₂:N₂:He=32:32:96 Torr mixture was 15.9 mJ, the lasing efficiency being 1.7%. For a relatively low gas flow rate of 19 m s^-1, a CO₂ laser pulse repetition rate of 3 kHz was achieved, the relative root-mean-square deviation of the pulse energy being within 5%. The average output power of the laser was ∼ 40 W.

UV lasing is studied in nitrogen and the N₂ — SF₆ mixture pumped by a volume discharge initiated by a runaway-electron preionised diffuse discharge (REPDD) produced in an inhomogeneous electric field. It is shown that lasing at a wavelength of 337.1 nm is observed at pressures up to 2.5 atm without any preionisation source. At a pressure of 0.5 atm with the use of blade electrodes and the N₂:SF₆=10:1 active medium of length ∼ 6 cm, the output laser energy of ∼ 2 mJ was achieved for the pulse power of 0.55 MW. The REP DD pumping regime is compared with the regime of pumping by a volume discharge produced by a preionisation source.

We report a computer simulation study of light absorption, scattering and emission at 397 nm in an ultracold calcium ion plasma under resonant excitation. The results point to spectral asymmetry of light scattering, nonlinear absorption, and emission in the plasma. An approach is proposed for ultracold plasma diagnostics using resonant optical characteristics.

A high-strength neodymium laser glass (SNLG) based on an alumoborophosphate composition is developed and synthesised; its physicochemical, spectral, luminescent, and lasing characteristics are studied. It is found that the chemical stability and thermal resistance of the new glass are considerably higher than the corresponding characteristics of known neodymium-doped phosphate laser glasses. Investigations of lasing upon longitudinal diode pumping showed that, due to the higher thermal resistance, the new glass allows one to obtain output powers twice as high as those of industrial GLS22 glass.

A cobalt-doped GGG crystal is grown and its properties are studied. The absorption and fluorescence spectra in the visible and IR regions are measured. The absorption cross sections of the Co²⁺ ion in the GGG crystal at a wavelength of 1535 nm are determined for transitions from the ground (σ_gs = 4.8 × 10^-20 cm²) and metastable states (σ_es = 1.4 × 10^-20 cm²). Preliminary experimental results on Q-switching of erbium laser radiation by a Co²⁺:GGG passive Q-switch are presented.

The features of the pump dynamics of isomeric nuclei excited by X-rays of a repetitively pulsed relativistic electron beam followed by the production of a medium with the negative absorption of gamma quanta are analysed. In the extended nuclear medium, the pump excites a travelling hidden-population-inversion wave with the anisotropic gamma amplification, which becomes positive in the case of the excess over the critical pump parameter equal to the product of the peak spectral power density of the X-ray source and the relative duration of an ultrashort relativistic electron bunch. In the alternative scheme with orthogonal directions of pumping X-rays and a flux of amplified gamma quanta, the absence of the amplification anisotropy opens up the possibility for constructing a standard two-mirror resonator with Bragg single-crystal reflectors. The critical peak value of the spectral pump power density is compared with the known characteristics of relativistic-electron X-ray sources by examples of some nuclides.

The lensing effects in diode end-pumped Yb:YAG laser rods and discs are studied. Two mechanisms of refractive-index changes are taken into account, thermal and electronic (due to the difference between the excited- and ground-state Yb³⁺ polarisabilities), as well as pump-induced deformation of the laser crystal. Under pulsed pumping, the electronic lensing effect prevails over the thermal one in both rods and discs. In rods pumped by a highly focused cw beam, the dioptric power of the electronic lens exceeds that of the thermal lens, whereas in discs steady-state lensing is predominantly due to the thermal mechanism.

The peculiarities of the effective cubic nonlinearity are analysed upon second harmonic generation in a medium with a quadratic nonlinearity. It is shown that in this case, the polarisation state of the pump wave changes during its propagation due to additional effective photoinduced anisotropy of propagation constants of two orthogonally polarised pump components. Depending on the initial conditions, either an elliptically polarised cnoidal wave is produced (the polarisation state of pump radiation periodically changes from linear to elliptic and vice versa) or a passage occurs to an aperiodic polarisation 'chaos'.

