Table of contents

The spectral and lasing properties of a new nanostructure F₂^-:LiF colour centre ceramics are studied and compared with those for single crystal samples. The slope lasing efficiency up to 26% is achieved in the diode-pumped F₂^-:LiF laser ceramics.

Continuous wave lasing in a Cr²⁺:CdSe crystal is obtained for the first time. The Cr²⁺:CdSe crystal pumped by a 1.908-μm thulium fibre laser generated 1.07 W at 2.623 μm with the quantum slope efficiency with respect to the absorbed power equal to 60%.

A hybrid subpicosecond system based on a Yb:KYW laser and a Yb fibre amplifier made by using the GTWave technology is studied. The system pumped by the 980-nm, 12-W cw radiation emits 0.9-ps, 40-nJ pulses at a pulse repetition rate of 100 MHz and an average power of 4 W. The central emission wavelength of the system can be tuned in the pulsed regime from 1038 to 1053 nm and from 1030 to 1070 nm in the cw regime. The gain of the Yb fibre GTWave amplifier is measured for the first time within the tuning range of the Yb:KYW laser.

Superluminescent diodes based on a single-layer quantum-well (GaAl)As heterostructure with the ridge active channel of width 25 μm are studied. At moderate levels of the injection current density and radiation load on the output facets the output cw power above 200 mW is obtained. The efficiency of coupling radiation into a standard multimode fibre is 75%.

The spectra of spontaneous emission accompanying the generation of femtosecond superradiant pulses in GaAs/AlGaAs heterostructures are studied. It is clearly demonstrated that spontaneous emission spectra of electron–hole pairs, which have been left in the semiconductor after the formation of a coherent collective e–h state, correspond to the strong overheating of carriers. This phenomenon can be explained by the effect of dynamic cooling and nonequilibrium condensation of collectively paired carriers at the bottoms of the bands during the superradiant emission, which was observed earlier.

A new method for frequency control of an external cavity diode laser without direct modulation of the injection current is proposed. The Pound – Drever optical heterodyne technique or the method of frequency control by frequency-modulated sidebands, in which an acousto-optic modulator operating in the Raman – Nath diffraction mode is used as an external phase modulator, can be employed to obtain error signals upon automatic frequency locking of the diode laser to the saturated absorption resonances within the D₂ line of cesium atoms or to the optical cavity resonances.

The influence of polarisations of counterpropagating waves on the dynamics of self-modulation oscillations of the first kind in solid-sate ring lasers is studied theoretically and experimentally. The characteristic features of amplitude and frequency characteristics of radiation and the spectra of relaxation oscillations appearing at different polarisations of counterpropagating waves are analysed. The obtained experimental results are well described by the vector model of a solid-state ring laser, which takes into account different polarisations of the ring resonator for counterpropagating waves.

The dynamics of continuum generation by a superpower ultrashort pulse in fused silica is numerically simulated taking into account photon ionisation. It is found that a high-intensity femtosecond laser pulse splits during its propagation into subpulses and subbeams. The emission spectrum is shown to broaden considerably both to the high- and low-frequency regions.

The stationary two-wave interaction in an optically uniaxial photorefractive crystal on a transmission photorefractive grating produced due to the photogalvanic or diffusion mechanism is considered. The possibility of the nonunidirectional amplification of a weak wave, which is consistent with a change in its polarisation state caused by the interaction, is shown. The conditions of the nonunidirectional energy exchange in Fe:LiNbO₃ and SBN crystals with the local and photorefractive responses, respectively, are determined.

The spectral dependences of absorption photoinduced in a pure bismuth titanium oxide crystal by 532-nm laser pulses are studied. It is shown that optical absorption in the crystal in the range from 492 to 840 nm increases with increasing exposure. The photoinduced absorption relaxes in the dark for more than 60 hours. A model of photoinduced absorption is proposed which assumes the population of two trap centres with the normal energy distribution law for the concentrations of electrons photoexcited from donors to the conduction band. This model well describes the spectral dependences of photoinduced absorption by using the average ionisation energies of the traps E₁ = 1.60 eV and E₂ = 2.57 eV. The model is used to estimate the increase in the photorefractive sensitivity of a bismuth titanium oxide crystal in the near IR region, which was earlier observed after exposing the crystal to visible radiation. It is predicted that the speed of response of dynamic holography devices based on BTO crystals exposed to green light can be increased.

The second harmonic generation in KDP and LiNbO₃ crystals exposed to tightly focused radiation from a Cr:forsterite laser is studied. The negative influence exerted on this process by a plasma produced due to multiphoton ionisation in the focal region at laser pulse intensities above 10¹³ W cm^-2 is discussed.

