Table of contents

The propagation of a narrow-band signal (wave packet) in a medium with population inversion is considered. It is shown that in an optically thick medium layer the signal decomposes into the initial and amplified signals propagating at different velocities and having different durations. The initial signal propagates without distortions at the velocity c/n₀ (n₀ is the refractive index of the medium away from the resonance frequency) and plays the role of a precursor of the amplified signal. The amplified signal moves at a lower velocity. It lags behind the initial signal during propagation and acquires a universal Gaussian shape (irrespective of the shape of the initial signal and the spectral line profile). The appearance of the amplified signal, which substantially differs from the initial signal in all the parameters, as well as the interference between the amplified and initial signals looks like a 'extra-distortion' of the initial signal.

The use of a self-filtering cavity in a laser makes it possible to obtain a high-quality high-power output beams. A maximum output power of 8.3 kW with an electrooptical efficiency of 11.3% is obtained. Estimates show that a high-quality beam with power up to 20 kW can be generated in electric-discharge CO₂ lasers with a self-filtering cavity.

A diode-pumped self-Q-switched erbium-doped fibre laser is developed and studied. The laser has an all-fibre configuration containing a piece of an active heavily erbium-doped fibre and two fibre Bragg grating mirrors and does not require any additional intracavity elements to obtain short pulses. Analysis of the laser operation suggests that the most probable mechanism of passive Q-switching of the laser cavity is absorption from the excited state of erbium resulting in the thermally induced nonlinear change in the refractive index in the erbium-doped fibre.

The spectral-threshold characteristics of a distributed-feedback (DFB) laser with the sinusoidal modulation of the complex coupling coefficient are studied within the framework of the linear theory of coupled modes. The analysis is performed in a broad range of amplitudes of the coupling coefficient for phase, amplitude, and amplitude — phase gratings providing distributed feedback in the active medium of the laser. It is shown that the eigenmode spectrum of the DFB laser on a phase grating with a large-scale modulation of the coupling coefficient is similar to the eigenmode spectrum of the DFB laser on an amplitude grating with a constant coupling coefficient. The DFB laser under study is promising for obtaining stable single-frequency lasing and can find applications in devices in integrated optics.

The spectral characteristics of efficient nonchain HF and DF chemical lasers are studied. It is found that the emission spectra of nonchain lasers operating with high efficiency are strongly broadened. Almost 30 emission lines of an HF laser and cascade lasing on the v(3-2) → v(2-1) → v(1-0) vibrational transitions of HF molecules for a number of rotational lines are obtained. It is shown that the development of discharge inhomogeneities significantly reduces the number of lasing lines in the spectra of nonchain chemical lasers. For an SF₆ — D₂ mixture excited by a generator with an inductive storage, about 40 lasing lines are observed on four vibrational transitions of DF molecules and the v(4-3) → v(3-2) → v(2-1) → v(1-0) cascade lasing is obtained at several rotational lines. Nonchain HF and DF electric-discharge lasers with a total and intrinsic efficiency of up to 6% and 10%, respectively, pumped from capacitive and inductive generators are developed.

It is found experimentally that the application of a magnetic field to the active element of a monolithic ring Nd:YAG chip laser in nonstationary lasing regimes can result in nonidentical spectral parameters of counterpropagating radiation waves (spectral nonreciprocity) in quasi-periodic and chaotic lasing regimes. The value of the spectral nonreciprocity depends on the coupling coefficient of counterpropagating waves, the excess over the pump threshold, and the optical nonreciprocity of the ring cavity. The obtained results are in good agreement with the results of numerical simulation.

The peculiarities of nonlinear dynamics of solid-state bidirectional ring Nd:YAG chip lasers are studied theoretically and experimentally during periodic modulation of mechanical stresses in the active element. It is shown that modulation of mechanical stresses is an effective method for exciting dynamic chaos in a monolithic chip laser.

Industrial CO₂ lasers of various types with stable cavities, which contain deformable mirrors with a controllable curvature of the reflecting surface, are studied experimentally. Stable and reproducible control of the output power of industrial CO₂ lasers is achieved in both single-mode and multimode regimes until the complete lasing quenching. Stable repetitively pulsed lasing regimes with a pulse repetition rate varied from a few to several hundred hertz are obtained in cw CO₂ lasers. The shapes of the output laser pulses and the dependence of the mean output power on the frequency — time parameters of the control voltage applied to the intracavity deformable mirror are studied.

A system is developed which allows one to stabilise the diode laser frequency at any point in the vicinity of the cyclic D₂-line transition in Rb in the interval from +40 to -150 MHz and to switch the laser frequency within this interval for ∼1 ms. A method is proposed and realised for increasing the contrast of the reference sub-Doppler resonance observed in circularly polarised fields. The ultimate contrast of the resonance is estimated. This system can be used to study the anomalous light pressure force acting on atoms in an optical molasses. A magnetooptical trap for Rb atoms is described.

