Table of contents

An analysis is made of a new possibility of constructing a source of intense optical radiation with easily controlled quantum-statistical characteristics. The source is based on the interference between light waves that have passed through an anisotropic medium having a cubic nonlinearity. The role of the self-interaction and cross-interaction effects in the generation of light with nonclassical properties is identified.

New types of miniature solid-state lasers with active elements in the form of micron-thick single-crystal ribbons and sheets activated with lanthanide and transition-metal ions are proposed. It is reported that the first crystal used for this purpose was orthorhombic KY(MoO₄)₂:Nd³⁺, lasing at room temperature as a result of the ⁴E_3/2 → ⁴I_11/2 transition when pumped with flashlamps or with lasers.

The operating principles, threshold characteristics, and physical factors imposing restrictions on the main operational parameters are reviewed for semiconductor lasers pumped by beams of accelerated electrons. The attention is focused on electrodynamics of the optical field and on the influence of the cavity configuration on the spectrum of the emitted modes. A brief account is given of the history of these lasers. The problems still not solved are discussed and potential ways of improving these lasers are considered.

Precision measurements and a comparative analysis were made of the emission spectra of GaAs/AIGaAs and InGaAs/GaAs heterostructure injection lasers with quantum-well active layers and plane—plane cleaved cavities. Attention was focused on the correlation between the linewidth enhancement factor and the parameters of single-frequency lasing. Single-frequency emission at λ = 975 nm was observed for a quantum-well laser with strained active layers and a cw output power in excess of 100 mW was reached when the side longitudinal modes were suppressed by more than 30 dB.

A method for coherent addition of the power of separate waveguide laser components by cascade connection of single-mode couplers is proposed. An experimental study is described of a laser system formed by two Nd³⁺-activated fibre lasers connected by X-type single-mode couplers. The efficiency of such radiation power addition is reported to be 95%.

The influence of small gamma-ray or electron doses on the output energy of Al₂O₃ : Cr³⁺ and YAG : Nd³⁺ lasers was investigated under 'passive' and 'active' conditions, i.e. in the absence or presence of lasing. The effects not observed at large doses were detected. The reasons for the experimentally observed phenomena were analysed.

An experimental investigation was made of the energy and spectral—time characteristics of an electric-discharge SF₆—H₂ laser. The spectral composition of the emitted radiation and its dynamics were studied as a function of the number of pulses in the absence of forced circulation of the active mixture. The technical efficiency was found to be 2.2% and the output radiation energy was 1.2 J.

Infrared-luminescence diagnostics, based on vibrational—rotational bands of the CO₂ molecule with the wavelengths 2.7 and 4.3 μm, was used in a study of the spatial structure of the characteristics of the active medium of an industrial fast-flow CO₂ laser excited by a self-sustained glow discharge with orthogonally sectioned electrodes. The distributions of the infrared luminescence intensity were determined along and across the gas flow in the gas-discharge chamber at various heights above the anode. The experimental infrared luminescence data were used to calculate the spatial distribution of the vibrational temperatures of the coupled and asymmetric modes of the CO₂ molecule in the downstream direction. The feasibility of monitoring the output power of an industrial laser on the basis of the 4.3 μm infrared luminescence band was demonstrated.

A calculation is reported of the reflection coefficients for degenerate four-wave mixing in thermal gratings that form in the active media of solid-state lasers. It is shown that these reflection coefficients may be close to the reflection coefficients of amplitude gratings in the active media of ruby crystal and neodymium glass lasers.

A method for controlling the frequency of radiation from a single-mode TEA CO₂ laser with external signal injection is proposed, justified, and has been realised experimentally. It allows the output frequency of the laser to be stabilised (to within ~0.1 MHz) during the time interval of maximum power, i.e. during the leading spike, by introducing a suitable nonlinear medium (InAs plate) into the laser cavity. The transition from a single-mode frequency-stable to a multimode lasing regime with regular and chaotic pulsations of the output power could occur because of internal injection excitation of adjacent transverse and longitudinal modes by radiation which was chirped due to the nonlinearity of the intracavity optical components even in the case of initially single-mode emission.

Theoretical and experimental investigations were made of the reaction of the laser power to an external radiation signal. The laser with an injected signal (LIS) was an He—Ne laser emitting radiation at the wavelength of 3.39 μm in the form of two orthogonally polarised modes. A study was made of the influence of the frequency detuning of the external signal from the LIS radiation, and also of the intensities of both radiations on the laser power response.

An investigation was made of some physicochemical ways of increasing the output radiation energy and the service life of a compact gas-discharge pulse-periodic excimer XeCl laser. The energy and the service life were enhanced by a change of the composition and of the temperature regime in working mixtures. For example, when boron chloride (BCl₃) was used as the halogen carrier, the energy of the output pulses increased by 20% and the service life was improved by 50%, compared with the traditionally used hydrogen chloride (HCl). Cooling of the working mixture of an XeCl laser approximately doubled the output energy and increased the service life to ~10⁶ pulses. The reasons for the improvement in the characteristics were the large rate constants of the formation of negative Cl^- ions in mixtures with BCl₃, fast accumulation of nonvolatile products in reactions of BCl₃ with impurities, and precipitation of aerosols on a heat exchanger in the gas channel.

Spatial distributions of laser radiation scattered by a laser spark were determined at different laser radiation wavelengths (λ = 1060, 530, 353, and 265 nm) and gas pressures (air at 10–760 Torr). An interference structure of the cone of the scattered radiation behind the spark was detected for the first time. The structure was attributed to interference of the radiation scattered in two or more self-focusing centres in the laser-spark plasma in air. The dependences of the maximum scattering angle on the gas pressure and on the laser radiation wavelength were determined experimentally.

A comparative analysis was made of the surface hardening of steel 45 by high-power CO₂ laser beams with a rectangular strip-like cross section and a traditional circular cross section. This was done under various conditions. The treatment with the strip-like beam ensured a higher homogeneity of the hardened layer and made it possible to increase the productivity by a factor of 2–4 compared with the treatment by a beam of the same power but with a circular cross section.

A dense jet of a plasma consisting of multiply charged ions was generated in the interaction of a laser plasma with a strong external axial magnetic field. Images were formed by spectral lines and the soft x-ray spectrum range of the plasma jet was obtained with a large-aperture spectrograph containing a mica crystal bent to form a spherical surface with a radius of R = 10 cm. A tenfold increase in the density of the He-like Mg XI plasma, compared with a freely expanding plasma, was observed at a distance of 5 mm from the target.

An analysis is made of the influence of the phase matching conditions on the four-photon scattering spectrum at a one-photon resonance under various focusing conditions. An analytic expression is obtained for the phase matching integral in the limiting cases of hard focusing and strong absorption in a medium with the cubic nonlinearity. A study is made of the influence of one-photon resonances on the form of the spectrum of four-photon scattering by excited and preionisation states of atoms. Calculations are reported of the four-photon scattering spectra in which allowance is made for the interference of the resonant and nonresonant components of the third-order nonlinear susceptibility. A method for the normalisation of the experimental four-photon scattering spectra under one-photon resonance conditions is proposed; this method allows for the distortions associated with the influence of the phase mismatch and of one-photon absorption.

An analysis is made of the feasibility of monitoring the efficiency of harmonic generation by an optical rectification signal which appears directly on the faces of an active nonlinear crystal during harmonic generation. An analysis is made of all possible uniaxial crystals from the point of view of feasibility of separation of the pump and harmonic contributions.