Amplification of probe radiation by an inversionless two-level system in the 'red' wing of its spectral line is studied theoretically during the resonance absorption of intense cw laser radiation. The effect is caused by the inequality of the spectral densities of the Einstein coefficients for absorption and stimulated emission outside the absorption line under conditions when homogeneous broadening, due to the interaction of particles with the buffer gas, significantly exceeds the natural broadening (at high pressures of the buffer gas). It is found that the larger the inversionless gain, the higher the buffer gas pressure and the pump radiation intensity. It is established that at high enough pump intensity, the probe field is amplified along the entire region of the 'red' wing of the line (at any negative detunings of the probe field frequency).

A loop SBS oscillator is studied, in which pump radiation coupled out from a nonlinear medium is directed backward to the medium. To increase the interaction length, a light guide is used. The feedback is obtained on a stationary nonlinear refractive index grating produced by the pump waves. The signal generated at the Stokes frequency in the loop propagates in the direction opposite to the pump and is amplified due to the classical backward SBS. Such an oscillator can be treated as a distributed feedback oscillator produced by the pump waves themselves.

Main restrictions in the realisation of multipass unstable resonators caused by intracavity losses and large-scale aberrations are considered. The influence of intracavity losses on the laser radiation power and divergence is analysed based on the numerical simulation of an unstable resonator. The efficiency criterion for the unstable multipass resonator is proposed, which is proportional to the radiation brightness and takes into account the influence of the misalignment, thermal deformation and the main parameters of the active medium and resonator on the parameters of laser radiation.

Two-dimensional Bragg resonators with the coupling of TE- and TM-polarised waves are proposed. The selective properties of such resonators are analysed. Within the semiclassical approach, the nonlinear dynamics of laser radiation with a two-dimensional (in the xy plane) distributed feedback is studied, at which TE-polarised waves, propagating in the ±z directions, are amplified in the active medium (in particular, based on quantum wells). The latter, on a two-dimensional Bragg structure, are scattered into TM-polarised waves propagating in the ±x directions. These partial wave flows do not interact with the active medium but provide the spatial radiation synchronisation. The conditions of the solution self-similarity are obtained with increasing the dimensions of the active medium and the corresponding increase in the integral output power. It is shown that when an additional end mirror is mounted, almost unidirectional radiation coupling can be realised.

An original microcavity array IR photodetector is proposed and the sensitivity and response time of its pixels are calculated. A photosensitive element represents a composite silicon microcavity made of two optically coupled closed waveguides on a dielectric substrate whose resonance wave depends on its temperature. This dependence is used to detect IR radiation which heats an absorbing element and the composite microcavity thermally coupled with this element. It is shown that for a spatial resolution of 45 μm, the time response is 30 ms and the sensitivity is 10^-3 K at the IR radiation power of ∼ 4.7 × 10^-8 W element^-1.

New wide single-mode strip and grating loaded (SGL) channel waveguides made of silicon nitride on the oxide buffer layer of a planar silicon-on-insulator waveguide are studied. The central 10-lm-wide strip produces a multi-mode channel waveguide and diffraction gratings with a period 0.6 lm built on the structure edges produce mode-dependent additional losses due to radiation to the surrounding medium. The optical properties of these waveguides are discussed using the results of a three-dimensional numerical simulation by the FDTD and BPM methods. It is shown that a wide SGL waveguide is quasi-single-mode one because ithas a small propagation loss (∼ 0.3 dB cm^-1) for the fundamental mode and a high (up to -20 dB cm^-1) loss forthe higher order modes. The new SGL waveguides are CMOS compatible and can become basic for fabricating new photonic elements, including tunable optical filters and multi-plexers based on the multireflector technology.

This work examines reflection of a light wave from the surface of a semi-infinite medium covered with an ordered monolayer of spherical nanoparticles. We derive analytical expressions for the electric fields within and outside such structures with allowance for the electrodynamic interaction of the nanoparticles with one another and with the substrate. It is shown that such metalayers may raise or reduce the reflection coefficient relative to Fresnel reflection from an uncoated substrate surface. Constructive and destructive interference conditions are examined. We derive and analyse a zero-reflection condition in the form of a relationship between the parameters of the monolayer and medium.