Table of contents

The properties of frequency conversion of Bessel light beams (BLBs) in nonlinear crystals are studied theoretically and experimentally. New possibilities and prospects of the development of methods for nonlinear optical frequency conversion using BLBs are discussed. The second harmonic generation (SHG) is studied under the conditions of critical and noncritical phase matching. The longitudinal and transverse phase matching is analysed in detail upon SHG and sum frequency generation in BLBs. The concept of azimuthal width of phase matching caused by the longitudinal and transverse wave detuning is introduced, and its value is calculated for collinear and π-vector interactions. The regime of azimuthally matched interactions is selected, which is realised when the azimuthal phase matching width is small. A correlation of the azimuthal BLB components caused by these interactions is predicted. It is shown that azimuthally matched BLBs are characterised by a significant increase in the overlap integral and by nonlinear interactions that do not destroy their spatial structure.

The influence of cerium oxide on photo- and gamma-stability of chromium-ytterbium-erbium phosphate glasses is studied. It is found that UV irradiation does not cause any noticeable changes in the glass independently of the presence of cerium. Gamma rays produce colour centres in glasses without cerium and their lasing properties deteriorate. Doping glasses with an optimum amount of cerium oxide improves their radiation resistance with respect to gamma rays.

Characteristics of a pulsed, multifrequency electroionisation CO laser operating on the first vibrational overtone of the CO molecule are studied experimentally and theoretically. It is shown experimentally that a pulsed, multifrequency overtone CO laser is an efficient source of coherent radiation in the 2.5–4.1-μm region whose specific output reaches 50 J l^-1 amagat^-1 and the electro-optical efficiency amounts to 11 %. A theoretical analysis based on experimental data shows the feasibility of obtaining overtone emission with efficiency as high as ~20 %. The alternation of the intensity of vibrational bands in the overtone CO laser is discussed. This effect is caused by the cascade mechanism of formation of the emission spectrum. The comparison of experimental data with calculations showed that they agree well with respect to spectral and energy characteristics of the overtone CO laser. Moreover, it revealed the necessity of refinement of the kinetic model of the active medium of the CO laser for obtaining an adequate description of time parameters of a laser pulse.

The output characteristics of a two-colour Nd³⁺:YAG laser with a dispersive cavity, emitting at 1.32 and 1.06 μm, are considered. The enlargement of the region of stable two-colour lasing, due to the reduced competition in the case of spatially separated channels, is demonstrated. The influence of the size of the pumped region on the laser efficiency and the competition between the lasing channels is studied. It is shown that, in the case of a single pump source, the weakening of the competition between the waves is accompanied by a reduction in the laser efficiency. A novel construction of the two-channel laser with two pump sources is proposed, which offers increased stability without the reduction in the efficiency.

An experimental investigation was made of the principal factors that determine the possibility to increase pulse repetition rates in high-power KrF lasers. Two prototypes of a compact industrial KrF laser were considered. The first one produces a maximum average output power of ~620 W for a pulse repetition rate of 4 kHz; the second, a more compact prototype, yields a maximum pulse repetition rate of 5 kHz for an average output of 200 W.

The dynamics of oscillation in a solid-state laser with intracavity second-harmonic generation under the influence of an external signal at the second-harmonic frequency injected into its cavity in the presence of feedback at the double frequency is theoretically studied. Boundaries of the regions of injection locking for three stationary laser states differing in the nonlinear phase incursion caused by radiation conversion into the second harmonic are found. Relaxation oscillations in the stationary state of injection locking are studied. It is shown that the second relaxation frequency, which is related to phase perturbations of the second harmonic and perturbations of the phase difference of waves in a nonlinear crystal, is excited in a single-mode solid-state laser in addition to the fundamental frequency of relaxation oscillations. Conditions are found under which relaxation oscillations at the second relaxation frequency are excited.

A set of diode-pumped fibre lasers producing a cw output of 4–7.5 W in the range from 1.05 to 1.15-μm is realised on the basis of an ytterbium double-cladded fibre. The output of the ytterbium fibre laser was used to pump a Raman phosphor-silicate fibre converter, resulting in fibre lasers producing a cw output power of more than 3 W at 1.26 and 1.3-μm.

Using a FM Gaussian pulse travelling in a two-mode periodic optical fibre as an example, it is shown that dispersion parameters caused by the complexity of the refractive index substantially affect the pulse dynamics. In particular, the imaginary part of the effective dispersion enables one to compress a pulse in an amplifying medium without its initial frequency modulation.

It is shown that a spectral gain line narrows down and its profile is normalised with increasing optical thickness of a layer of the amplifying medium. As a result, the gain line profile always becomes Gaussian, independently of the true form factor of the line, when the thickness of the active medium layer is sufficiently large. The normalisation of the line profile is demonstrated for the lines with Lorentzian, Gaussian, and 'time-of-flight' profiles.

