Table of contents

Small-signal gain (SSG) dynamics G(t) in the active medium of a pulsed laser amplifier operating on the v+1→vP(J) vibrational–rotational transitions of the CO molecule, including high (v > 15) vibrational transitions, is studied experimentally. It is demonstrated that as the vibrational number increases from 7 to 31, G changes with time slower, while G_max decreases in this case by three times. It is found that at a fixed value of v the rate of the SSG rise increases with increasing the rotational number J > 6. It is shown that in oxygen-containing gas mixtures (CO:O₂ = 1:19) the value of G_max at low vibrational levels (for v < 13) can substantially exceed G_max in mixtures containing nitrogen (CO:N₂ = 1:19) instead of oxygen. It is found that the efficiency (47%) of a CO laser on mixtures with a high concentration of oxygen considerably exceeds the efficiency (30%) of a CO laser operating on a nitrogen-containing mixture.

Efficient lasing is obtained in the visible and near-IR spectral regions in solutions of symmetric polymethine dyes of the indolenine series (indocyanines) pumped by the second harmonic of a Nd³⁺:YAG laser at 532 nm and an exciplex XeCl* laser at 308 nm into the first (long-wavelength) and higher-lying electronic absorption bands. The quantum lasing efficiency upon UV excitation achieves 37%. It is shown that these dyes can also limit the radiation power of these lasers. Polymethine dyes limit especially efficiently the second-harmonic power, their attenuation factor for the radiation power density of 100 MW cm^-2 achieving 14. The nanosecond flash-photolysis study of transient absorption spectra showed that the radiation power is limited by the mechanism of reverse saturated singlet–singlet absorption. It is established that the limiting ability of polymethines strongly depends on their structure.

A scheme of the system for pumping active gas media by electron beams injected into a gas volume located in a multipole magnetic field is proposed and engineering solutions are presented, which were used in the development and making of this system. The possibility of changing a resistance to a plasma current initiated by a relativistic electron beam is promising for the additional control of the kinetics of processes in the active gas medium with the aim of increasing the energy input efficiency. The scheme proposed in the paper allows the combination of the pumping of the gas medium by an electron beam with pumping by a controllable discharge initiated by this beam in electric fields of the beam. The energy input of electron beams to the gas medium located in a quadrupole magnetic field is analysed by the Monte-Carlo method. The calculations demonstrate a high efficiency (90%) of the beam energy transfer to the gas and the possibility to control the energy-input profile.

Repetitively pulsed lasing in a Yb, Er-doped phosphate glass transversely pumped by a diode laser array is studied. Lasing on the lowest TEM₀₀ resonator mode is obtained both in the quasi-continuous regime with an output power of 4.1 W and in the passive Q-switching regime (23-ns, 1.2-mJ pulses). The depolarisation of linearly polarised radiation of a He–Ne laser transmitted through the phosphate glass active element (AE) along the resonator axis is investigated. The dependences of depolarisation on the AE heating and experimental conditions are determined. It is shown that radiation losses caused by its depolarisation can present problems in the development of lasers emitting at 1.5 μm, in which polarisers should be used (for example, regenerative amplifiers).

A method for increasing the power of pulsed lasing on atomic and ion transitions in chemical elements obtained by the conversion of the UV radiation of excimer lasers in cells with metal vapours is studied. A part of UV radiation transmitted through a cell with metal vapour is used for pumping a dye solution in such a way that the cell converter with metal vapour represents a master oscillator, while the dye cell represents an amplifier. The study is performed by the example of amplification of weak spectral components of radiation from a XeCl* laser converted in mercury and barium vapours. In the amplifying stage the longitudinal pumping of the dye is used and a scheme for suppressing self-excitation is employed. It is found by selecting dyes that the alcohol solution of uranin is nearly optimal for amplification of the 546.1-nm laser line of mercury, while the best results in amplification of the 533-nm and 648.2-nm laser lines of barium were obtained by using alcohol solutions of rhodamine 6G and oxazine 17, respectively. The power of the 546.1-nm mercury line was increased by an order of magnitude, while the power of the 533-nm and 648.2-nm lines of barium – almost by a factor of twenty-five.

The effect of a constant magnetic field on the nonlinear radiation dynamics of a monolithic chip ring Nd:YAG laser pumped by modulated radiation is studied experimentally. It is found that the application of a constant magnetic field to the active element of the solid-state ring laser operating in the non-stationary regime results in the displacement of the regions of existence of quasi-periodic and chaotic lasing regimes to the low-frequency region of pump power modulation. In addition, the application of a magnetic field to the active element of the laser gives rise to the spectral nonreciprocity.

The conditions of phase locking of a three-channel holographic Nd:YAG laser system based on self-pumped phase-conjugate oscillators emitting giant 100-mJ, 60-ns monopulses in each of the channels are investigated experimentally. The pulse-to-pulse stable self-phase-locking of the laser system with a pulse repetition rate up to 20 Hz is obtained. The mutual coherence of laser channels was increased up to 0.87 by separating the controlling channel which initiates lasing in a set of controllable channels generating synchronous monopulses.

