Table of contents

The amplification of weak 80–240-mJ, 4-ns laser pulses with a gain of 0.035–0.045 cm^-1 is studied. The maximum energy of 3.3 kJ is obtained for 4-ns pulses.

A five-stage neodymium phosphate glass amplifier producing 1–1.5-ns radiation pulses of energy up to 110 J is described. The use of a multistage spatial filter based on an aperture line provides efficient extraction of the stored energy. The exit aperture filling factor is 0.65 and the output radiation divergence is equal to three times the diffraction-limited divergence. The energy efficiency of radiation conversion to the second harmonic is 60%. The amplifier is intended for pumping a chirped-pulse optical parametric amplifier.

A XeF electric-discharge laser with a pulse repetition rate f of up to 4 kHz is developed. The laser electrode unit is based on plate electrodes with inductive—capacitive discharge stabilisation. He and Ne are used as buffer gases, and NF₃ serves as a fluorine donor. A narrow (∼1 mm) discharge is achieved; the specific energy deposition per unit length of the active volume is as high as 2 J m^-1. The maximum energy in a laser pulse is ∼3 mJ for NF₃—Xe—He and NF₃—Xe—Ne mixtures at total pressures of 0.8 and 1.2 atm, respectively, and the maximum lasing efficiency is ∼0.73%. The maximum gas velocity in the working gap is 19 m s^-1. The laser-pulse energy at a high pulse repetition rate (4 kHz) virtually coincides with that obtained at a low repetition rate. The mean output pulse power at f = 4 kHz reaches 12 W, and the rms deviation of the laser-pulse energy is ∼2.5%.

The spectral profile of the optical gain and the spectral dependence of the coefficient characterising the variation in the refractive index with a carrier concentration are calculated using the three-band model for an active quantum-well InGaAs layer. A comparison of the theoretical results with the experimental data gave values of parameters allowing the numerical simulation of the material parameters of the active layer with a high degree of accuracy.

A model of a fibre laser is proposed which gives an analytic expression relating the laser wavelength to the main parameters of the laser. It is shown that there exists a region of the ambiguous dependence of the laser wavelength on the temperature and length of the active medium. Experimental results agree quantitatively with the theoretical model in a broad spectral range of laser radiation. Two-wave lasing without an intracavity selecting element is predicted and observed for the first time.

Single-mode cw Yb-, Er—Yb, and Nd-doped fibre lasers are fabricated by using fibres of a complicated structure (a few silica fibres in optical contact with each other are surrounded by a polymer jacket). Such a structure allows the coupling of radiation from several pump sources into one active fibre, providing an increase in the output power of the fibre laser. The Yb-doped fibre lasers with the output power above 50 W and efficiency ∼65% and the 1.608-μm Er—Yb-doped fibre laser pumped to the absorption band of Yb are fabricated and studied. The Nd-doped fibre lasers based on such fibres and emitting at 0.92 and 1.06 μm are manufactured for the first time.

A two-stage Raman fibre converter (1.089/1.273/1.533 μm) based on a P₂O₅-doped silica fibre is fabricated and studied. The spectral broadening of the first Stokes component is investigated. The Raman converter is simulated numerically. By using the experimental data, the method of Raman converter simulation is improved by taking into account the additional power loss of the first Stokes component. The results of calculations by the improved method are in good agreement with the experiment. It is shown that the additional power loss of the first Stokes component results in a change in the region of the optimal resonator length from 300–600 m to 600–800 m.

An efficient cladding-pumped Yb-doped fibre laser with a Bragg grating written in a multimode graded-index fibre is fabricated for the first time. The laser emits one transverse mode with a slope efficiency of 60%. The resonator design proposed in the paper can be used for the development of high-power fibre lasers with an increased fibre core diameter.

A new scheme with an intra-cavity loss element for small-signal gain measurement at two main wavelengths of a tunable gas flow longitudinally excited CO₂ laser is presented. By inserting a ZnSe stack polariser into the cavity, the critical condition for the laser is obtained. The small-signal gain and saturation intensity are calculated using the Rigrod formula. The small-signal gain measurement was performed for different gas pressures and different input electric powers. Under the same experimental conditions, the values of the saturation intensities were calculated from the output power and the measured small-signal gains. The advantage of this method is that no probe laser system is required. The results agree with experimental data obtained earlier by the conventional oscillator—amplifier method.

A method for amplification of picosecond pulses in F₂^-:LiF crystals synchronously pumped by picosecond and nanosecond pulses is proposed and demonstrated. Due to two-stage amplification of a train of 22-ps, 1150-nm SRS pulses generated by a PbMoO₄ crystal, a power gain of (2-4)× 10³ is achieved and single 6-ps, 0.88-mJ pulses are obtained.

