Table of contents

The influence of the amplified luminescence (AL) and spreading of nonequilibrium charge carriers on the threshold, dynamic, and power characteristics of high-power InGaAs/AlGaAs laser diode arrays (LDAs) is studied. It is found that, depending on the near-field fill factor, the contribution of AL-induced recombination to the lasing threshold of LDAs may reach 11%. It is shown that the losses of the LDA pump energy, associated with the AL, increase with the injection current growth above its threshold value because of the increase in the intensity of radiation, propagating normally to the LDA cavity axis.

Relations for estimating the reliability of heterolasers operating under irradiation conditions are calculated based on the probabilistic analysis. The accumulation of defects in their active regions is considered to be the physical cause of their failure.

We report an experimental study of the polarisation dynamics of a dual-polarisation microchip Nd:YAG ceramic laser. Our results demonstrate dual-polarisation operation of the polycrystalline Nd:YAG laser. The low-frequency dynamics in this regime involves three types of relaxation oscillations, two of which are responsible for antiphase dynamics of the intensities of orthogonally polarised modes. Linearly polarised pump light induces gain anisotropy in the Nd:YAG ceramic, as in Nd:YAG single-crystal lasers. We present a comparative analysis of the behaviour of orthogonally polarised modes in Nd:YAG single-crystal lasers and the Nd:YAG ceramic laser, with a random orientation of the crystallographic axes in each grain (microcrystal), describe a technique for evaluating the total cavity loss from the relaxation oscillation spectrum and compare single-crystal and ceramic active elements. Experimental evidence is presented for gain anisotropy, loss anisotropy and phase anisotropy in ceramic and single-crystal microchip lasers.

The problem of the maximum pulse duration τ_max of self-terminating lasers is considered. It is shown that the duration depends on the transition probability in the laser channel, on the decay rate of the resonant state in all other channels, and on the excitation rate of the metastable state. As a result, τ_max is found to be significantly shorter than previously estimated. The criteria for converting the 'self-terminating' lasing to quasi-cw lasing are determined. It is shown that in the case of nonselective depopulation of the metastable state, for example in capillary lasers or in a fast flow of the active medium gas, it is impossible to obtain continuous lasing. Some concrete examples are considered. It is established that in several studies of barium vapour lasers (λ = 1.5 μm) and nitrogen lasers (λ = 337 nm), collisional lasing is obtained by increasing the relaxation rate of the metastable state in collisions with working particles (barium atoms and nitrogen molecules).

A planar repetitively pulsed microwave-pumped CO₂ laser with discharge channel lengths of 250 and 470 mm is experimentally investigated. An average laser power of 60 W at a wavelength of 10.6 μm is attained. A peak power of 1300 W is reached in the repetitively pulsed regime. The dependences of the shape and energy of CO₂ laser pulse on the introduced power, working gas mixture composition and pressure, and pump-pulse repetition rate and width are analysed.

The absorption spectra of nonlinear laser crystals Y_1-xYb_xAl₃(BO₃)₄ grown from bismuth—lithium—molybdate and potassium—molybdate solution—melts are comparatively studied by high-resolution Fourier spectroscopy. The differences observed in the fine structure of the absorption spectra are correlated with the variations in the solution—melt composition and in the concentrations of bismuth and molybdenum impurities in the crystals. It is shown that the concentration of the molybdenum impurity (the main factor hindering lasing in the UV spectral region) in the single crystals grown from the bismuth—lithium—molybdate solutions is more than an order of magnitude smaller than in the crystals grown using the potassium—molybdate solution—melt. The described method can be used for express analysis of the quality of UV laser crystals and for improving the solution—melt technologies of growth of laser crystals and crystals used for generation of the fourth harmonic of Nd:YAG laser radiation.

Lead pyrovanadate Pb₂V₂O₇ single crystals of optical quality suitable for laser experiments are obtained. Vibrational modes are identified based on the analysis of the polarised Raman spectra of the single crystals. The main parameters (width at half maximum, peak and integral intensities) of the spectral lines most promising for SRS conversion in this material are estimated. These parameters are compared with the corresponding parameters of the most frequently used lines of known Raman materials: yttrium and gadolinium vanadates, potassium and lead tungstates, and lead molybdate.

We set forth an improved technique for the investigation of collisional quenching in high-pressure rare-gas mixtures, which relies on the absorption probing measurements of the decay rates of the excited states of these gases in the afterglow of a fast electron beam discharge. We determined more precisely the rate coefficients of the plasmochemical reactions Xe* + Xe + Ar → Xe₂* and Xe*+Ar → products + Ar for the metastable (6s[3/2]₂⁰) and resonance (6s[3/2]₁⁰) levels of atomic Xe investigated in our earlier work. The rate coefficients for the reactions Xe(6s[3/2]₂⁰) + 2Ar → ArXe* + Ar((7.2±1.4)×10^-36 cm⁶ s^-1) and Xe(6s[3/2]₁⁰) + 2Ar → ArXe*((5.3±2.4)×10^-36 cm⁶ s^-1) were measured for the first time.

The dependence of the ratio of specific powers of dimole radiation of singlet oxygen in the 634 nm band and in the b — X band of the O₂(¹Σ) molecule in the O₂(X) — O₂(¹Δ) — O₂(¹Σ) — H₂O — CO₂ mixture on the CO₂ concentration is measured. As a result, the rate constant of the reaction O₂(¹Δ) + O₂(¹Δ) → O₂(¹Σ) + O₂(³Σ) at the temperature ∼330 K is found to equal (4.5 ± 1.1) 10^-17 cm³ s^-1.

