Table of contents

The nonlinear dynamics of solid-state ring lasers with the homogeneously broadened luminescence line is studied upon periodic modulation of their parameters. The main temporal, spectral, and phase characteristics of counterpropagating waves are considered and non-stationary lasing regimes are classified.

The development of an IR terawatt Cr : forsterite femtosecond laser system with a pulse energy of 90 mJ and a pulse duration of 80 fs is reported. The laser system is assembled using Russian components only and has no analogues in the world.

An efficient reflecting coating made of a MIRO foil with an oxide layer is fabricated, which enhances the reflection of radiation of pump lamps in the head of a high-power neodymium laser and allows a gain g₀=5×10^-2 cm^-1 to be achieved.

The spatial and energy characteristics of radiation from a pulsed Nd³⁺ : YAG laser transversely pumped by laser diode arrays are studied experimentally by varying the resonator parameters. The differential efficiencies of the laser for multimode and close to single-mode free running lasing were measured to be 48 % and 40 % — 42 %, respectively.

Five new emission lines in the wavelength range of 70 — 140 μm are obtained from a CH₃OH submillimeter laser pumped by high-power periodic (500 Hz) quasi-stationary 70-μs pulses from a CO₂ laser. The wavelengths (with an error of 0.5 %), the threshold pump powers, and the optimal pressure are measured. It is shown that no saturation is present at pump powers of 1000 — 3000 W.

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L^-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm^-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.

The low-temperature laser plasma at the surface of metal targets is experimentally investigated. Continuous spectra emitted from a laser plume are found to be similar for targets consisting of the elements of the same subgroup of the Mendeleev periodic table. The similarity manifests itself both in the dependence of the emission intensity on the external pressure and in the structure of absorption bands related to a fine-dispersed phase existing in the peripheral regions of the plume.

The spatial self-organisation of a defect generation wave (DGW) in laser-excited crystalline semiconductors and dielectrics is considered. It is shown that due to the elastic crystal anisotropy, for a Gaussian intensity distribution of exciting laser radiation, the DGW is focused along the crystallographic axes, resulting in the production of optical damage 'stars'.

The parameters of laser ablation of channels in steel are studied in a wide range of nanosecond pulse repetition rates f (5 Hz ≤ f ≤ 200 kHz). It is found that for f ≥ 4 kHz, the results of ablation in air are identical to those obtained under the action of single laser pulses in vacuum. The experimental data as well as the estimates of the parameters of laser plasma and the gas environment in the region of the laser action lead to the conclusion that there exists a long-lived region of hot rarefied gas, known as a fire ball in the theory of explosions. The emerging rarefaction reduces the screening effect of the surface plasma formed under the action of subsequent pulses. This makes it possible to use lasers with a high pulse repetition rate for attaining ablation conditions close to the conditions in vacuum without complicating the technology of microprocessing by using vacuum chambers and evacuating pumps.

The propagation of laser radiation through a layer of a highly-scattering medium (HSM) is considered on the basis of two theoretical models: a nonstationary axial (two-flux) model and a nonstationary diffusion model. Analytic expressions for the temporal distributions of the photons of an ultrashort laser pulse transmitted through the HSM are presented. Experimental temporal distributions are used to obtain the parameters of models corresponding to an HSM, to determine the theoretical temporal distributions, and to compare them with the experimental curves. These two theoretical models are compared quantitatively for the first time. Their advantages and drawbacks that must be considered in the development of HSM transmission optical tomography are pointed out.

Variation in the correlation function of light multiply scattered by a random medium was observed with increasing the incident beam power. The light-induced motion of microparticles in suspension, caused by a high-power laser radiation, serves as an additional factor in the decorrelation of the scattered light. The experimental data are in good agreement with the results of theoretical analysis.