The effect of a regular phase modulation on the dynamics of variation in spatial characteristics of laser radiation is studied. The conditions and processes of the transformation of phase aberrations to topological wavefront perturbations resulting in the appearance of edge and screw dislocations are considered. The relationship between the caustic and dislocation elements of the laser beam is discussed. It is shown that the phase modulation leads to the formation of narrow channels with an increased intensity inside the laser beam.

Experimental and theoretical study of locking of two mutually orthogonal polarisation modes in a cw flashlamp-pumped Nd³⁺:YAG laser is reported. The possibility of locking polarisation modes by a radio signal is shown theoretically. The limiting detuning allowing for the existence of locking is determined. Locking at 23 MHz is experimentally studied.

A method for controlling the refractive index that is based on the backward rescattering of the scattered and amplified electromagnetic waves is proposed and analysed. The resulting field is a sum of the initial (probe) wave and the rescattered wave. The effective wave number of the total wave can be varied by varying the gain. This variation in the wave number can be treated as a variation in the refractive index, although the physical properties of the medium do not change. The effective refractive index for the total wave propagating in such a device was called the virtual refractive index.

Single-mode optical fibres were fabricated from a germanosilicate glass by the method of modified chemical vapour deposition (MCVD), which used sintering of a porous glass in a reducing (helium or nitrogen-containing) atmosphere. The optical fibres exhibit a high photoinduced change in the refractive index and a high efficiency of recording quadratic nonlinear susceptibility compared to a standard germanosilicate fibre. Sintering, both in nitrogen and in helium atmospheres, was shown to increase the concentration of germanium oxygen-deficient centres in glass. It is likely that nitrogen enters into a germanosilicate glass in the concentration that is sufficient to modify the glass structure and to additionally increase its photosensitivity. The replacement of oxygen or silicon in the close vicinity of an oxygen vacancy by nitrogen may play a key role in the photosensitivity enhancement owing to the formation of additional valence bonds and blocking of recombination processes.

The nonlinear dynamics of an open quantum system containing an arbitrary number of two-level atoms coupled with a classical polychromatic electromagnetic field and a quantised mode of the electromagnetic field is studied. Two particular cases of the elastic and inelastic interactions are considered. In the first case, the quantised mode is resonant with the transition between the quasi-energy levels corresponding to the same quasi-energy state, while in the second case, the levels involved in the interaction correspond to different quasi-energy states. For the elastic interaction, which can appear only in open quantum systems, an analytic solution of the Heisenberg equations is obtained. The time dependences of the population of quasi-energy states, the number of photons in the quantised mode, and photon statistics are numerically analysed for the inelastic interaction and at the crossing point of quasi-levels, when both types of the interaction are simultaneously present.

A simple analytical technique, based on the Babinet principle, for calculating low diffraction losses of different kinds in stable resonators is described. The technique was verified by comparison with the known numerical and analytical calculations of the losses in specific diffraction problems.

The results of a theoretical investigation of the efficiency of degassing of the near-surface region of a material exposed to laser radiation are presented. The case of a low volume concentration of the monodispersed gas phase representing microbubbles of size no greater than 10 μm is considered. The principal parameters are revealed which determine the regimes of the egress of gas bubbles from a laser-produced melt, and analytical formulas are obtained for estimating the process rate. The analytical results are compared with the results of two-dimensional numerical simulations which include the laser heating of a solid sample, its melting, the development of thermocapillary melt convection, and the escape of gas bubbles from the melt. The analytical and numerical results are found to be in good agreement.

A laser receiver (LR) with an active quantum filter (AQF) (λ =1.315 μm) based on an iodine photodissociation laser is studied. It is shown that the LR sensitivity can be brought up to the quantum detection limit by increasing the AQF gain. Taking into account the space-time statistics of spontaneous emission of the AQF, the LR sensitivity is determined as a function of the reception solid angle and the recorder response time. Under the conditions of the experiments performed, the LR sensitivity is, to a good approximation, proportional to the square root of the product of the reception solid angle and the recorder time constant. The above dependence is confirmed experimentally upon more than a hundred-fold variation of the response time. For the reception angle that was three times greater than the diffraction-limited angle, the quantum detection limit was achieved, which amounts to approximately three photons for a 40-ns pulse for the unit signal-to-noise ratio.

An analysis is made of a lidar designed on the basis of a broadband repetitively pulsed IR parametric oscillator for monitoring multicomponent aerosol and gaseous atmospheric pollutions. It is shown that efficient parametric generation of femtosecond IR radiation can be obtained in a scheme using the properties of group velocity matching.

The possibility of using photonic crystals with a lattice defect for the laser guiding of cold atoms is analysed. We have found a configuration of a photonic-crystal lattice and a defect ensuring the distribution of a potential in the defect mode of the photonic crystal allowing the guiding of cold atoms along the defect due to the dipole force acting on atoms. Based on quantitative estimates, we have demonstrated that photonic crystals with a lattice defect permit the guiding of atoms with much higher transverse temperatures and a much higher transverse localisation degree than in the case of hollow-core fibres.