An attempt is made to produce gas-phase singlet oxygen O₂(a¹Δ_g) in a liquid-liquid reaction between acidic hydrogen peroxide (AHP) and sodium hypochlorite (NaOCl). The attempt arises from the fact that basic hydrogen peroxide (BHP) has long been the prime source for producing singlet delta oxygen through its reaction with chlorine. However, BHP suffers from the defect of being unstable during storage. Exploratory experiments were performed in a centrifugal flow singlet oxygen generator (CF-SOG) with two streams of solutions, AHP and NaOCl, mixed in a slit nozzle and then injected into the arc-shaped concavity in the CF-SOG to form a rotating liquid flow with a remarkable centrifugal force. With the help of this centrifugal force, the product of the O₂(¹Δ) reaction was quickly separated from the liquid phase. The gas-phase O₂(¹Δ) was detected via the spectrum of O₂(¹Δ) cooperative dimolecular emission with a CCD spectrograph. Experimental results show that it is feasible to produce gas-phase O₂(¹Δ) from the AHP + NaOCl reaction, and the stronger the acidity, the more efficient the O₂(¹Δ) production. However, since in the AHP + NaOCl reaction, Cl₂ unavoidably appears as a byproduct, its catalytic action on the decomposition of H₂O₂ into ground-state O₂ remains a major obstacle to utilising the AHP + NaOCl reaction in producing gas-phase O₂(¹Δ). Qualitative interpretation shows that the AHP + NaOCl reaction is virtually the reaction of interaction of molecular H₂O₂ with molecular HOCl, its mechanism being analogous to that of reaction of BHP with Cl₂, where HOOCl is the key intermediate. It is difficult to form the intermediate HOOCl via the H₂O₂ + NaOCl reaction in a basic medium, thus gas-phase O₂(¹Δ) cannot be obtained in appreciable quantities.

We consider for the first time three-wave interactions of bulk quasi-static defect-deformation (DD) waves (generation of the second DD harmonic and summation of the wave vectors), similar to three-wave interactions in nonlinear optics and acoustics, leading to cascaded broadening of the spectrum of spatial DD harmonics. Based on the theory developed, we interpret the recently observed effect of laser-induced generation of the bulk periodic structure of silver nanoparticles with a discrete spatial spectrum, extending from micro- to nanometres.

Polarisation singularities in the electric field at a sum-frequency generated in the bulk of an isotropic gyrotropic medium with a quadratic nonlinearity are predicted to appear in the case of the collinear interaction of two uniformly elliptically polarised Gaussian beams. The parameters of the fundamental waves are found, corresponding to the formation of lines with circular and linear polarisations (C- and L-lines) in the cross section of the beam at the sum-frequency as well as to the appearance of the regions in the signal beam where the polarisation state varies smoothly from the left-hand circularly polarised state to the right-hand circularly polarised. In this case, the ellipticity degree of the polarisation ellipse takes all possible values, while its orientation remains unchanged.

Efficient compression of focused ∼0.9-ns pulses of a miniature Nd:YAG laser to less than 60 ps is experimentally obtained at their interaction with counterpropagating pulses of the same carrier frequency and width in CCl₄. In this case, electrostriction interaction (amplification) begins not from the level of spontaneous-scattering noise; therefore, the counterpropagating pulses can be compressed at pump pulse energies below the stimulated Brillouin scattering (SBS) threshold energies. When counterpropagating seed pulses are used, the energy and temporal stability of compressed pulses are several times higher, and their time jitter is smaller than that for SBS compression from the level of spontaneous-scattering noise.

A numerical investigation was made of the formation and development of filaments in the propagation of high-power femtosecond Gaussian laser pulses in argon, whose polarisation is close to the linear or circular one. Filaments produced by close-to-circularly polarised pulses were found to be more uniform, greater in diameter, and higher in intensity than the filaments produced by close-to-linearly polarised pulses. For incident pulses with a close-to-linear (circular) polarisation, the degree of ellipticity of the radiation on the axis of the resultant filament becomes equal to zero (unity) at the instant of the peak of the local intensity.

Optical properties of a semi-infinite dielectric medium comprising a monolayer quasi-crystal of nanoparticles are considered. It is shown that imbedding a single layer of nano-objects regularly distributed in space under certain conditions may provide close to 100 % transmission of the medium in a wide spectral range.

We study the possibility of differentiation of optical anisotropy properties of biological tissues in different physiological conditions by means of statistical analysis of coordinate distributions of a new analytic parameter, namely, the complex degree of mutual anisotropy of extracellular matrix, formed by a network of birefringent filament-like protein crystals.

We have designed and implemented a new fibre-optic phase-sensitive coherent reflectometer configuration, which allows one to avoid signal fading owing to the use of a two-fibre scattered-light interferometer.

A method is proposed to reconstruct three-dimensional images of a distant nonplanar rough object by the speckle pattern of its flat image, which is calculated using the temporal approach based on the time correlation function of probe radiation with a coherence length smaller than the size of the probed object. We analyse the influence of the angular resolution of the optical system, forming an image of the object, and additive noises on the reconstruction accuracy of the object surface shape using the proposed method.

The influence of axially symmetric perturbations of the intensity and phase of the laser beam on its focusing by means of an axicon is considered. It is shown that such perturbations give rise to variations in the radiation energy density on the axicon axis with two periods, Λ/γ and Λ²/λ, where λ is the period of perturbation of the laser beam intensity, and γ is the angle of convergence of the focused beam.