Table of contents

A tunable colour-centre laser was used in a study of Doppler-free saturated absorption resonances at the R lines of the ν₃ band of the methane molecule (λ = 3.2–3.3 μm). The spectral resolution was 300 kHz for a configuration with an intracavity absorption cell. The laser is suitable for the investigation of any of the R and Q lines of the ν₃ methane band, and the long-wavelength limit of the tuning range reached the P(2) line.

A detailed account is given of self-modulation and relaxation oscillations in single-mode solid-state ring lasers. A classification of self-modulation lasing regimes in such lasers is proposed. The results are given of theoretical and experimental investigations of the existence conditions and stability of various self-modulation regimes, of transient processes, and of relaxation oscillations in these regimes. The main dependences of the characteristics of self-modulation and relaxation oscillations on the laser parameters are considered. The interaction of self-modulation and relaxation oscillations, and the conditions for the appearance of dynamic chaos are discussed.

A waveguide N₂, laser was used to pump rhodamine 6G, the most widely used laser dye. The energy characteristics and the spatial structure of the radiation were investigated. In a nonselective cavity the dye laser emitted pulses of 200 W power and of 2 ns duration. The efficiency of conversion of the pump radiation was 3.5%.

InGaP/GaAs/InGaAs heterostructures were grown by MOCVD hydride epitaxy at atmospheric pressure. They were used in injection semiconductor lasers emitting at 0.92–1.02 μm. The output power of one cleaved facet was up to 750 mW when the width of the active stripe was 100 μm. The external differential quantum efficiency reached 42%. Linear laser arrays, consisting of five emitting stripes, were capable of supplying radiation powers up to 2 W continuously and were suitable as pump sources for solid-state lasers. Single-mode narrow-stripe (5 μm) lasers had an output power up to 25 mW from one cleaved face. Additional transverse modes were emitted when the output power was increased to 30 mW. The characteristic features of the technology used in fabrication of these lasers are described.

It is shown theoretically that an lf maximum in the noise spectrum of travelling-wave ring solid-state lasers is a manifestation of beats between the wave generated and a regeneratively amplified spontaneous radiation propagating in a direction along which there is no lasing.

The spectral characteristics of the radiation emitted by a Raman laser with intracavity frequency conversion were investigated. This laser was found to suffer from frequency chirp both of the pump radiation and of the Raman frequencies. The integral width of the spectrum at the pump and Raman frequencies could exceed 1 cm^-1.

A compact sealed-off metal-ceramic CO₂ rf-excite laser with an output power of 30 MW was constructed. The laser is intended for medical and industrial applications. It utilises a discharge structure of the gap type and hybrid unstable—waveguide cavity with propagation of radiation both in free space and in a waveguide.

Lasing was achieved in a holographic laser with a distributed feedback (DFB) based on an epoxy polymer matrix activated with rhodamine 6G. The temperature sensitivity of the emission wavelength was one-thirtieth of the sensitivity of a DFB laser with a liquid dye solution. Excitation with the second harmonic of a YAG : Nd³⁺ laser, in the form of pulses of 15 ns duration and 2 mJ energy, made it possible to achieve an efficiency of 14% for this solid-state laser emitting at the wavelength of 587 nm when the spectral line width was 0.01 nm.

A new type of polarisation-independent modulation of laser radiation with the aid of the acoustooptic interaction is considered. This modulation is based on the use of the properties of reflecting surfaces and of the acoustooptic properties of gyrotropic media. It is shown that polarisation-independent modulation of monochromatic radiation can always be realised over a wide range of acoustic wave frequencies. Three types of polarisation-independent modulation of two-frequency Ar laser radiation with the wavelengths 0.488 and 0.5145 μm are described. Experimental results are given for modulation in which the properties of a TeO₂ single crystal are used in a geometry ensuring the maximum diffraction efficiency. Polarisation-independent diffraction of the two-frequency Ar laser radiation by an acoustic wave of 58 MHz frequency is reported.

The radiation generated in a submillimetre HCN laser with an amplitude-anisotropic resonator cavity was elliptically polarised. The ratio of the orthogonal components was 20–22 dB. The ellipticity was observed for homogeneous and inhomogeneous discharge gaps.

An analysis is made of effective mode locking in continuously operating solid-state lasers by modulators based on second-harmonic generation. A new type of modulator is proposed in which a radiation field replica, attenuated as a result of harmonic generation, is subtracted interferometrically from the field. In principle, the proposed modulators can ensure more effective mode locking because of optimisation of the initial modulator transmission and because the intensity derivative of the transmission is used. Self-consistent solutions of a system describing continuous generation of ultrashort pulses are obtained and are shown to agree with the results of an analysis of the lasing dynamics based on the fluctuation model.

A numerical calculation is reported of the reflection coefficient of a plane electromagnetic wave incident on a multilayer asymmetric planar metal—semiconductor structure, which forms a Schottky barrier at the interface. The slope of the modulation characteristic of the reflection coefficient is calculated for the case when the thickness of a depletion layer in the contact region is controlled by an external voltage. This slope is shown to be considerably less than the value reported by other authors. An explanation is given of this discrepancy and methods for increasing the slope of the modulation characteristic are suggested.