The mechanism of supercontinuum generation and the spatial distribution of its sources during the propagation of a high-power femtosecond laser pulse in liquids and gases are studied. The numerical simulation shows that the supercontinuum is generated due to self-phase modulation of the laser pulse in space and time in the presence of nonlinearity and wave effects. Supercontinuum sources are found to be located mainly in the ring structure of the laser pulse at the intensity minima. It is established that the efficiency of generation of the short-wavelength part of the supercontinuum during the propagation of the focused laser beam depends on the initial phase modulation and achieves a maximum when the compression length slightly exceeds the length of nonlinear focusing.

A system consisting of two thin films interacting resonantly with a light field is considered. The model formulated for such a system is based on the approximation of two-level atoms and takes into account the peculiarities of the semiconductor medium, in particular, the effect of the ratio of dispersions of real and imaginary parts of the susceptibility (α-factor). It is shown that the inclusion of the α-factor leads to an additional nonlinearity and a considerable modification of the set of steady states of the system. The effect of α-factor on the dynamic regimes emerging in the system is discussed.

The spatial distribution of monochromatic light fields is studied in a tapered silicon fibre with the subwavelength aperture. The lowest-order electric TM₀₁ mode is analysed theoretically in a cone with perfectly reflecting metal walls filled with a light absorbing medium. Exact formulas and approximate expressions are obtained for a medium with the complex permittivity, which describe the spatial dependences of the electric and magnetic energy densities inside the cone. The behaviour of the field at the waveguide exit is analysed for the aperture diameter as small as ∼1/30 of the wavelength. The main attention is devoted to the transmission coefficients of the probe, which were calculated for a wide range of its geometrical parameters in the wavelength region from 400 to 830 nm. It is found that silicon provides a substantial increase in the output light energy density at the optical probe end both in the IR and visible spectral regions compared to glass.

Propagation of light in a circular system of coupled waveguides is studied. The system of cylindrical waveguides is constructed with the help of SPCVD technology used for synthesising optical fibre preforms. It is shown that a 0.63-μm light beam focused at the entrance of a cylindrical system propagates in it with radiation power losses. The radiation is spatially modulated, which makes possible to estimate the period of beam width oscillations inside the waveguide system.

The effect of IR and UV laser pulses on thin metal and composite films on glass substrates as a function of the energy density is studied. Upon irradiation by ∼300-ns laser pulses with a nonuniform energy-density distribution over the laser-beam cross section, the characteristic regions can be distinguished on the film surface. The dimensions of these regions correlate with the energy distribution in the beam and correspond to the evaporation, melting, and damage conditions caused by thermal stresses. For a uniform energy-density distribution over the laser-beam cross section and a pulse duration of ∼20 ns, the adhesion of metal and composite films to glass was disturbed due to induced thermal stresses without substrate melting. The threshold laser-energy densities required for disturbing the adhesion of titanium, titanium nitride, zirconium, niobium, and stainless-steel films on glass substrates are measured. Numerical estimates of the surface temperature and thermal stresses caused by heating show that the film adhesion to a substrate can be overcome by expending a small fraction of the energy, while most of the energy of thermal stresses goes to the formation of cracks and the kinetic energy of escaping film fragments. It is suggested to use pulsed laser radiation to roughly estimate the adhesion of metal and composite films to glass substrates.

A wide-aperture Pockels cell based on a DKDP crystal having an optical diameter of 70 mm is studied. Three silver ring electrodes deposited on the side surface of the crystal were used to apply a high-voltage rectangular pulse of variable duration from 50 to 150 ns to the cell. Chains of KT6117A (2N5551) transistors operating in the avalanche regime served as fast electron switches. The duration of the leading and trailing edges of the pulse formed by these switches did not exceed 15 ns. The nonuniformity of the transmission coefficient over the cross section of the cell caused by the inhomogeneity of the electric field inside the crystal was close to 3.5%.

Cooperative sensitisation of luminescence of Nd³⁺ ions at the ⁴F_3/2 → ⁴I_13/2, ⁴I_9/2 transitions by Pr³⁺ ions was observed in a borate glass doped with Pr³⁺—Nd³⁺ ion pairs. The luminescence was excited by a 800-mW, 1.064-μm Nd³⁺:YAG laser. Simultaneously, spontaneous Raman scattering was observed in glasses containing Pr³⁺—Nd³⁺ ion pairs or only Pr³⁺ ions. The Stokes shift from the 9398-cm⁻¹ excitation line is 794 cm⁻¹. The mechanism of nonradiative energy transfer is discussed.

Expressions are obtained for calculating the four first coefficients of a polynomial model of the frequency characteristic of a slowly rotating laser gyro on a vibration stage. The expressions are valid when the gyro operates at the gain line centre and currents in its arms are balanced, however, the amplifications of counterpropagating waves are slightly different due to slightly different Q factors of the resonator for these waves. Analysis of the expressions suggests that the difference in the amplification of counterpropagating waves of the laser gyro leads to the zero shift and produces the component of the output signal that does not commute with the angular velocity.