Table of contents

Diode-pumped lasers based on mixed Nd:Gd_0.7Y_0.3VO₄ vanadate crystals are studied. Continuous-wave lasing with the slope efficiency of 71% and the average output power up to 8.2 W is obtained. Active mode locking with an acousto-optic modulator, passive mode locking by the Kerr nonlinearity, and hybrid mode locking are investigated. Picosecond laser pulses of duration 1.7 ps are obtained at an average output power of 340 mW and a pulse repetition rate of 140 MHz.

The parameters of laser radiation and kinetic processes of plasma formation and production of inverse population are studied. Electrophysical processes proceeding in a feed circuit containing a semiconductor opening switch and intermediate inductive energy storage are also considered. It is shown that the semiconductor opening switch controls the amount of energy in the inductive storage, and a high-voltage short prepulse with a peak pump power density of ∼1 MW cm^-3 appearing during the current interruption can produce a volume-discharge plasma and create the inverse population for the time ∼10 ns, providing the conditions for efficient pumping of the active medium from the main capacitor. The time dependences of the pump and emission powers, the concentrations of electrons, excited xenon atoms, HCl(v) molecules in excited vibrational states and of the ionisation, recombination, and attachment rates are calculated. Kinetic processes determining the parameters of laser radiation are analysed. The output energy up to 1.0 J is obtained for 90-ns (FWHM) pulses with the efficiency up to 4.0% with respect to the pump energy. The maximum output power was 11 MW for the lasing efficiency of 4.7% with respect to the pump power. The calculated and experimental time dependences of the voltage across the laser gap, discharge current, and output power are in good agreement.

The design of a copper chloride laser is described, and the laser is optimised by studying the dependence of its output power on the buffer gas type. The voltage and current of the laser discharge at the optimum buffer gas pressure are measured. The influence of the diaphragm diameter on the specific output power is studied after optimisation of switch parameters. When an diaphragm producing the optimal temperature gradient in the laser gas-discharge tube, the record specific output power of 123 W L^-1 is obtained without any admixtures.

It is shown that optimisation of the structure of the active channel of quantum-dot InAs/AlGaAs/GaAs superluminescent diodes (SLDs) provides a noticeable increase in their external quantum efficiency. The output cw power coupled out of a single-mode fibre achieves 1.3 and 0.9 W for the emission bandwidth of 27 and 110 nm, respectively. The results of preliminary lifetime tests predict the high enough reliability of these SLDs.

The energy and time characteristics of a passively Q-switched Nd³⁺:YAG laser with a Cr⁴⁺:YAG Q switch emitting pulse trains are studied and analysed theoretically. The description and technical parameters of a small autonomous laser with intracavity second-harmonic generation (ICSHG) in the pulse-train regime are presented. The laser provides a high total pulse-train energy for a relatively low peak power of a single pulse, stable operation in a wide temperature range, and has a small weight and size, which is convenient in operation. The enhanced reliability and stability of the laser operation are provided by its original technical design: the ICSHG scheme for type II phase matching without polarisers, the use of temperature-noncritical phase matching in KTP crystals, dust- and moisture-proof casing, and battery-operated pulsed power supply for the pump flashlamp.

The regime of polarisation switching in a double-clad ytterbium fibre laser is studied experimentally and explained theoretically. It is shown that polarisation switching appears in lasers with the long active medium (no less than 20 m) when the pump slightly exceeds the threshold. The experimentally observed properties of spontaneous polarisation switching in the ytterbium fibre laser are explained by the competition of modes with orthogonal polarisations taking into account the polarisation-dependent saturation of amplification and losses.

A multimode cladding-pumped erbium-doped fibre laser is described. The maximum output power and the slope efficiency of the laser at 1.6 μm are 4.2 W and 30%, respectively.

The type of coupling in a fibre laser array phase locked with the help of an external mirror located at the focal distance from the plane of output ends of individual lasers is studied analytically. The explicit expression is derived for the eigenvalue of the resonator and the restriction on the width of the tuning range in which laser array phase locking is preserved is determined. The influence of the spread in the optical lengths of fibres on the phase-locking efficiency is considered. The phase-locking efficiency is analysed for the spread of optical lengths of fibres considerably exceeding the radiation wavelength.

The passive Q-switching of 1.66-μm Er³⁺:YAlO₃ lasers with the help of some saturable absorbers is studied. Giant 200-ns pulses are generated by using a Cr²⁺:ZnSe crystal as a saturable absorber.

The self-focusing of two-dimensional Gaussian beams in cubic photorefractive optically active crystals of the (0) cut in the external electric field arbitrarily oriented in the cut plane is theoretically studied. The ranges of orientation of the external electric field are found in which the divergence of the light beam is smaller than the diffraction divergence. The dependences illustrating the existence of two-dimensional spatial solitons in a 15-mm-thick Bi₁₂SiO₂₀ crystal are constructed taking into account the optical activity or neglecting it. The shape of a light beam propagating in the crystal is determined.

The possibility of amplification of difference terahertz-frequency signals generated in one-dimensional nonlinear crystals is studied theoretically. It is shown that the intensity of nonlinear terahertz signals can be considerably increased both due to the coherent summation of waves generated in several photonic crystals and the choice of a special configuration of photonic crystals representing a two-periodic structure.

