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1.
Determination of the magnitude and distribution of the initial stresses in glass-reinforced plastics
Photoelastic stress analysis is used to demonstrate the effect of coupling agents on the residual microstresses, i.e., the stresses that develop at near the glass-resin interface during the curing of polyester and epoxy glass-reinforced plastics and, as a rule, remain throughout the life of the product. Coupling agents of different chemical composition applied to the surface of the glass fibers have different effects on the components of the state of stress and thus can act as a powerful regulating factor. 相似文献
2.
3.
Nonlinear absorption of 30-ps light pulses with λ = 560 nm in AgBr nanocrystals is experimentally studied in the range of intensities 108–1010 W/cm2. The results of a theoretical analysis show that the absorption is related to direct interband n-photon transitions. With increasing light intensity j, the number n increases and the region of the k-space changes for the transitions predominantly contributing to the absorption. It is shown that, due to specific features of the AgBr electronic band structure, the probabilities of two-photon transitions for the light at λ = 560 nm are anomalously low, while those of four-photon transitions are anomalously high. In addition, the increase in the two-photon transition rate with increasing intensity is blocked at j ? 108 W/cm2 due to the resonant optical Stark effect and due to a gap arising in the band spectrum, rearranged because of the interaction with light. 相似文献
4.
E. Yu. Perlin 《Optics and Spectroscopy》2000,88(6):898-903
The amplitude and dispersion of the cubic susceptibility-tensor components χ ijkl (3) (?Ω; Ω, ω, ?ω) and of their combinations responsible for the Kerr and Faraday optical effects, as well as for the self-rotation of the polarization ellipse, are calculated within a simple model of a material with semiconducting spherical quantum dots without the inclusion of the excitonic effects and of processes of higher orders in field. It is shown that the susceptibilities increase smoothly in amplitude below the two-photon absorption threshold while remaining negative. Above the threshold, the susceptibilities exhibit sharp maxima associated with two-photon resonances. The regions with positive and negative real parts of the χ(3) tensor components alternate. The magnitude of the induced linear or circular birefringence obtained suggest the possibility of using the nonlinear optical polarization effects in these materials to control light with short, high-intensity light pulses. 相似文献
5.
We show that an intense pump pulse, detuned far from the Bragg resonance of a nonlinear periodic structure, can excite a gap soliton at a wavelength within the band gap that corresponds to the Raman shift of the medium. This Raman gap soliton is a stable, long-lived, quasistationary excitation that exists within the grating even after the pump pulse has passed. We find both stationary solitons as well as slow Raman gap solitons with velocities as low as 1% of the speed of light. The predicted phenomena should be observable in fiber Bragg gratings and other nonlinear photonic band gap structures. 相似文献
6.
T. Suski E. Litwin-Staszewska P. Perlin P. Wisniewski H. Teisseyre I. Grzegory M. Bockowski S. Porowski K. Saarinen J. Nissil 《Journal of Crystal Growth》2001,230(3-4):368-371
Highly resistive GaN : Be was obtained by means of synthesis of Ga+Be with atomic nitrogen under high nitrogen pressure. Activation energy of resistivity is about 1.5 eV. This material exhibits features very different from those observed in highly resistive bulk GaN : Mg. Up to 300 K strong yellow band dominates photoluminescence spectrum in resistive GaN : Be crystals. Positron annihilation studies point to the presence of gallium vacancies, VGa. In highly resistive GaN:Mg neither yellow band with considerable intensity, nor detectable concentration of VGa was found. We also discuss the puzzling findings in highly resistive bulk GaN : Be of morphological features typical for highly conducting bulk n-GaN material. 相似文献
7.
Tatiana A. Vovk Semyon S. Rudyi Andrei V. Ivanov Evgeniy Y. Perlin Yuri V. Rozhdestvensky 《Physics letters. A》2019,383(9):923-928
One of the most interesting problems of modern physics is the realization of nanoparticles in macroscopic quantum states, in which they behave as a quantum objects. These states can only be implemented at ultra-low translational temperatures that have not been achieved so far. Here we develop a novel method for optical cooling of CaF2:Yb3+ nanocrystals, which is based on the coherent population transfer induced in the impurity ions by ultraviolet Raman pulses. A doped nanocrystal localized in a radio-frequency trap is cooled due to the photon recoil from the pulses of varied intensity. The proposed method allows to obtain nanocrystals with translational temperatures of the order of 10?9 K, which indicates that the nanocrystal approaches a macroscopic quantum state. 相似文献
8.
The probabilities of multiphoton transitions between the valence and conduction bands at two-photon resonance on the adjacent transition between two conduction bands are calculated within the three-band model of a crystal. It is shown that, due to the effects of transformation of electronic band spectrum in the field of a strong light wave, the dependence of the multiphoton generation rate of electron-hole pairs on the light intensity j contains ranges where a small change in j leads to an increase in the generation rate of electron-hole pairs by several orders of magnitude, which may increase the number of nonequilibrium carriers to the level sufficient for initiating destruction of the material. 相似文献
9.
A new mechanism for generating nonequilibrium electron-hole pairs in transparent wide-gap crystals under high-power picosecond
light pulses of prebreakdown intensity is considered. The kinetics of free carrier generation is investigated by the numerical
solution of the system of balance equations for particle concentrations within the multiband model of electron energy spectrum
of the crystal. It is shown that in the intensity range of 1010–1012 W/cm2 the proposed way of nonequilibrium carrier generation is more effective in the case of picosecond pulses than the conventional
multiphoton absorption. It is shown that the nonequilibrium carrier generation considered here may initiate a multiphoton
avalanche. 相似文献
10.
The dependences of the energy that is absorbed in a crystal exposed to the action of a femtosecond light pulse on the radiation intensity at a fixed pulse duration and on the pulse duration at a fixed pulse energy have been determined under the conditions of a two-photon–one-photon double resonance on interband transitions in the crystal. 相似文献