Abstract: Quasi-collinear acousto-optic interaction is studied in acoustically and optically anisotropic paratellurite crystals. The possible applications of this interaction in acousto-optic tunable filters with a high spectral resolution are discussed. Different modifications of devices are compared and variants of devices intended for processing light beams and selection of light signals in fibreoptic communication systems with wavelength division multiplexing (WDM) at λ 1550 nm are considered.

Abstract: Surface nanotexturing of tantalum by ablation with short laser pulses in water has been studied experimentally using three ablation sources: a neodymium laser with a pulse duration of 350 ps, an excimer laser (248 nm) with a pulse duration of 5 ps and a Ti:sapphire laser with a pulse duration of 180 fs. The morphology of the nanotextured surfaces has been examined using a nanoprofilometer and field emission scanning electron microscope. The results demonstrate that the average size of the hillocks produced on the target surface depends on the laser energy density and is ~200 nm at an energy density approaching the laser-melting threshold of tantalum and a pulse duration of 350 ps. Their surface density reaches 106 cm-2. At a pulse duration of 5 ps, the average hillock size is 60–70 nm. Nanotexturing is accompanied by changes in the absorption spectrum of the tantalum surface in the UV and visible spectral regions. The possible mechanisms of surface nanotexturing and potential applications of this effect are discussed.

Abstract: An original method is proposed to calculate the formation of specified far-field intensity distributions by a bimorph mirror in the case of initial transverse-multimode beams. The method is based on the Gerchberg—Saxton algorithm with replacement of the phase function in the plane of the control element by a function that takes into account both the intensity and phase distributions of each mode. The numerical results on the formation of a beam with the third-order super-Gaussian intensity distribution from beams composed of two or four lowest transverse modes are discussed. The experimental results on using the conventional Gerchberg—Saxton algorithm to form a desired intensity distribution from single-mode laser beams using a liquid-crystal modulator are presented.

Abstract: Lasing in bismuth-doped optical fibres in the range 1470–1550 nm has been demonstrated for the first time. The gain media were Bi-doped phosphogermanosilicate and, for the first time, germanosilicate glass fibres. The gain spectrum of the phosphogermanosilicate fibres extends from 1300 to 1550 nm, the range which can be used in next-generation optical fibre communication systems.

Abstract: A review of investigations of kinetic processes in active media oxygen — iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O2 and I2 molecules are considered, and dissociation mechanisms of I2 in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended.

Abstract: We report on the experimental optimisation of the oxygen-assisted CO2 laser cutting of low-carbon sheet steel 5 to 25 mm in thickness. It is shown that the cut edge roughness is minimal when the energy input per unit volume of the material removed and the incident beam power per unit sheet thickness remain constant at ~20 J mm-3 and ~200 W mm-1, respectively, over the entire range of sheet thicknesses examined. The corresponding Peclet number is Pe = 0.5. These results can be used to determine the optimal beam power and cutting speed for a particular sheet thickness. At sufficiently large thicknesses, the conditions that ensure the minimum roughness can be written in the form of relations between nondimensional parameters.

Abstract: The reflection spectra of several concave (spherical and parabolic) periodic Mo/Si, Mg/Si, and Al/Zr multilayer mirrors intended for cosmic experiments were studied with the help of a laser-plasma soft X-ray radiation source. An investigation was made of the reflection spectra of a laboratory aperiodic Mo/Si multilayer mirror optimised for maximum uniform reflectivity in the 125–250-A range. 'Satellites' were observed in the neighbourhood of the principal peak in the spectrum of the periodic 132-A multilayer mirror. High-intensity second-order interference reflection peaks at wavelengths of about 160 A were experimentally revealed in the reflection spectra of the periodic Mo/Si 304-A mirrors. By contrast, the second-order reflection peak is substantially depressed in the spectra of the narrow-band mirrors based on the Mg/Si multilayer structure. The experimental data are compared with theoretical calculations. Manifestations of the NEXAFS structure of the L2,3 absorption edges of Al and Al2O3 were observed in the spectra recorded.

Abstract: The channeling of microwave radiation is demonstrated experimentally in a double line in which a plasma filament produced in air by intense femtosecond laser pulses serves as one of the conductors. It is shown that during the propagation of microwave radiation in this line, ultrashort pulses are formed, their duration monotonically decreasing with increasing the propagation length (down to the value comparable with the microwave field period). These effects can be used for diagnostics of plasma in a filament.

