Table of contents

The results of experimental and theoretical studies of the optical properties of globular photonic crystals – new physical objects having a crystal structure with the lattice period exceeding considerably the atomic size, are presented. As globular photonic crystals, artificial opal matrices consisting of close-packed silica globules of diameter ∼200 nm were used. The reflection spectra of these objects characterising the parameters of photonic bands existing in these crystals in the visible spectral region are presented. The idealised models of the energy band structure of photonic crystals investigated in the review give analytic dispersion dependences for the group velocity and the effective photon mass in a globular photonic crystal. The characteristics of secondary emission excited in globular photonic crystals by monochromatic and broadband radiation are presented. The results of investigations of single-photon-excited delayed scattering of light observed in globular photonic crystals exposed to cw UV radiation and radiation from a repetitively pulsed copper vapour laser are presented. The possibilities of using globular photonic crystals as active media for lasing in different spectral regions are considered. It is proposed to use globular photonic crystals as sensitive sensors in optoelectronic devices for molecular analysis of organic and inorganic materials by the modern methods of laser spectroscopy. The results of experimental studies of spontaneous and stimulated globular scattering of light are discussed. The conditions for observing resonance and two-photon-excited delayed scattering of light are found. The possibility of accumulation and localisation of the laser radiation energy inside a globular photonic crystal is reported.

Lasing and discharge characteristics of a nitrogen laser pumped by a transverse discharge from a generator with an inductive energy storage and a semiconductor current interrupter are investigated experimentally. A numerical model is proposed and the operation of a nitrogen–electronegative gas mixture laser is simulated. It is shown both theoretically and experimentally that admixtures of electronegative gases make it possible to control the laser pulse shape at the C³Π_u – B³Π_g transition of nitrogen. Laser pulses at a wavelength of 337.1 nm, consisting of two peaks, as well as rectangular pulses of duration 40–50 ns, are obtained in mixtures of nitrogen with NF₃ and SF₆ due to an increase in the electron attachment coefficient and an increase in the electric field. The output UV energy is ∼25 mJ.

Lasing parameters of a mixed Nd³⁺:Gd_0.7Y_0.3VO₄ vanadate crystal emitting at the 913-nm ⁴F_3/2–⁴I_9/2 laser transition are studied. The output power of up to 600 mW was obtained upon longitudinal diode pumping for the absolute and slope laser efficiencies of ∼13% and ∼17%, respectively.

The effect of a weak optical feedback on the power and spectral parameters of light-emitting modules based on near-IR quantum-well superluminescent diodes (SLDs) is studied. It is shown that even very weak parasitic feedback (k_fb < -30 dB) distorts the emission spectrum of high-power SLDs and noticeably reduces their output power.

Two models of metal–dielectric composite media are used to study the optical properties of their active (amplifying) components under conditions of compensation for the absorption of external electromagnetic radiation appearing due to the presence of metal inclusions. It is shown that the electrostatic approximation for describing the concentrated composite media (a metal nanosphere in a dielectric shell) and bulk composite media (a system of metal nanocylinders in a dielectric matrix) can be applied only in a small range of geometrical and optical parameters. Precise electrodynamic calculations give much smaller gains in the active component required to compensate for absorption, which can be useful for developing 'transparent' composite materials with unique optical properties or 'invisible' composite particles.

The absorption spectrum of a weak probe field in atomic vapours of rubidium, cesium and samarium in the presence of a strong field is studied theoretically. It is shown that away from resonance with an atomic transition, the probe radiation may have an anomalously high absorption coefficient (several times higher than the resonance value) in an anomalously narrow spectral range. The ultranarrow resonance in the probe-field absorption line wing is not related to any real transitions in the atom. Its position is determined by detuning from resonance frequency and by the strong-field intensity. It is shown that for identical frequencies of the strong and probe waves, the resonance can be recorded by using weak magnetic fields. The effect can be applied in the ultrahigh resolution spectroscopy and for precision measurements of the magnetic field strength.

