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Register a new userPolarization conversion spectroscopy of hybrid modes
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Enhanced polarization conversion in reflection for the Otto and Kretschmann configurations is introduced as a new method for hybrid-mode spectroscopy. Polarization conversion in reflection appears when hybrid-modes are excited in a guiding structure composed of at least one anisotropic media. In contrast to a dark dip, in this case modes are associated to a peak in the converted reflectance spectrum, increasing the detection sensitivity and avoiding confusion with reflection dips associated with other processes as can be transmission.
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Using time-resolved $1s$-$2p$ excitonic Lyman spectroscopy, we study the orthoexciton-to-paraexcitons transfer, following the creation of a high density population of ultracold $1s$ orthoexcitons by resonant two-photon excitation with femtosecond pulses. An observed fast exciton-density dependent conversion rate is attributed to spin exchange between pairs of orthoexcitons. Implication of these results on the feasibility of BEC of paraexcitons in Cu$_2$O is discussed.
Optical control of electronic spins is the basis for ultrafast spintronics: circularly polarized light in combination with spin-orbit coupling of the electronic states allows for spin manipulation in condensed matter. However, the conventional approach is limited to spin orientation along one particular orientation that is dictated by the direction of photon propagation. Plasmonics opens new capabilities, allowing one to tailor the light polarization at the nanoscale. Here, we demonstrate ultrafast optical excitation of electron spin on femtosecond time scales via plasmon to exciton spin conversion. By time-resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantum well structure covered with a metallic grating, we unambiguously determine the orientation of the photoexcited electron spins which is locked to the propagation direction of surface plasmon-polaritons. Using the spin of the incident photons as additional degree of freedom, one can orient the photoexcited electron spin at will in a two-dimensional plane.
In nanostructure electronic devices, it is well-known that the optical lattice waves in the constituent semiconductor crystals have to obey both mechanical and electrical boundary conditions at an interface. The theory of hybrid optical modes, established for cubic crystals, is here applied to hexagonal crystals. In general, the hybrid is a linear combination of a longitudinally-polarized (LO) mode, an interface mode (IF), and an interface TO mode. It is noted that the dielectric and elastic anisotropy of these crystals add significant complications to the assessment of the electro-phonon interaction. We point out that, where extreme accuracy is not needed, a cubic approximation is available. The crucial role of lattice dispersion is emphasised. In the extreme long-wavelength limit, where lattice dispersion is unimportant, the polar optical hybrid consists of an LO component plus an IF component only. In his case no fields are induced in the barrier, and there are no remote-phonon effects.
We have obtained spectra of second-harmonic generation, third harmonic generation, and four-wave mixing from a fishnet metamaterial around its magnetic resonance. The resonant behaviors are distinctly different from those for ordinary materials. They result from the fact that the resonance is plasmonic, and its enhancement appears through the local field in the nanostructure.
We demonstrate the modification of coherent zone-folded longitudinal acoustic phonons (ZFLAPs) oscillations in InGaN/GaN multiple quantum wells by the inclusion of metal nanoparticles (Au and Ag) via self-assembled inverted hexagonal pits. Blueshift and redshift have been observed in photoluminescence spectra due to the effect of electrostatic charge of metal nanoparticles (NPs). A change in periodicity of ZFLAPs oscillations were demonstrated due to the metal NPs inserted in the material system.
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