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The propagation of electromagnetic pulses in Josephson structures is investigated theoretically. An analogy with interaction of light pulses with a twolevel medium is traced. Under certain conditions the propagation of electromagnetic radiation in a two-level medium and in a Josephson structure is described by the same wave equation.

Theoretical estimates of narrowing of the emission line of an injection laser with an external resonator are obtained for different mechanisms that determine the line width. If the width of a line emitted by a laser diode without an external feedback ("initial" width) is governed by phase fluctuations because of the spontaneous noise, then the width of a line emitted by an injection laser with an external resonator is a quadratic function of the line width of the resonator itself. However, if the initial width is determined by fluctuations of the refractive index of the active medium, then the same dependence is linear. It is shown that external resonator configurations used so far have not been optimal. Ways are suggested for introducing high-Q interferometers into the external part of a composite resonator of an injection laser, which should make it possible to reduce the width of the emission line of a laser with an external resonator to ~1–103 Hz without altering the dimensions. An analysis is made of the influence of a wide-band electronic circuit for automatic phase control (based on an external high-Q interferometer) on the emission spectrum of an injection laser. It is shown that the "natural" width of an emission line may be reduced by between four and six orders of magnitude if the proposed method is used.

Theoretical and experimental investigations were made of the scattering of surface electromagnetic waves at an interface between a metal and a liquid crystal in metal–insulator–metal–liquid crystal structures. Surface electromagnetic waves were created as a result of electron tunneling in the metal–insulator–metal part of a structure and these waves were scattered by a periodic inhomogeneity of the permittivity of the liquid crystal.

A calculation is made of the spectral density of the intensity of surface electromagnetic waves excited by the passage of a current across metal–barrier–metal tunnel structures when there are quantum potential wells inside the barrier. It is shown that quasilevels in these quantum wells give rise to narrow peaks in the spectrum of the excited surface electromagnetic waves and that the quantum efficiency of the excitation of such waves by tunneling electrons can reach unity. The peak positions can be controlled by altering the voltage across a tunnel structure.

It was shown theoretically that the use of a nonlinearly absorbing cell inside the resonator of a laser leads to a reduction in the width of the laser emission line by a factor of S in the case when apparatus-induced fluctuations are dominant, and by a factor of S2 for the case of natural fluctuations (S is the autostabilization factor). It was established experimentally that S reaches a value of ~ 25 in an injection laser with a nonlinearly absorbing cell containing cesium vapor, and that this enables one to improve substantially the monochromaticity of the radiation from injection lasers without increasing their dimensions.

An investigation is made of the noise aspects of measurements of laser frequencies using superconducting point contacts. It is shown that the thermal Nyquist noise makes no contribution to the line width of the intermediate-frequency signal and the contribution associated with the finite line width of klystron radiation may be reduced substantially.

A theoretical and experimental investigation was made of the high-frequency properties of Nb–Nb superconducting point contacts (SPC's) operating under nonequilibrium conditions with a high critical current Ic and low normal-state resistance RN. The possibility of using these contacts in raetrological applications in the near infrared was studied. On exposure of these SPC's to external radiation, current steps corresponding to the harmonics of the external radiation frequency were readily observed on their current-voltage characteristics at voltages exceeding the limiting value for niobium SPC's. In this case, the frequency was subject to a capacitative limitation. Frequency multiplication up to 8×1012Hz (~38μ) was observed at bridges having dimensions not exceeding 50 nm. Investigations were made of the dependences of the step-like structure of the current-voltage characteristics of SPC's on the external radiation power, and frequency. The dependences of the intermediate-frequency signal amplitude and width on the bias voltage and power of the external signals on exposure of SPC's to two radiation sources were also studied. A theoretical analysis showed that, in frequency multiplication and mixing by SPC's operated under nonequilibrium conditions, allowance must be made for the action of both the selfradiation and its harmonics on the SPC.

A theoretical analysis is made of the problem of obtaining a negative differential resistance in the currentvoltage characteristic of metal–barrier–metal–barrier–metal junctions and the feasibility of using these to develop a tunable oscillator is examined. Calculations are made of the maximum lasing power and gain.

Electromagnetic oscillations of 180 kHz frequency tunable in a range of 30 kHz were generated in a metal–barrier–metal–barrier–metal (MBMBM) structure characterized by a negative differential resistance. Such structures are potential tunable sources of electromagnetic radiation ranging from the radio to the optical frequencies.

A theoretical analysis is made of the feasibility of developing a tunable oscillator emitting stimulated radiation in the submillimeter and far infrared ranges utilizing systems of Josephson junctions. It is shown that under certain conditions, this system interacting with the resonator field can emit a power of ~10 mW.

A theoretical investigation is made of the interaction between an electron and a barrier in metal–barrier–metal junctions in a high-frequency electromagnetic field. Using the second harmonic as an example, it is shown that harmonic generation does not take place over the whole length of the metal wire but in a region near the barrier.

An investigation was made of the angular distribution of the luminescence emitted by a metal–barrier–metal (MBM) diode formed on a smooth substrate. The brightness of the p-polarized luminescence observed at an angle of 80° relative to the normal to the diode plane was 65 times higher than the intensity along the normal, whereas the s-polarized luminescence was 16 times greater. Calculations indicated that in the case of an MBM diode formed on a smooth substrate such an angular distribution in the case of the p-polarized component of the luminescence originating from decay of surface plasma oscillations at the insulator–metal interface may be governed not only by the interaction of plasmons with inhomogeneities of certain size of the metal (silver) film, but can also be influenced by the ratio of the permittivities of the media.