A theoretical investigation is reported of the suppression of noise waves in a thin-layer mutual conjugator. The methods of matrix and wave optics are used to show that the displacement of thin layers from the exact image planes in the direction towards a lens results in mutual phase conjugation of Gaussian beams when the self-oscillation threshold is exceeded slightly.

A numerical analysis is used to formulate the conditions for the manifestation of bistable reflection of a quasimonochromatic light pulse from a thin layer of a resonant medium with nonlinear refraction. The duration of the light pulse is assumed to be less than the phase relaxation time of the nonlinear material. The nonlinearity is due to the existence, in the energy structure of the active atoms, of transitions adjacent to resonances.

Picosecond pulses of the fifth harmonic of a YAG : Nd laser were used to study nonlinear absorption in fused quartz and in water at the wavelength of 212.8 nm. The two-photon absorption coefficients of quartz and water were determined. In the approximation of the Gaussian shape for the laser pulses these coefficients were (7.5 ± 0.4)×10^-10 and (3.2 ± 0.3)×10^-10 cm W^-1 for quartz and water, respectively.

It is proposed to generate broadband radiation by stimulated Raman scattering from rotational levels of atmospheric nitrogen under conditions of a strong parametric coupling with the pump radiation provided by a high-power two-frequency neodymium laser. Various ways of constructing such a two-frequency laser are proposed. It is shown that up to 20 Raman components can be generated if the intensities of the lines, separated by the 76 cm^-1 frequency of the S₀(8) transition in nitrogen, are 2 GW cm^-2 and the length of the air path is 20 m.

A theory of cascade generation of the third harmonic in a laser cavity is developed in the constant intensity approximation. Changes in the phases of the interacting waves are taken into account. The efficiency of third-harmonic generation has a maximum in its dependences on the intensities of the pump and second harmonic. Optimal phase matching can considerably increase this efficiency.

A transient three-dimensional model is used in a numerical investigation of the spatiotemporal and spectral characteristics of a femtosecond pulse of 10¹⁴—10¹⁶ W cm^-2 intensity propagating in rare gases. It is shown that nonlinear defocusing caused by the ionisation of a gas may result in a 20-fold reduction of the peak intensity in the beam waist. The transverse distribution of the intensity beyond the waist is a ring with a minimum on the beam axis at a pressure of 1 bar and with a local maximum on the axis at 5 bar. The frequency spectra of such a pulse are in quantitative agreement with experimental data.

Current pulses were generated in the course of the polarisation of air ionised by ultraviolet radiation. The dependence of the current pulse duration on the air pressure had a maximum. The amplitude of the pulses depended quadratically on the intensity of the laser radiation with the wavelength of 266 nm; the amplitude increased when the pressure was reduced in the range 10–760 Torr.

An investigation of the polarisation properties of dielectric structures with a double-sided periodic relief is reported. A brief description is given of a method which can be used to calculate the dependences of the transmission by, reflection from, and losses in a dielectric film with a periodic surface relief on the thickness of this film, and on the wavelength and angle of incidence of light. A numerical calculation, confirmed experimentally, reveals that such structures exhibit polarisation-dependent abrupt changes in the transmission and reflection near certain wavelengths or film thicknesses.

An analysis is made of the operation of a three-channel correlator used in the determination of the time dependences of the intensities of single ultrashort laser pulses of arbitrary structure. The control channels of the correlator have switches based on the quadratic electrooptic effect. The fifth-order correlation function I⁽⁵⁾(τ₁, τ₂, τ₃, τ₄) with τ₁ = τ₂, τ₃ = τ₄ is recorded at the correlator exit. The proposed and analysed procedure for the processing of the recorded information makes it possible to determine the structure of an optical signal in the form I(t). The procedure is based on the conversion of the signal to the spectral representation and the use of the real part as well as of the derivative (with respect to the frequency ω₃) of the imaginary part of I⁽⁵⁾(ω₁, ω₃) when ω₃ = −ω₁.

A high-quality optical system with spherical surface, capable of focusing an x-ray laser beam into a 'line' (a rectantular strip with a large ratio of the sides), was developed. It is intended for x-ray laser investigations involving the ISKRA-4 facility.

Superimposed phase diffraction gratings were formed by an electron beam in amorphous arsenic sulfide (As₂S₃) films. The number of superimposed gratings was N = 2–10 and the angle of slant was π/N. The electron-beam-stimulated modulation of the refractive index n₁ = 10^-3—10^-2 of the superimposed gratings was studied as a function of the number of these gratings. The main factor which limited the number of mutually independent superimposed gratings was the limit of linearity of the response of the recording medium at the nodal regions where the total radiation dose was maximal.

A multichannel system for determining the time parameters of pulsed laser radiation, based on a fast streak camera with fibre-optic communication lines, is described. It is shown that the tautochronism of laser beams can be determined simultaneously in all the channels of the facility and the maximum error does not exceed 25 ps.

A lateral-shearing interferometer was used in an investigation of the profile of the wavefront of a high-power ISKRA-5 iodine laser with an aperture of 700 mm. The aberrations of the optical system and the profile of the front of a single pulse were determined.