An efficient Q-switched optical parametric HgGa₂S₄ crystal oscillator pumped by a Nd:YAG laser is developed. The oscillator can be continuously tuned in the region from 3.7 to 5.7 μm. The average output power at 4 μm was 67 mW for a pulse repetition rate of 20 Hz. The energy conversion efficiency achieved 4.9%.

The formation efficiency of fractal nanostructures is studied experimentally depending on the composition of the binary silicon–silica mixture during evaporation by millisecond laser pulse. The influence of percolation on the efficiency of nanostructure formation in a laser plume is discovered. It is found that the efficiency is maximal near the critical densities of atoms in the plasma, which correspond both to the three-dimensional and two-dimensional percolation. The dependences of the effective temperatures of the laser plasma and the intensity of spectral lines on the target composition are presented.

The results of spectral calculations of the dynamics of laser radiation absorption and X-ray generation in a spherical box converter are presented for experiments on inertial fusion performed in the 1990s on the Iskra-5 facility. Numerical simulations were carried out taking into account the actual configuration of 12 laser beams and six apertures for introducing laser radiation. Calculations were performed in the sector approximation in which the inner surface of the box is divided into a certain number of regions or sectors. The movement of matter and radiation transport in each sector were calculated by using the one-dimensional spectral nonequilibrium dynamics program. Spectral calculations showed a strong inhomogeneity of irradiation of a capsule in the M-band region (2.7–2.9 keV). It is shown that the spectrum-averaged root-mean-square inhomogeneity of the X-ray energy flux on the capsule (during the time of its compression) is about 2.5% for laser beams of the same energy and is about 3% if the characteristic energy misbalance between the beams is taken into account.

The possibility of energy transfer over long distances in the form of laser radiation propagating in dielectric optical fibres is discussed. Because nonlinear-optical phenomena in glasses prevent the transfer of high radiation powers in standard two-layer fibres, the outlook for this transfer is associated with the development of the technology of microstructure fibres with a hollow core and with further progress in the development of high-power fibre lasers.

Single-mode crystalline optical fibres for transmitting the 10.6 μm CO₂ laser radiation with optical losses 4–5 dBm^-1 are fabricated for the first time.

A single-mode microstructured fibre for the mid-IR region based on silver halide crystals is fabricated for the first time. It is shown theoretically and experimentally that the fibre is virtually single-mode at a wavelength of 10.27 μm and has optical losses equal to 2 dBm^-1. It is demonstrated that crystal microstructured fibres offer a number of advantages compared to common fibres made of silver halide crystals. A broad transparency window of these materials (2–20 μm) makes promising the use of these fibres in spectroscopy and in nonlinear fibre devices for the mid-IR region.

The photoinduced room-temperature-stable increase in the refractive index by ∼5×10^-4 at a wavelength of 1.55 μm was observed in phosphosilicate fibres without their preliminary loading with molecular hydrogen. It is shown that irradiation of preliminary hydrogen-loaded fibres by an ArF laser at 193 nm enhances the efficiency of refractive-index induction by an order of magnitude. The induced-absorption spectra of preforms with a phosphosilicate glass core and optical fibres fabricated from them are studied in a broad spectral range from 150 to 5000 nm. The intense induced-absorption band (∼800 cm^-1) at 180 nm is found, which strongly affects the formation of the induced refractive index. The quantum-chemical model of a defect related to this band is proposed.

The results of numerical simulation of acousto-optic (AO) tunable filters of a new type based on multireflection beam expanding in waveguide structures are discussed. Planar waveguide filters based on thin chalcogenide (As₂S₃) films of lithium niobate (LiNbO₃) are considered. The operation of filters is analysed by the finite-difference time-domain (FDTD) method by using the license FullWAVE software package (RSoft Design Group, Inc.). It is shown that AO filters have very good dispersion properties and AO filters of extremely small size provide a narrow filtration line within the tuning range of more than 100 nm (at a wavelength of 1.54 μm). It is important that the normalised linewidth (measured in units of the reciprocal filter length) is an order of magnitude smaller than the theoretical limit for AO filters produced from the same material in the conventional way, without the use of multireflection beam expanding.

A special type of modulation of the injection current of a diode laser is proposed at which the frequency modulation of radiation is not accompanied by the residual amplitude modulation. This method considerably reduces the influence of the diode laser radiation instability on the recorded absorption spectra. This allows a prolonged monitoring of small amounts of impurities in gas analysis by retaining a high sensitivity. Prolonged measurements of absorption spectra are performed at a relative absorption of 8×10^-7. By using a 50-cm multipass cell with the optical length of 90 m, the absorption coefficient of 1.2×10^-10 cm^-1 was detected. As an example, the day evolution of the background concentrations of NO₂ molecules was measured in the atmosphere.

A one-dimensional analytic hydrodynamic model of the direct laser-induced transfer of matter is considered. The efficiency of pulsed laser radiation energy conversion to the kinetic energy of the ejected matter is determined. It is shown that the hydrodynamic efficiency of the process for the layers of matter of thickness exceeding the laser radiation absorption depth is determined by the adiabatic index of the evaporated matter.