L. A. Kulakova

Fine spectroscopy of the dynamics of heterolaser radiation in the presence of an ultrasonic strain

This paper reports on the experimental data on the dynamics (in real time) of the emission spectra of InGaAsP/InP heterolasers, including those in the presence of an alternating strain. A computational model is proposed for the fine dynamic spectral analysis. A comparative investigation of the methods used for the fine analysis of the emission spectra of heterolasers is performed, and the advantages of the dynamic method for studying the ultrasonic action on the emission spectra of laser heterostructures are demonstrated.

Kinetics of the phase transition in crystals PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–xPbTiO3

The time dependences of the optical transmission, velocity of sound, and elastic constants at room temperature in a number of the [001]-oriented PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–xPbTiO3 single crystals with the compositions lying both far from the morphotropic phase boundary and in its vicinity have been investigated. The analysis of the data obtained has been carried out. It has been shown that, in all the studied crystals, phase transitions induced by an electric field occur in two stages: the first stage is an incubation period associated with a small increase in the polarization of a part of the sample being in the glass phase, and the second phase (after the incubation period τ) is a rapid increase in the polarization and the formation of a long-range order. It has been found that the time τ depends on how close is the temperature of measurements to the Vogel–Fulcher temperature Tf. The closer is the temperature of measurements to the Vogel–Fulcher temperature Tf, the weaker is the electric field required to be applied to the sample in order to induce a ferroelectric phase. It has been demonstrated that the phase state of the studied crystals is unstable, which manifests itself in a strong dependence of the incubation period τ on the time between the annealing of the sample and the beginning of the measurements. The stability of the phase state depends on the PbTiO3 concentration: an increase in the concentration leads to a significant increase in the stability.

Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In1/2Nb1/2)O3-35PbMg1/3Nb2/3O3-32PbTiO3 existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.

Electric field-induced dynamics of structural ordering in ternary PbIn 1/2 Nb 1/2 O 3 –PbMg 1/3 Nb 2/3 O 3– x PbTiO 3 systems

The electric field-induced dynamics of the phase transition to a ferroelectric phase in PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–xPbTiO3 (x = 25 and 32%) crystals have been studied in different geometries of applying an external electric field E|| [001] and E || [011]. The optical transmission, the sound velocity, and the sound damping have been measured simultaneously at room temperature. It was found that the change in the elastic properties follows the change in the optical transmission, which is related to different polar region sizes and relaxation times, to which light and sound are responsive. It was found that, in the field range 0–2 kV/cm at E|| [001], both the crystals demonstrate only a partial polarization as a result of the phase transition, while the phase transition in the PT32 crystal at E|| [011] is finished by almost complete polarization of the sample in the same field range.

Acoustical investigations of a La0.75Sr0.25MnO3 single crystal

The acoustical, resistive, and magnetic properties of a La0.75Sr0.25MnO3 lanthanum manganite single crystal are investigated in the temperature range involving the second-order magnetic phase transition. The acoustical measurements are performed by the pulse-echo method in the frequency range 14–90 MHz. It is found that, as the temperature decreases, the velocity of a longitudinal acoustic wave propagating along the [111] axis in the single crystal drastically increases at temperatures below the critical point of the magnetic phase transition. No dispersion of the acoustic velocity is revealed. A sharp increase in the acoustic velocity is accompanied by the appearance of an acoustical absorption peak. The observed effects are discussed with due regard for the interaction of acoustic waves with the magnetic moments of the manganese ions.

Transformation of the physical properties of PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–PbTiO3 crystals in an electric field

The influence of the composition and different modes of applying a direct-current (dc) electric field (0 < E < 4 kV/cm) on the behavior of the temperature dependences of the dielectric permittivity, optical transmission, as well as the velocity and attenuation of sound, has been investigated in the [001]-oriented PbIn1/2Nb1/2O3–PbMg1/3Nb2/3O3–PbTiO3 single crystals located both far from the morphotropic phase boundary and in its vicinity. It has been found that, in the phase transition region in a narrow field range for any mode of applying an electric field, all the crystals under investigation are characterized by abrupt changes in their physical properties. It has been shown that the phase transition rate and the attenuation of sound are different in the crystals located at different distances from the morphotropic phase boundary. The E–T phase diagrams have been constructed for different modes of applying an electric field. It has been demonstrated that the phase diagrams constructed for the same crystal but different modes of applying an electric field differ from each other. Possible reasons for the observed phenomena have been discussed.

Effects of induced birefringence in nanoscale heterostructures

The influence of a complex of elastic strains caused by technological stresses and external shear strains on the optical properties of cubic crystals has been analyzed. Data on the changes in optical symmetry of such crystals have been obtained. The changes in polarization characteristics of the radiation during propagation in both strained crystal and shear-strained nanoscale heterostructures have been studied. The effects of the acoustoelectronic and photoelastic deformation mechanisms on the changes in polarization properties of the radiation of nanoscale heterostructures have been compared.

Acoustoelectronic Interaction in InGaAsP∕InP Laser Heterostructures

The dynamics of change in the spectral characteristics of the emission from a laser heterostructure due to an alternating strain induced by a surface acoustic wave is investigated. The spectral distributions of the laser radiation intensities are analyzed with the aim of elucidating the mechanisms responsible for the interactions occurring in the laser heterostructure. A model is proposed for describing the experimental data, and their theoretical analysis is performed. It is demonstrated that the acoustoelectronic interaction is dominant under the action of surface waves. The deviation of the observed frequency modulation of radiation is determined from a comparison of the theoretical calculations with experimental data.

Anomalies of elastic properties of layered materials

Acoustic investigations of layered crystals KY(MoO4)2 and glassy alloys Si20Te80 (with inclusions of nanocrystallites) are performed with the purpose of elucidating the character of binding forces in layered materials. The absorption and velocity of sound, as well as the spatial evolution of the spectrum of acoustic fluxes in various directions in wide ranges of temperatures (90–300 K), frequencies (14–1800 MHz), and intensities (0.04–100 W/cm2) of sound, are measured. Acoustooptical and pulse-echo methods were used for the measurements. A theoretical analysis of the data obtained has revealed anomalously large values of the nonlinear elastic coefficients and anharmonicity constants of longitudinal phonon modes that are determined by the anharmonicity of binding forces across the layers and at boundaries with nanocrystallites. It is shown that the anisotropy of the mechanical strength of layered crystals is to a large extent determined by the anharmonicity of binding forces.

Polarization effects in quantum-well In 28 Ga 72 As/GaAs heterolasers

The effect of externally introduced variable strains on the polarization properties of quantum-well In28Ga72As/GaAs laser radiation at room temperature is studied experimentally and theoretically. An analysis of the polarization effects at various values of the excess of the working current over the threshold is performed. Data on the energy for the splitting of the levels of light and heavy holes in the quantum well of the structure under consideration are obtained. It is experimentally proven that the effectiveness of the action of a variable strain on the polarization twist substantially increases with increasing quantum well width.