Abstract: The lensing effects in diode end-pumped Yb:YAG laser rods and discs are studied. Two mechanisms of refractive-index changes are taken into account, thermal and electronic (due to the difference between the excited- and ground-state Yb polarisabilities), as well as pump-induced deformation of the laser crystal. Under pulsed pumping, the electronic lensing effect prevails over the thermal one in both rods and discs. In rods pumped by a highly focused cw beam, the dioptric power of the electronic lens exceeds that of the thermal lens, whereas in discs steady-state lensing is predominantly due to the thermal mechanism. © 2009 Kvantovaya Elektronika and Turpion Ltd.

Abstract: The propagation of ultrashort 10-μm laser pulses of power exceeding the critical self-focusing power in xenon and air is numerically simulated. It is shown that the pulse duration in certain regimes in xenon can be decreased by 3–4 times simultaneously with the increase in the pulse power by 2–3 times. It is found that the average energy of electrons in a filament upon filamentation of 10-μm laser pulses in air can exceed 200 eV. The features of the third harmonic and terahertz radiation generation upon filamentation are discussed.

Abstract: The dynamics of the plume ejected from the surface of solid targets (YSZ, Nd:YAG and graphite) by a CO2 laser pulse with a duration of ~500 μs (at the 0.03 level), energy of 1.0–1.3 J and peak power of 6–7 kW have been studied using high-speed photography of the plume luminescence and shadow. The targets were used to produce nanopowders by laser evaporation. About 200 μs after termination of the pulse, shadowgraph images of the plumes above the YSZ and Nd:YAG targets showed dark straight tracks produced by large particles. The formation of large (~10 μm) particles is tentatively attributed to cracking of the solidified melt at the bottom of the ablation crater. This is supported by the fact that no large particles are ejected from graphite, which sublimes without melting. Further support to this hypothesis is provided by numerical 3D modelling of melt cooling in craters produced by laser pulses of different shapes.

Abstract: We studied the transmission spectrum of a one-dimensional photonic crystal containing a defect layer in which electromagnetically induced transparency is possible. The analysis is performed taking into account the spatial inhomogeneity of interacting fields in the photonic crystal. It is found that the transmission spectrum of such a photonic crystal depends on the spatial overlap of defect modes excited by probe and control radiations. It is shown that electromagnetically induced transparency can result in a considerable narrowing of the defect mode spectrum.

Abstract: We have studied the effect of nanosecond laser pulses (λ = 1064 nm) on the optical properties of onion-like carbon (OLC) prepared by high-temperature vacuum annealing of detonation nanodiamond and dispersed in N,N-dimethylformamide (DMF). The results demonstrate that, under low-intensity irradiation, the OLC suspension displays optical limiting behaviour. Increasing the incident intensity leads to bleaching of the suspension in the visible and near-IR spectral regions.

Abstract: Laser-induced fluorescence is used for measuring the concentration of iodine molecules at the output of an electric-discharge generator of atomic iodine. Methyl iodide CH3I is used as the donor of atomic iodine. The fraction of iodine extracted from CH3I in the generator is ~50%. The optimal operation regimes are found in which 80%—90% of iodine contained in the output flow of the generator was in the atomic state. This fraction decreased during the iodine transport due to recombination and was 20%—30% at the place where iodine was injected into the oxygen flow. The fraction of the discharge power spent for dissociation was ~3%.

Abstract: Emission parameters at 1908 nm in a longitudinally-diode-pumped Tm:YLF laser are studied. The laser parameters are optimised to obtain the maximal power of high-quality cw radiation. The output power of ~27 W is obtained at the slope efficiency of ~50% and total optical pump conversion efficiency of ~41%.

