Table of contents

The first single-mode cw laser with a Cr⁴⁺-activated forsterite crystal, pumped by radiation from a single-mode neodymium fibre laser, is described. The fibre laser is pumped by radiation from an array of semiconductor laser diodes. The Cr⁴⁺ : Mg₂SiO₄ laser radiation is tunable in the wavelength range 1.21–1.29 μm. The maximum output power at the λ = 1.24 μm wavelength is 150 mW. Lasers with active media containing Cr⁴⁺ ions, pumped by fibre-laser radiation, are promising as pump sources for fibre Raman amplifiers operating at λ = 1.3 μm.

An investigation was made of the radiation strength of GaAlAs—GaAs and InGaAsP—InP semiconductor lasers. This strength fell with increase in the laser emission wavelength. The highest radiation strength was observed for semiconductor lasers emitting at the wavelength of 0.85 μm.

An experimental investigation was made of a Ti : sapphire laser with active mode locking. The dependences of the duration of the output pulses, of their amplitude, and of their profile on the deviation of the cavity length from its optimal value, on the depth of loss modulation, and on the intracavity filter characteristics were determined. The stability of the laser parameters was measured and a comparison was made with self-starting mode locking based on the Kerr nonlinearity. The dependence of the position of a pulse in the transmission window of the mode locker' on the control parameters of the laser was obtained for the first time.

Highly efficient and practically continuous (with an off-duty factor less than 50) operation of an LiF:F₂^- colour-centre laser was observed when it was pumped by radiation from neodymium lasers with an average output power 0.2 —1.5 W. The use of an Nd³⁺ : YLiF₄ pump laser emitting at a shorter (1047 nm) wavelength made it possible to reduce the peak value of the threshold pump power to 10 W. Tunable operation of the LiF : F₂^- laser was achieved in the spectral range 1.07–1.27 μm and the efficiency at the maximum of the tuning curve reached 32%.

Experimental and theoretical investigations were made of the excitation and emission from a high-power HF laser pumped by a nonchain chemical reaction initiated by a radially converging electron beam. The distribution of the specific radiation energy in the output beam was determined and the distribution of the input energy over the laser chamber cross section was calculated for various gas mixtures. The space-charge field influenced the input energy distribution. The output radiation energy of a mixture of the SF₆ : H₂=8 : 1 composition was ∼115 J at a pressure of 0.45bar when the active volume was ∼30 litres, the efficiency relative to the input energy was ∼7%—8%, and the distribution of the radiation energy over the output beam cross section was relatively uniform. For the same input energy, because of the high density of SF₆, a pressure jump in SF₆— H₂(D₂) mixtures resulting from the combined effect of the electron beam injection and the chemical reaction was several times less than in active mixtures of exciplex lasers.

An experimental investigation was made of the optical quality of the active media of cw chemical HF lasers delivering powers from 20 to 400 kW. An original method based on lateral-shearing interferometry was proposed. The investigation was concentrated on small-scale periodic inhomogeneities resulting from the design features of the nozzle arrays.

An investigation was made of several relationships governing excitation transfer in Cr—Yb—Er phosphate glasses. The activator concentrations were optimised. A new LGS-KhM erbium-doped laser glass and its modifications characterised by a low thermal expansion coefficient, an enhanced thermomechanical strength, and a high chemical stability were developed. Under free-running conditions the differential efficiency was 2.6% at the threshold pump energy of 5 J reached in active elements 2.5 mm in diameter and 35 mm long. Under Q-switching conditions a pulse of 30 ns duration and of 10 mJ energy was emitted when the pump energy was 6 — 7 J.

The spectral and luminescence parameters of neodymium-activated GLS1 glass and the lasing parameters of active elements made of this glass were determined. The scatter of these parameters was found by a statistical analysis of the results of measurements of the properties of glasses prepared at different times and under different conditions.

An investigation is made of the feasibility of separating a train of attosecond short-wavelength pulses from a combined field of high-order harmonics. Semiclassical and quantum-mechanical theories of the generation of high-order harmonics are used to consider the problem of minimum duration of a pulse which can be generated by summing the fields of several adjacent harmonics near a harmonic-generating gas layer. A study is made of the spatial structure of the field of harmonics generated in a thin layer subjected by a Gaussian laser beam. It is shown that harmonics of different orders have different divergences and that they focus at different distances when generated in a converging beam. This effect may be utilised to separate harmonics of specific orders, particularly in the generation of attosecond pulses. High-intensity fundamental-frequency and third-harmonic radiations should be suppressed by other methods. Calculations predict that pulses of duration down to 90 as and of intensity comparable with that of the third harmonic can be generated.

A Mach—Zehnder fibre interferometer, based on two photoinduced long-period gratings, was used in an investigation of the dynamics of the refractive index Δn_ind induced in the core of a germanosilicate optical fibre by different types of UV irradiation. It was found that the value of Δn_ind could be approximated satisfactorily by a power-law function of the radiation dose at all the investigated wavelengths. A comparative analysis of the dynamics of the refractive index in the case of singlet and triplet photoexcitation of germanium oxygen-deficient centres showed that the dominant mechanism of the change in the refractive index by low-intensity continuous UV irradiation was transformation of these centres from an excited triplet state.