The polarisation evolution of a ferroelectric crystal after its illumination by ultrashort laser pulses is described theoretically and numerically by using the microscopic pseudospin formalism. Parameters are found for which quasi-two-dimensional long-lived states can exist in ferroelectrics. For different initial conditions, the dynamics of bound states of the electromagnetic field and polarisation of the crystal is presented and properties of ferroelectrics with impurities and without them are compared.

A Faraday isolator with an aperture of 20 mm and compensation of thermally induced polarisation and phase distortions of laser radiation is fabricated and tested experimentally. A considerable improvement in the isolation degree over a traditional Faraday isolator is demonstrated. For radiation power up to 750 W, the isolation degree lies in the range 24–26 dB and is limited only by the quality of TGG crystals.

The operation of a narrowband filter based on a Fabry–Perot interferometer formed by two waveguide–grating mirrors is studied upon normal incidence of light. In this case, two counterpropagating travelling waves and coupled modes are excited in a corrugated waveguide, while only one mode is excited in the case of oblique incidence of light on the filter. It is found that in the case of a small gap between the mirrors, the reflection spectrum of the interferometer depends on the phase shift Δφ of one corrugation relative to the other. If light is incident normally on the interferometer, two or three lines appear in the transmission spectrum if Δφ ≠ 0 or Δφ ≠ π. The appearance of the additional resonances is attributed to symmetry breaking in the system. At large distances between the mirrors, the spectra at θ = 0 do not exhibit any peculiarities.

A general numerical method is proposed for constructing multilayer optical coatings without using the basic structure. The possibility of application of the theory of coupled waves for describing optical coatings with a large difference in the values of the refractive index is demonstrated. As design parameters, the coefficients of harmonic expansion of the required functions n(x) are used, which makes it possible to produce local variations in a certain spectral region. The method is quite pictorial. An example of application of this method for calculating a broadband divider is considered.

Two electrooptical switches for nonpolarised narrow beams from fibre laser and luminescent sources are considered. Requirements for crystals, the accuracy of their thermal stabilisation, and tolerances for their manufacturing and adjustment are estimated from the point of view of the maximum switching contrast. A switch based on two LiNbO₃ crystals with a control half-wave voltage of ∼270 V, connected with an isotropic single-mode fibre, is tested. It is shown that errors in the adjustment and manufacturing of crystal phase elements can be compensated by a weak controllable heating of one of the crystals.

The effect of various technological factors like the direction of crystal growth [(100) or (101)], acidity of the mother solution, growth rate, degree of filtration of the mother solution, purity of the starting raw material, specially introduced impurity (Pb), as well as after-growth thermal annealing, on the optical breakdown threshold of KDP crystals grown by the technique of rapid growth of profiled crystals is studied. It is shown that by using initial high-purity salts and fine filtration of solutions followed by after-growth annealing, it is possible to increase the optical breakdown threshold of profiled rapidly grown KDP crystals to values corresponding to the requirements of modern laser designs.

Stimulated Brillouin scattering (SBS) of single-frequency radiation in an AllWave™ telecommunication fibre and a phosphosilicate fibre is studied. The frequency shift and stimulated Raman gain are measured. The emission spectrum of a phosphosilicate Raman fibre laser is studied in the near-threshold regime. It is shown that SBS does not broaden the output emission spectrum of the Raman laser.

The aerosol backscattering coefficient β_π in a surface atmospheric layer is calculated at the emission lines of NH₃ and CO₂ lasers (9–13.5 μm). It is shown that the coefficients β_π at the emission lines of an NH₃ laser (11–13.5 μm) are comparable with the coefficients β_π at the emission lines of a CO₂ laser near 10.6 μm. The dependence of β_π on the humidity and type of aerosols is studied. It is also shown that the coefficient β_π in a surface atmospheric layer at the lasing of an NH₃ laser varies from 10^-10 to 7×10^-9 cm^-1 sr^-1. The lidar aerosol ratio is calculated as a function of the mean aerosol radius. It is found that this ratio is independent of the particle size for aerosol particles of radius exceeding 40 μm for the 11.7-μm aP(4,0) line of the ammonia laser.