Based on the path-integration technique and the Metropolis method, the original calculation scheme is developed for solving the problem of light propagation through highly scattering objects. The elimination of calculations of 'unnecessary' realisations and the phenomenological description of processes of multiple small-angle scattering provided a drastic increase (by nine and more orders of magnitude) in the calculation rate, retaining the specific features of the problem (consideration of spatial inhomogeneities, boundary conditions, etc.). The scheme allows one to verify other fast calculation algorithms and to obtain information required to reconstruct the internal structure of highly scattering objects (of size ∼1000 scattered lengths and more) by the method of diffusion optical tomography.

The shifts of centres of nonlinear absorption and dispersion resonances in lasers with an internal absorbing cell are described. The shifts are caused by parasitic reflection of light from an intracavity plate and oscillate depending on the plate position. It is shown that this reflection leads to losses oscillating depending on the plate position. The main reasons of shifts in this case are frequency modulation used for laser frequency stabilisation and the curvature of the gain line in the two-mode regime. The results of a model experiment agree with theoretical estimates.

Optical phase locking of a diode laser to a mode of a femtosecond optical comb has been achieved with a system that combines the advantages of analog and digital phase detectors. Low noise and fast response are combined with a broad phase range and lock reliability. Details of the circuit are illustrated, and properties of different phase detectors in view of optical frequency measurements are discussed.

Temperature-noncritical third harmonic generation is studied theoretically and experimentally in an LBO crystal by compensating for the temperature-induced deviation of the phase-matching direction due to thermal strains in the crystal. The width of the phase-matching temperature curve obtained experimentally in a 14.1-mm-long LBO crystal for the third harmonic generation of the 1.064-μm radiation is 73 °C.

The results of the study of narrow laser tracks in soap films with the divergence below the diffraction-limited value are presented, and the mechanism of formation of narrow channels (spatial polariton solitons) based on laser dielectrophoresis in films is proposed.

The nonlinear transmission of light by single-wall carbon nanotube suspensions in D₂O at a wavelength of 1.54 μm is studied. For the 250-ns probe pulse and the 40-MW cm^-2 maximum intensity of radiation incident on a cell, the decrease in the absorption coefficient was 3.6 cm^-1 while the absorption coefficient in a weak field was 17 cm^-1. Q-switching and self-mode locking were obtained in a pulsed Er³⁺ : glass laser by using a cell with the nanotube suspension as a passive filter.

The results of numerical calculations of a fibre Raman amplifier pumped by continuous-spectrum radiation are presented. It is shown that the Raman gain flatness better than 0.1 dB can be achieved in the spectral region between 1528 and 1599 nm at the average gain of 7.7 dB, and the gain flatness of 0.042 dB in the case of the zero average small-signal gain in a 25-km SMF-28 fibre pumped by the 1-W and 364-mW backward radiation, respectively. Different variants of the approximation of the found optimal pump spectrum by a combination of four discrete radiation sources with broadened spectral lines are studied.

The effect of heating on the optical properties of Yb³⁺-doped fibres is studied. It is shown that the lasing efficiency of fibre lasers depends on the fibre temperature, the type and extent of the effect being substantially dependent on the laser wavelength. It is proposed to use fibre heating to increase the efficiency of lasers emitting in the 1.15 — 1.2-μm region.

The effect of properties of metal surfaces on the colour of their images obtained with a 510.6/578.2-nm copper vapour laser projection microscope is studied. The metal surfaces were exposed to laser radiation polarised by 99 % in the horizontal plane. Radiation used for surface imaging is predominantly polarised in the vertical plane and is coupled out of the resonator in the direction perpendicular to its optical axis. It is found that the ratio of laser radiation powers at wavelengths 510.6 and 578.2 nm determining the image colour is dependent on the total reflection coefficients, the curvature, and statistical characteristics of the surface roughness.

The problem of ion extraction from plane and cylindrical plasma layers located respectively between the plates and coaxial cylinders of a capacitor in laser isotope separation is considered. Simplified analytic models and numerical calculations within the framework of one-dimensional two-fluid hydrodynamics are used. The ion current to the cathode is shown to be adequately described by the three-halves power equation in which the distance of the plasma bunch boundary from the cathode is the electrode separation and the voltage drop across the capacitor plates serves as the voltage difference. The results of calculations are in qualitative agreement with experimental results.