The properties of hybrid prism–grating dispersion systems are studied. The scheme of a prism–grating stretcher matched to a standard compressor in the phase dispersion up to the fourth order inclusive is developed for a petawatt laser complex based on the optical parametric chirped-pulse amplification. The stretcher was used to obtain the ∼200-TW peak power of laser radiation.

The appearance of the harmonic modulation regime at the Hopf bifurcation point is described analytically for a delayed-feedback semiconductor laser. The second-order delay differential equation with complex coefficients is derived. The frequency of oscillations appearing at the Hopf bifurcation point is determined by the solution of two relatively simple transcendental equations, from which the bifurcation point itself is found. These equations contain dependences on all the control parameters of the problem. The exact upper and lower limits of the oscillation frequency are found. A comparison with numerical results shows that the modulation frequency is preserved almost constant in a broad range of feedback phases. A procedure is proposed for determining the parameters of the laser providing the presence of bifurcations with a passage to oscillations with the specified frequency. The results obtained in the paper are of interest for WDM communication systems.

The exact solution of nonlinear equations describing the symmetric stationary interaction of two light waves of an arbitrary polarisation on a local photorefractive grating in a crystal of the symmetry group 3m in the transverse configuration of crystal faces is obtained in the paraxial limit. The polarisation of light waves and efficiency of energy transfer between them are studied as functions of the reduced length of a sample and the intensity ratio of incident waves.

Cubic boron nitride (cBN) – a kind of an artificial (synthetic) crystal with the band gap of ∼6.3 eV, which has the zinc blende structure and the 3m symmetry, is studied. The optical rectification is obtained and the second harmonic generation (SHG) is observed in the cBN crystal for the first time by using a 1064-nm Q-switched Nd:YAG laser. The green light at 532 nm from the cBN sample can be seen with a naked eye.

It is shown in the model of the nonlinear response of high-temperature superconductors (HTSCs) caused by interband transitions in the electronic spectrum with a metastable energy gap that the Stokes and anti-Stokes components of the HTSC response to picosecond biharmonic pumping are asymmetric, and for the excitation-pulse frequency detuning exceeding 100 cm^-1, the efficiency of self-diffraction in the directions corresponding to these two components is different.

It is shown that the quasi-geometrical approximation permits a quite accurate calculation of the eigenfrequency spectrum of axially symmetric dielectric resonators with whispering-gallery modes and also gives expressions for the radiative Q factor and Q factor related to surface losses.

The structure of the fundamental mode of a laser is calculated by the iteration Fox–Li method in the case of inhomogeneous unsaturated amplification produced by axially symmetric longitudinal pumping. The calculation is performed for different parameters g₁ and g₂ of the resonator within the entire stability region. It is shown that in the case of inhomogeneous amplification, the fundamental mode considerably deviates from the Gaussian mode of an empty resonator only in the so-called critical configurations of the resonator, when the quantity [arccos(g₁g₂)^1/2]/π is zero or takes a number of values expressed by irreducible fractions m/n. For the Fresnel number N_F = 9, configurations with m/n = 1/2, 2/5, 3/8, 1/3, 3/10, 1/4, 1/5, 1/6, 1/8, and 1/10 are pronounced. As N_F increases, the number of critical configurations increases. The expansion in a system of Laguerre–Gaussian beams shows that the fundamental mode in critical configurations is formed by a set of beams with certain radial indices p phased in the active medium.

The Hermite–Gaussian modes up to the third order inclusive are generated in a flashlamp-pumped neodymium phosphate laser and converted to the corresponding Laguerre–Gaussian modes in an astigmatic converter. It is also shown that, by using a laser with the gain minimum on the axis of a plane-spherical resonator and changing its Fresnel number, it is possible to excite efficiently Laguerre–Gaussian modes with the field amplitude dependence .

The dynamics of a wave packet formed by two modes propagating in optically coupled channels with different mode gain increments is studied. It is shown that in the case of a linear intermode coupling, radiation in such structures is decomposed into two autonomous partial pulses with different values of the effective dispersion parameters determining their dynamics. The conditions of the temporal compression and realisation of the superluminal velocity of the envelope maximum for partial pulses and the wave packet as a whole are also investigated.

A brief review of modern applications of scanning near-field optical (SNO) devices in microscopy, spectroscopy, and lithography is presented in the introduction. The problem of the development of SNO probes, as the most important elements of SNO devices determining their resolution and efficiency, is discussed. Based on the works of the authors, two different methods for fabricating SNO probes by using the adiabatic tapering of an optical fibre are considered: the laser-heated mechanical drawing and chemical etching. A nondestructive optical method for controlling the nanometre aperture of SNO probes is proposed, substantiated, and tested experimentally. The method is based on the reconstruction of a near-field source with the help of a theoretical algorithm of the inverse problem from the experimental far-filed intensity distribution. Some prospects for a further refinement of the construction and technology of SNO probes are discussed.