The results of experimental investigation of a low-temperature plasma produced by laser irradiation at the surface of metal targets are reported. The optical characteristics and the plasma pressure in the laser plume are found to exhibit a threshold behaviour under vaporised-material density variation. The results are interpreted using the model of a coupled plasma state with limitation of plasma expansion.

The coherent interaction of Gaussian light beams polarised parallel to the [10] direction in a cubic optically active photorefractive crystal with the ( 0) cut is studied in an electric field applied to the crystal in the [00] direction. The effect of optical activity on the interaction of the light beams with the phase difference Δ=0, π/2, and π is theoretically studied. It is shown that, while a change in the intensity of a combined light beam at Δ=0 caused by the influence of optical activity in a 9-mm thick Bi₁₂TiO₂₀ crystal is comparatively small (less than 8%), this change achieves 36% in the crystal of thickness 18 mm. The interaction of orthogonally polarised beams in this crystal is considered. It is found that, although the optical activity of the crystal results in the appearance of the 'breathing effect', a soliton-like nature of the combined beam is preserved. The results obtained can be used for the address positioning of soliton-like light beams.

A simple orthogonality relation for the modes of an open cavity is obtained in the scalar field approximation. The relation directly follows from the wave equation and boundary condition at the cavity mirrors and can be applied for a broad class of systems with a cavity that can contain a random gain medium with a weak dispersion.

The near-field energy-density distribution of a beam from an HF electric-discharge laser with an inductively stabilised discharge, an SF₆- and H₂-based active medium, and interelectrode gaps of 34 and 52 mm is studied. Plates 1-mm thick and 60- or 120-mm wide oriented at an angle of 30° to the optical axis serve as 60-mm-wide electrodes. Electrodes 30-mm wide are formed by 60-mm-wide plates also oriented at an angle of 30° to the optical axis. The distributions of the laser-radiation density in a resonator with flat mirrors and the discharge-emission intensity over the resonator cross section are studied. The distributions of the laser-radiation density in the near-field zone and the discharge-emission intensity have similar profiles. The arrangement of the electrode plates at an angle of 30° provided a considerable increase in the width of the lasing region. The FWHM of the laser-radiation distribution is ∼80% of the electrode width for the both interelectrode gaps.

Correlation properties of light beams upon self-phase modulation in a thin layer of a medium with thermal nonlinearity are studied. It is found out that the efficiency of spatial coherence transformation of radiation is determined by the ratio of the characteristic coherence radius of the initial radiation to the size of phase inhomogeneities induced in the nonlinear medium.

The role of coherent optical radiation in photoregulatory processes caused by chemiluminescence of living cells is discussed. The effect of low and highly coherent quasi-monochromatic light on a dynamic 'host—parasite' system is studied. It is shown that plant organisms can distinguish the statistical order of irradiation. A significant increase in the functional activity was observed only for cells that were completely located within the coherence volume of the electromagnetic field. It is concluded that the cell size in living organisms is the discrimination threshold of the statistical properties of radiation and may serve as a specific biological measure of coherence.

A method is proposed and a device is described for determining the electrodynamic parameters of one-dimensional wire gratings in the submillimetre range. The grating under study was used as the output mirror of the laser. The transmission coefficient and the phase shift are determined experimentally for several gratings with different parameters at a wavelength of 337 μm.

The method of intracavity laser spectroscopy using a Co:MgF₂ laser is applied to record the absorption spectra from the first excited a¹Δ_g state of gaseous molecular oxygen at the a¹Δ_g → b¹Σ_g⁺ transition at 1.91 μm. The gas flow from a chemical singlet oxygen generator with a known concentration of singlet oxygen O₂ (a¹Δ_g) was supplied to the cavity of the Co:MgF₂ laser. The absorption line intensities are measured for five spectral lines of the Q-branch of the 0–0 vibrational band for the a¹Δ_g → b¹Σ_g⁺ transition. The O₂ (b¹Σ_g⁺ → a¹Δ_g) transition probability calculated from these data was (1.20 ± 0.25) × 10^-3 s^-1.

The laser-plasma method is developed for diamond synthesis in air without using vacuum or reaction chambers. The design of a laser plasmotron based on a 3-kW cw CO₂ laser for synthesis of diamond films on substrates of size 3–4 times larger than the transverse size of the plasma jet is presented. Various regimes of plasmotron operation while moving the substrate relative to the laser plasma are considered. Possible directions in further investigations in the field of laser plasma synthesis of diamond on large areas are discussed.

It is shown that due to the quantum coherence of atoms in a Bose—Einstein condensate, the width of gamma lines of the long-lived metastable states of isomeric nuclei in these atoms can be close to the natural radiative width. This opens up the possibility of observing super-narrow gamma lines, which are narrower by a few orders of magnitude than the Mössbauer gamma line.