Tunable local polariton modes in semiconductors

We study the local states within the polariton bandgap that arise due to deep defect centers with strong electron-phonon coupling. Electron transitions involving deep levels may result in alteration of local elastic constants. In this case, substantial reversible transformations of the impurity polariton density of states occur, which include the appearance/disappearance of the polariton impurity band, its shift and/or the modification of its shape. These changes can be induced by thermo- and photo-excitation of the localized electron states or by trapping of injected charge carriers. We develop a simple model, which is applied to the $O_P$ center in $GaP$. Further possible experimental realizations of the effect are discussed.Comment: 7 pages, 3 figure

Emission Spectrum of a Dipole in a Semi-infinite Periodic Dielectric Structure: Effect of the Boundary

The emission spectrum of a dipole embedded in a semi-infinite photonic crystal is calculated. For simplicity we study the case in which the dielectric function is sinusoidally modulated only along the direction perpendicular to the boundary surface plane. In addition to oscillations of the emission rate with the distance of the dipole from the interface we also observed that the shape of the emission spectrum srongly depends on the \em initial \em phase of the dielectric modulation. When the direction of light propagation inside the periodic structure is not normal to the boundary surface plane we observed aditional singularities in the emission spectrum, which arise due to different angle-dependence of the Bragg stop-band for $TE$ and $TM$ polarizations.Comment: 14 pages, 6 figures, to appear in Phys Rev

Microsecond Z-pinch as ultrasoft X-ray radiation source

The spectral characteristics of plasma radiation of a gas Z-pinch with a rise time of 1 ${\rm \mu}$s and a current amplitude of 250 kA have been measured. The measurements were performed in the range of X-ray energy quanta from 30eV to 600 eV. A spectrograph with a transmission grating and a polychromator on the basis of multilayer X-ray mirrors served as the diagnostic devices. Absolutely calibrated semiconducting detectors AXUV-5 were used as radiation detectors in the polychromator. The full pinch radiation loss was measured with a thermocouple calorimeter. The radiation of He-, Li- and Be- like ions has been shown to dominate at the stage of maximum compression of the nitrogen Z-pinch. The results of the spectral measurements were employed for the absolute calibration of various X-ray detectors

Theory of Gap Solitons in Short Period Gratings

Series "Lecture Notes in Physics