A study was made of light emitted as a result of decay of surface plasma oscillations in metal–oxide–metal structures. An absolute increase in the intensity of this light and its control were achieved by using a medium external to the metal film. This medium was a liquid crystal forming a domain structure in a static electric field. The arrangement provided a convenient means for investigating the processes of radiative decay of surface plasmons.

It is shown that a chemical oxygen-iodine laser (COIL) is a high power and highly efficient laser operated in a CW and a pulse-repetition regime. An active medium of this laser admits to realize a coherent amplification of high power pulses. Some features of the coherent amplification in such a medium and a feasible scheme of an experiment for obtaining of powerful pulses are considered.

An investigation was made of the mechanism of generation of oscillation modes in a resonator excited by a Josephson point junction or bridge. On the basis of a system of Maxwell's equations and material equations in the Fokker–Planck approximation expressions were derived for the amplitudes of the fundamental-frequency harmonics and for the number of harmonics with comparable amplitudes. It was shown that with an appropriate choice of junction parameters and excitation frequency, the number of harmonics may be ~103, the harmonics in this case falling within the optical band. Detailed experimental investigations were made of the nonlinear high-frequency properties of a superconducting niobium–niobium point junction in an external microwave field. Different operating conditions with frequency multiplication by the point junction were studied. Theory and experiment were compared. It was found that for frequency multiplication in the submillimeter band, a superconducting point junction operating under nonequilibrium conditions is potentially more useful than a conventional Josephson point junction.

An experimental investigation was made of the tunneling of particles in a microwave field. Depending on the normal resistance of superconducting point contacts, the tunneling could be accompanied by both absorption and emission or by just emission of microwave photons.

We present calculations of Auger carrier capture processes into self-assembled quantum dots. A strong dependence of the Auger capture rate on the size and geometry of the quantum dots is demonstrated.

Propagation, transmission and reflection properties of linearly polarized plane waves and arbitrarily short electromagnetic pulses in one-dimensional dispersionless dielectric media possessing an arbitrary space-time dependence of the refractive index are studied by using a two-component, highly symmetric version of Maxwell's equations. The use of any slow varying amplitude approximation is avoided. Transfer matrices of sharp nonstationary interfaces are calculated explicitly, together with the amplitudes of all secondary waves produced in the scattering. Time-varying multilayer structures and spatiotemporal lenses in various configurations are investigated analytically and numerically in a unified approach. Several new effects are reported, such as pulse compression, broadening and spectral manipulation of pulses by a spatiotemporal lens, and the closure of the forbidden frequency gaps with the subsequent opening of wavenumber bandgaps in a generalized Bragg reflector.

Self-assembled quantum dot laser with pump of lasing levels purely through Auger carrier capture is analyzed. Analysis shows that Auger processes can provide effective laser pumping and fast modulation at least up to 10 GHz.

An investigation was made of the influence of submillimeter radiation emitted by an HCN laser operating at a frequency νl = 891 GHz on a superconducting point contact made of Nb3Sn. Three steps of the electric current were recorded. The experimental results indicated that such a contact could be used for frequency multiplication up to 3 THz.

A description is given of a system for measuring small displacements. This system is based on the characteristics of the dynamics of emission from ring lasers associated with a redistribution of the energy between the counterpropagating waves. The minimum detectable vibration amplitude was ~10?18?10?19 cm and it was limited by fluctuations of the laser radiation intensity.

An increase in the efficiency of light emission (by over an order of magnitude) was achieved for plasma oscillations in a thin silver film of a gold–aluminum oxide–silver (Au–Al2O3–Ag) structure by altering the permittivity of a nematic liquid crystal adjoining the silver film.

An experimental study was made of the amplification of surface plasma oscillations due to a negative differential resistance of an Au–Al2O3–In2O3–Al2O3–In2O3–Al2O3–Ag structure resulting from resonance tunneling of electrons in a periodic potential field of a complex insulator barrier in this metal–barrier–metal structure.

A study was made of the influence of the technology used in the fabrication of a dielectric barrier on the luminescence spectrum of a metal–barrier–metal (MBM) diode. The barrier was formed by electron-beam sputtering or by ion implantation. Various methods of fabrication of the barrier layer affected the electrophysical characteristics, but not the spectral properties of tunnel MBM diodes. This confirmed that the plasma mechanism was the main reason for the luminescence of radiation by MBM diodes.

It is shown theoretically that a superconducting point contact placed in a resonator, and exhibiting both the Josephson nonlinearity and the nonlinearity characteristic of a metal–oxide–metal diode, can be used to multiply a microwave frequency right up to the optical range.

The luminescence of a planar tunnel metal/barrier/metal (MBM) structure with a 40-A-thick Al2O3 dielectric layer under the action of short-pulse voltage and hf electromagnetic emission is investigated. The optical response is greater than 10 -3 W of light per watt of hf signal in the measurement range of 500 to 1200 MHz. The MBM structure can be used as a fast-operating visualizer of hf signals.

A review of basic analytical results on coherent propagation of optical pulses through nondegenerate amplifying media is presented. Original numerical results concerning pulse coherent amplification by degenerate media and, in particular, by the amplifying medium of an iodine laser are described also. Furthermore, some analytical results on coherent effects in the pulsed mode of laser generation are given. We have pointed out that the stochastic mode of laser radiation is related also to the coherency of interaction of a laser field with matter.