It is found experimentally for the first time that the initial phase modulation of femtosecond pump pulses considerably affects the degree of coherence of the short-wavelength radiation of a supercontinuum with pronounced soliton structures in the spectrum generated in a microstructure fibre. The long-wavelength soliton radiation preserves the complete coherence upon changing the phase modulation of the pump pulse despite considerable variations of the carrier frequency of solitons. The maximum width of the supercontinuum and the maximum degree of coherence of its short-wavelength radiation are achieved for small positive values of the phase modulation parameters.

Nongraphitising ablation of the surface of a natural diamond single crystal irradiated by nanosecond UV laser pulses is studied experimentally. For laser fluences below the diamond graphitisation threshold, extremely low diamond etching rates (less than 1nm/1000 pulses) are obtained and the term nanoablation is used just for this process. The dependence of the nanoablation rate on the laser fluence is studied for samples irradiated both in air and in oxygen-free atmosphere. The effect of external heating on the nanoablation rate is analysed and a photochemical mechanism is proposed for describing it.

High-speed interference filming is used to study the dynamics of development of the change region of a surface vapour–plasma formation under the action of laser radiation with a power density up to 10⁷ W cm^-2 and a pulse duration of ≈1 ms on polymethyl methacrylate samples of thickness up to 1 cm. Experiments show that damage region is mainly produced due to a thermal mechanism along with the possible effect of the emerging elastic vibrations. It is also shown that the damage takes place predominantly at the initial stages of the process (up to 100 μs) due to shielding of the sample by a vapour–plasma cloud and scattering of radiation from the liquid-drop phase.

An experimental technique for obtaining nanostructures in the field of high-power laser radiation at the surface of carbon materials is developed. A specific feature of this technique is the formation of liquid carbon inside the region of laser action in the sample exposed to radiation in air at a pressure of ≈1 atm. Several types of nanostructures (quasi-domains and nanopeaks) are detected in the laser cavern and beyond the range of laser action. Mechanisms of formation of such structures are proposed. The formation of quasi-domains is related to crystallisation of the melt. The nanopeak groups are formed outside the laser action region during the deposition of hot vapours of the material escaping from this region. The dependences of the variation in morphological properties of the nanostructures on the duration of laser action and the radii of typical cavern zones on the laser radiation power are obtained.

Metal films of heat-removing elements deposited by magnetron sputtering are modified by radiation from a diode-pumped pulsed solid-state Nd:YAG laser to improve the output parameters of high-power laser diodes.

The interaction of a gas jet (He, Ne, Xe) with the incident laser plasma from a solid target [B, (CH₂)_n, (CF₄)_n] removed by ≈1 cm is investigated. Line spectra arising from the charge exchange of multiply charged plasma ions with rare-gas atoms are recorded in the multiply charged ions–gas interaction region. The ratios between the partial cross sections of the charge exchange with the production of these ions in excited states are determined from the relative intensities of the Balmer series transitions in BV and CVI ions. These results are compared with theoretical data.

A method of phase conjugation for formation of non-Gaussian light beams with the specified transverse intensity distribution in waveguide quasi-optical resonators is described. The method is based on the correction of the phase of the fundamental resonator mode by changing the shape of one of the reflectors. The possibility of producing beams with the super-Gaussian and doughnut-like intensity profiles in a waveguide resonator with an aspherical mirror is shown theoretically. The region of geometrical parameters of the resonator is found for which the difference between the phase functions of aspherical and convex spherical resonators is small. The existence of beams with the super-Gaussian intensity profile at the output of a waveguide submillimetre (λ = 0.4326 mm) resonator with a convex spherical mirror is confirmed experimentally.

A Fe²⁺:ZnSe laser emitting in the spectral range between 3.77 and 5.05 μm is used for the first time for intracavity laser spectroscopy. The intracavity absorption spectra of methane in the 4.1-μm region are recorded at different instants of lasing (0–80 μs) and the dynamics of spectral holes during lasing is investigated. It is found that an intracavity absorption signal linearly increases with time during lasing in the time range from 0 to 80 μs, which provides the effective absorption length up to 24 km.

It is shown that laser photothermal radiometry (LPTR) in combination with laser beam scanning within the instantaneous field of view of a single-element photodetector can be used to develop a scanning thermal emission microscope. An expression is derived for estimating its temperature resolution. The results of calculations are presented and the factors influencing the spatial lateral resolution of the technique and the time of image formation with the help of an acousto-optical deflector are analysed.