Table of contents

We report the first cw bismuth — germanium codoped silica fibre laser with an output power above 20 W at 1460 nm and 50% optical efficiency. The laser operates on a transition between energy levels of bismuth-related active centres associated with silicon. The incorporation of a small amount (∼5 mol %) of germanium into the core of bismuth-doped silica fibre has little effect on its luminescence spectrum but reduces optical losses, which limit the laser efficiency.

Luminescent and lasing properties at the ⁴F_3/2 — ⁴I_11/2 transition of α-cut Nd:YVO₄, Nd:GdVO₄, Nd:Gd_1-xY_xVO₄ and Nd:Sc_1-xY_xVO₄ vanadate crystals are experimentally studied for π- and σ-polarisations. Polarisation dependences of the lasing characteristics of passively Q-switched Nd:YVO₄, Nd:Gd_1-xY_xVO₄ and Nd:Sc_1-xY_xVO₄ lasers with Cr⁴⁺:YAG and V³⁺:YAG Q-switches are investigated. It is shown that the laser wavelengths are different for π- and σ-polarizations. The best characteristics are achieved for the Nd:YVO₄ laser with a Cr⁴⁺:YAG passive saturable absorber for σ-polarisation (minimum pulse duration shorter than 3 ns, maximum peak power up to 10 kW, maximum peak energy ∼35 μJ at a slope efficiency up to 32%).

We analyse the concept of collinearly pumped active medium consisting of multiple thin disks (multi-disk configuration). The multiple disk design is attractive for fabrication of mid- and high-output power laser systems with a good spatial beam quality and high optical efficiency. Two approaches for realisation such multi-disk active elements are considered. Preliminary lasing experiments and numerical calculations for temperature distribution inside the lasing medium are presented.

A method of service life tests of SLD-37 quantum-well superluminescent diodes (SLDs), which are widely used in optical coherence tomography, is described and the results of tests are presented. Special attention is given to variations in the emission spectra of SLDs during their aging. It is shown that this method can be used as an incoming test to select processed semiconductor heterostructures with the longest expected lifetime for fabrication of active elements of SLD modules.

A multi-wavelength Brillouin fibre laser (MBFL) with an ultra-wideband tuning range from 1420 nm to 1620 nm is demonstrated. The MBFL uses an ultra-wideband semiconductor optical amplifier (SOA) and a dispersion compensating fibre (DCF) as the linear gain medium and nonlinear gain medium, respectively. The proposed MBFL has a wide tuning range covering the short (S-), conventional (C-) and long (L-) bands with a wavelength spacing of 0.08 nm, making it highly suitable for DWDM system applications. The output power of the observed Brillouin Stokes ranges approximately from —5.94 dBm to —0.41 dBm for the S-band, from —4.34 dBm to 0.02 dBm for the C-band and from —2.19 dBm to 0.39 dBm for the L-band. The spacing between each adjacent wavelengths of all the three bands is about 0.08 nm, which is approximately 10.7 GHz for the frequency domain.

A 290-fs radiation pulse of an ytterbium laser system with a central wavelength of 1028 nm and an energy of 145 μJ was compressed to a 27-fs pulse with an energy of 75 μJ. The compression was realised on the basis of the effect of pulse spectrum broadening in a xenon-filled glass capillary for a pulse repetition rate of 3kHz.

Saturable absorbers with balanced slow and fast recovery mechanisms exhibiting a broadband recovery dynamics are shown to be advantageous for both reliable start-up of passive mode-locking and efficient pulse shortening.

This paper presents an experimental study of the effect of laser irradiation of aqueous uranyl chloride solutions containing gold nanoparticles on the activity of the uranium series radionuclides ²³⁴Th, ^234mPa, and ²³⁵U. The solutions were exposed to femtosecond Ti:sapphire laser pulses and to the second or third harmonic of a Nd:YAG laser (150-ps pulses) at a peak intensity in the medium of ∼10¹² W cm^-2. The activities of the radionuclides in the irradiated solutions were shown to differ markedly from their equilibrium values. The sign of the deviation depends on the laser wavelength. The measured activity deviations can be interpreted as evidence that laser exposure of nanoparticles accelerates the alpha and beta decays of the radionuclides. The observed effects are accounted for in terms of a mechanism that involves resonant enhancement of optical waves by metallic nanoparticles.

The effect of the 248-nm KrF and 355-nm YAG:Nd³⁺ laser radiation on the surface morphology and chemical composition of SrTiO₃, Sr₂RuO₄, PbMoO₄, LiNbO₃, Y₃Al₅O₁₂, and Al₂O₃ crystals has been studied. A relationship between the laser energy density on the sample surface and the surface roughness caused by the irradiation is determined. A technique for determining exactly the geometric surface characteristics is proposed. The effect of the surface roughness on the results of energy-dispersive X-ray (EDX) microanalysis has been investigated. A method for correcting the EDX data for samples with a rough surface has been developed. It is shown that the small variation in the composition of PbMoO₄, LiNbO₃, Y₃Al₅O₁₂, and Al₂O₃ samples after laser irradiation can be explained by the measurement error, related to the change in the surface roughness. At the same time, the irradiation of SrTiO₃ and Sr₂RuO₄ crystals by a YAG:Nd laser changes the chemical composition of their surface layers.