Abstract: A method describing radially and azimuthally polarised laser modes is presented, which is devoid of intrinsic contradictions and unjustified restrictions. The solutions of the wave equation found in the paper satisfy Maxwell's equation E = 0. This allowed the calculation of all the components of the fields of such modes, including the longitudinal one. Expressions for tight focusing of radially and azimuthally polarised modes are obtained in the Debye approximation. The methods of intracavity generation of such modes in a high-power industrial CO2 laser are experimentally realised and methods of mutual transformation of these modes outside the cavity are developed. The intracavity generation of azimuthally polarised modes was achieved by using as a rear highly reflecting mirror either V-shaped axicons or metal diffraction mirrors with the relief period comparable to the wavelength. Radially polarised radiation was generated by using diffraction mirrors with the relief period of the order of two wavelengths. The polarisation-nonuniform TEM01* and TEM11* modes of power up to 1.8 kW are generated for the first time. In this case, the degree of polarisation was close to 100% within the entire radiation power range both in the near- and far-field zones. By using two half-wave phase shifters, the azimuthally polarised radiation is transformed to radially polarised radiation and vice versa, the energy efficiency of this transformation being 92%. These results open up the possibility for industrial applications of such radiation.

Abstract: An experiment has been proposed, theoretically substantiated and accomplished which has provided conclusive evidence in favour of one of two models for the behaviour of polarised light in optical fibres fabricated by spinning preforms with a high built-in linear birefringence (spun fibres): a helical structure of the built-in linear birefringence axes and circular birefringence. The experiment, carried out with a reflective fibreoptic dual-polarisation interferometer, has shown that the behaviour of polarisation states in spun fibres can be understood in terms of a helical structure of the built-in linear birefringence axes.

Abstract: We have studied the effect of process parameters on the mode profile in lithium niobate channel waveguides produced by low-temperature proton exchange. A model has been proposed for the processes underlying waveguide formation, and has been used to numerically calculate the mode profile for various fabrication parameters. We have identified low-temperature proton exchange conditions which ensure high electro-optical performance of the waveguides and stability towards fabrication errors. The obtained results may be helpful in optimising integrated optical devices and matching them to various types of optical fibres.

Abstract: We report an experimental study of the first cw solid-state Raman laser operating simultaneously at the frequencies of the first and second Stokes components. Simultaneous generation is ensured by a cavity with an enhanced finesse at both Stokes frequencies. The threshold pump powers for the first (3.4 W) and second (3.67 W) Stokes components suggest that the second Stokes generation follows a cascade mechanism. We demonstrate for the first time Raman conversion with intensity stability exceeding the pump radiation stability and show that this approach may find application in Raman spectroscopy.

Abstract: Crystals of high-power laser diodes are directly mounted on copper heat-removing elements. The maximum output power of 25 W is obtained many times in a 808-nm cw laser with the 150-μm-wide strip contact at 20°C. After training tests at the output power of 6 W for 200 hours, the yield of acceptable samples was 80 %. No changes in the output parameters were observed after tests for 70 hours at the output power of 8.5 W. Tests are being continued.

Abstract: A simple analytical method for calculating open stable laser cavities suggested earlier by the author is used for calculating losses and for performing efficient optimisation of an open optical resonator of the Novosibirsk terahertz free- electron laser. The gain and cavity losses are measured at various wavelengths. Good agreement between theory and experiment is observed. Optimisation of useful losses is considered and a correct expression is derived for their calculations in lasers with uniform saturation of the active medium. Possible potential modernisation of the laser resonator is considered, which may provide greater than twice the output power.

Abstract: It is found that upon irradiation of a mixture of the atmospheric air and carbon particles of size 30-300 {mu}m at a concentration of {approx}10{sup 2} cm{sup -3} by a cw CO{sub 2} laser, the active combustion of particles in the mixture appears when the radiation intensity in the focal region achieves {approx}10{sup 3} W cm{sup -2}. The dependences of the threshold radiation intensity for the evaporation of particles on their radius are obtained for a gaseous dust medium in the form of a free vertical jet of spherical aluminium and carbon microparticles in nitrogen. It is shown that particles of size {approx}10 {mu}m can be completely evaporated in a focused cw laser beam of power {approx}10{sup 2} W. (interaction of laser radiation with matter. laser plasma)

Abstract: The method based on the generalisation of the phase screen method for a continuous random medium is proposed for simulating numerically the propagation of laser radiation in a turbulent atmosphere with precipitation. In the phase screen model for a discrete component of a heterogeneous 'air—rain droplet' medium, the amplitude screen describing the scattering of an optical field by discrete particles of the medium is replaced by an equivalent phase screen with a spectrum of the correlation function of the effective dielectric constant fluctuations that is similar to the spectrum of a discrete scattering component — water droplets in air. The 'turbulent' phase screen is constructed on the basis of the Kolmogorov model, while the 'rain' screen model utilises theexponential distribution of the number of rain drops with respect to their radii as a function of the rain intensity. Theresults of the numerical simulation are compared with the known theoretical estimates for a large-scale discrete scattering medium.