Theoretical and experimental investigations have shown that parasitic stimulated Brillouin scattering may appear because of loop-type feedback in amplifying neodymium-glass elements.

An experimental investigation was made of the feasibility of stimulated Brillouin scattering during an XeCl laser pump pulse of τ_1/2=80 ns duration. The duration of a Stokes pulse was found to depend on the absorption in the nonlinear medium employed. When this medium was heptane, the Stokes signal duration was τ_1/2 ∼ 15 ns, but for SF₆ it was τ_1/2 ∼ 70 ns. The most probable reason for the short duration of the Stokes signal was the loss of phase matching in the scattering process.

Experimental and theoretical investigations were made of the excitation of surface electromagnetic waves in a corrugated thin metal film. The process was found to be accompanied by a specific change in the reflection coefficient. It was shown that the excitation of surface electromagnetic waves in a thin metal film may be used in sensor applications.

Experimental and theoretical investigations were made of a nonlinear response to loss modulation in a CO₂ laser with detuning of the emission frequency from the centre of a lasing line. The nature of the response depended fundamentally on the ratio of the modulation frequency to the main resonance frequency of the laser. The experimentally observed asymmetry of the amplitude—detuning characteristic was attributed to a change in the refractive index as a result of loss modulation. The presence of peaks on this characteristic could be used to stabilise the emitted radiation at a frequency detuned from the lasing line centre.

An automatically controlled system for stabilisation of the output power of an Nd : YAG laser with intracavity frequency doubling was constructed. This system applied to an industrial laser of the LG-402A type. Active stabilisation of the output radiation was performed by personal-computer control of the pump current and of the thermal conversion regime in the nonlinear element. Algorithms developed for control of the output radiation parameters make it possible to avoid the use of a probe perturbation and to achieve a relative instability of less than 0.5% for the integral intensity of the second-harmonic radiation.

A system for stabilisation of the intensity of single-mode He—Ne laser radiation was developed and constructed. The system is based on the intracavity interaction of the fields (autodyne effect). The radiation parameters are controlled by returning some of the output radiation back to the laser cavity. A phase self-locking system makes it possible to eliminate the stochastising influence of the backscattered radiation and also to suppress by more than one order of magnitude the intrinsic low-frequency fluctuations of the laser radiation intensity.

The optical beat spectrum of a three-mode jet dye laser was investigated. When the modes became nonequidistant the combination tones shifted from their calculated frequencies, the intensity became modulated at the frequency of the deviation from the equidistant distribution, and the generated modes acquired side frequencies. The beat spectrum showed not only splitting of the fundamental frequencies, but was also enriched with components of frequencies which were single and double multiples of the difference between the intermode frequency intervals. Technical fluctuations of these differences, associated with an instability of the optical length of the empty cavity, were correlated and were compensated in the low-frequency difference components.

It is shown that simultaneous locking of longitudinal and transverse modes is possible in a semiconfocal cavity. A laser with a high repetition rate (10–100 MHz) then emits alternately strongly and weakly diverging pulses. A laser operating in this way may be useful in various sounding and ranging applications. A laser with such locking is a wide-aperture device with a large volume of the active medium.

A resonant process of spontaneous scattering of photons on a counterpropagating beam of relativistic electrons, which acquire the properties of harmonic oscillators in a static magnetic field, generates with a high quantum efficiency a monochromatic directional intense beam of hard photons.

A new approach is proposed to investigate the roughness of concave surfaces on the basis of the whispering gallery effect in the x-ray range. A computer simulation of two possible experimental setups showed that it should be possible to extract information on the statistical properties of the surface roughness from measurements of the angular distribution and power of an x-ray beam which bends along a concave surface.

The method of extended crossing beams was used to investigate inelastic collisions of copper atoms with slow monokinetic electrons. The excitation cross sections of 160 spectral lines of the copper atom, located in the range 202–810 nm, were determined at the exciting electron energy 50 eV. Seventy-nine optical excitation functions were found in the electron energy range from the threshold to 250 eV. For the spectral series 4p²P⁰—ns²S and nd²D the dependences of the cross sections on the principal quantum number of the upper level were of the power-law type, but strong perturbations were observed for the 4s²²D—np²P⁰ series. The results obtained were used to calculate the excitation cross sections of 19 energy levels of the copper atom. The results were compared with those obtained by other authors.

The problem of separation of the alignment-error signals, resulting from perturbations of separate mirrors, is considered for a laser gravitational-wave interferometer representing a full combined Fabry—Perot—Michelson scheme with radiation recycling. The Anderson method framework is used to show that such separation can easily be attained subject to some restrictions imposed on the recycling-cavity finesse.

An investigation is reported of the correctness of reconstruction of the temporal profile of a single ultrashort light pulse by the cross-correlation method. A numerical estimate is given of the temporal resolution of this method.