Propagation of pulses from an Nd:YAG laser (wavelength, 1.064 μm; pulse duration, 270 ns; pulse energy, 225 μJ) through crystalline silicon wafers is studied experimentally. Mathematical modelling of the process is performed: the heat conduction equation is solved numerically, the temperature dependences of the absorption and refraction of a substance, as well as generation of nonequilibrium carriers by radiation are taken into account. The constructed model satisfactorily explains the experimentally observed intensity oscillations of transmitted radiation.

The thermochemical method for recording data, which is based on local laser oxidation of a thin metal film with subsequent etching of the unirradiated region, is an alternative to laser photolithography and direct laser removal of the film material. This recording technology is characterised by the absence of thermal and hydrodynamic image distortions, as in the case of laser ablation, and the number of necessary technological operations is much smaller as compared with the photomask preparation in classical photolithography. The main field of application of the thermochemical technology is the fabrication of diffraction optical elements (DOEs), which are widely used in printers, bar-code readers, CD and DVD laser players, etc. The purpose of this study is to increase the resolution of thermochemical data recording on thin chromium films.

We have measured the temperature in the core of rare-earth-doped optical fibres under lasing conditions at high optical pump powers using a fibre Mach — Zehnder interferometer and probe light of wavelength far away from the absorption bands of the active ions. From the observed heating kinetics of the active medium, the heat transfer coefficient on the polymer cladding — air interface has been estimated. The temperature of the active medium is shown to depend on the thermal and optical properties of the polymer cladding.

We consider theoretical, experimental and numerical methods which make it possible to analyse the key characteristics of laser radiation scattered in the integrated-optical waveguide with three-dimensional irregularities. The main aspects of the three-dimensional vector electrodynamic problem of waveguide scattering are studied. The waveguide light scattering method is presented and its main advantages over the methods of single scattering of laser radiation are discussed. The experimental setup and results of measurements are described. Theoretical and experimental results confirming the validity of the vector theory of three-dimensional waveguide scattering of laser radiation developed by the author are compared for the first time.

The issues related to high-precision measurement of the absorption line profiles of water vapour and its isotopomers using the methods of diode laser spectroscopy in the near IR range aimed at the analysis and detection of greenhouse gases are considered. The absorption line shape of H₂¹⁶O is investigated as a function of pressure of different buffer gases. The influence of the instrument function of the diode laser (DL) on the precision of measuring the line profile is studied. From fitting the profile of Doppler-broadened H₂¹⁶O absorption line to a model profile the lasing line width of the DL with a fibre pigtail is determined. The frequencies and intensities of absorption lines of water isotopomers H₂¹⁶O, H₂¹⁷O, H₂¹⁸O, and HDO are measured in the range of DL oscillation. Analytical spectral regions are chosen for distant probing of water vapour using an airborne lab.

A simple scanning interferometer is implemented for measuring the emission linewidth of single-frequency semiconductor lasers. The free dispersion region of the interferometer is 28 MHz, the spectral resolution being 470 kHz.

The laser method of ultracold neutron (UCN) production consists in slowing down thermal neutrons through their repeated elastic collisions with nuclei pre-cooled to a temperature of ∼1 μK by known methods of laser manipulation of neutral atoms, i.e., this method actually reproduces the known nuclear industry technology in the subthermal range. The feasibility condition for this UCN production process is its short duration, compared with the neutron lifetime. Estimates for a simplified model of the process indicate the possibility of producing the fluxes of UCNs at a concentration several orders of magnitude higher than that obtained with the present method of UCN extraction from the low-energy wing of the Maxwellian energy distribution. Necessary adjustments of the model used for estimates as well as possible applications of the laser method of UCN production are indicated.

Innovative noninvasive material analysis techniques are applied to determine archaeometallurgical characteristics of copper-alloy coins from Florence's National Museum of Archaeology. Three supposedly authentic Roman coins and three hypothetically fraudolent imitations are thoroughly investigated using laser-induced plasma spectroscopy and time of flight neutron diffraction along with 3D videomicroscopy and electron microscopy. Material analyses are aimed at collecting data allowing for objective discrimination between genuine Roman productions and late fakes. The results show the mentioned techniques provide quantitative compositional and textural data, which are strictly related to the manufacturing processes and aging of copper alloys.

The possibility of clearing hazardous near-Earth space debris using a spaceborne laser station with a large autonomous cw chemical HF laser is substantiated and the requirements to its characteristics (i.e., power and divergence of laser radiation, pulse duration in the repetitively pulsed regime, repetition rate and total time of laser action on space debris, necessary to remove them from the orbits of the protected spacecrafts) are determined. The possibility of launching the proposed spaceborne laser station to the orbit with the help of a 'Proton-M' carrier rocket is considered.