Abstract: The ratio of 12NO2 and 13CO2 concentrations in the human exhaled air is measured by the method of diode laser spectroscopy using a three-channel optical scheme and multipass cell. Unlike the previous measurements in the spectral range of ~4.3 μm with a resolved rotational structure at low pressure of selected samples, the present measurements are performed in the range of ~2 μm, in which weaker absorption bands of CO2 reside. In this case, it is possible to employ lasers and photodetectors operating at room temperature. The thorough simulation of the spectrum with collisional broadening of lines and employment of regression analysis allow one to take measurements at atmospheric pressure with the accuracy of ~0.04%, which satisfies the requirements to medical diagnostics of ulcers.

Abstract: We report a procedure for temperature and water vapour concentration measurements in an unsteady-state combustion zone using diode laser absorption spectroscopy. The procedure involves measurements of the absorption spectrum of water molecules around 1.39 μm. It has been used to determine hydrogen combustion parameters in M = 2 gas flows in the test section of a supersonic wind tunnel. The relatively high intensities of the absorption lines used have enabled direct absorption measurements. We describe a differential technique for measurements of transient absorption spectra, the procedure we used for primary data processing and approaches for determining the gas temperature and H2O concentration in the probed zone. The measured absorption spectra are fitted with spectra simulated using parameters from spectroscopic databases. The combustion-time-averaged (~50 ms) gas temperature and water vapour partial pressure in the hot wake region are determined to be 1050 K and 21 Torr, respectively. The large signal-to-noise ratio in our measurements allowed us to assess the temporal behaviour of these parameters. The accuracy in our temperature measurements in the probed zone is ~40 K.

Abstract: We report a simple design of spun holey fibres and the first experimental study of the magneto-optical response of spun microstructured fibres with high built-in birefringence. Such fibres enable the Faraday-effect-induced phase shift to effectively accumulate in a magnetic field even at very small coiling diameters. For example, the magneto-optical sensitivity of a 5-mm-diameter fibre coil consisting of 100 turns is ~70% that of an ideal fibre, in good agreement with theoretical predictions.

Abstract: Lasing at 337.1 and 357.7 nm is obtained upon excitation of nitrogen molecules by a toroidal pulsed inductive discharge. A system for formation of a pulsed inductive discharge for exciting gas lasers is described. The spontaneous emission spectra of the nitrogen inductive discharge plasma and the emission spectrum of the nitrogen laser are recorded and interpreted. The dependences of the energy and duration of laser pulses on the resonator Q factor and pump level are studied. The output energy of the inductive nitrogen laser emitting 15±1-ns pulses achieves 4.5 mJ. The generation of high-power 300-kW pulses is obtained for the first time at a low (~1 Torr) pressure of pure nitrogen. The spatial distribution of the laser radiation intensity in the discharge tube cross section is investigated. The cross section of the radiation beam of the inductive nitrogen laser had the shape of a ring with the external diameter of 34 mm and width ~4 mm, its divergence being ~0.8 mrad. The average output power of the laser achieved 120 mW at a pulse repetition rate of 30 Hz.

Abstract: Pulse synchronisation with an accuracy of no worse than ±5 ns is demonstrated in passively Q-switched neodymium phosphate glass and Nd:YAG lasers. Two operating regimes are realised: the 'sub-threshold' regime (when the slave Nd:YAG laser does not generate a giant pulse if its passive Q switch is not irradiated by the master Nd:glass laser) and the 'above-threshold' regime (when the pulse irradiating the passive Q switch of the slave laser advances its generation).

Abstract: The time dynamics of plasma-emission spectra is studied experimentally at different stages of the drilling of a steel plate by 100-fs and 5-ps laser pulses: from a shallow crater to a hole. The change in the time dependence of the plasma temperature caused by variations in the irradiated surface geometry is analysed. It is found that the time interval needed to reach a particular temperature (about 8000 K) drastically increases from 40–50 to 150–200 ns when a specific crater depth is achieved. The opposite tendency is observed as the crater depth grows further and a hole is produced. Strong self-absorption in a plasma plume inside a deep crater is experimentally confirmed which results in the appearance of line absorption against a continuous emission spectrum.