Olga Sergaeva

Dynamically reconfigurable metal-semiconductor Yagi-Uda nanoantenna

We theoretically investigate the properties of a tunable Yagi-Uda nanoantenna composed of metal-dielectric (Ag-Ge) core-shell nanoparticles. We show that, due to the combination of two types of resonances in each nanoparticle, such hybrid Yagi-Uda nanoantenna can operate in two different regimes. Besides the conventional nonresonant operation regime at low frequencies, characterized by highly directive emission in the forward direction, there is another one at higher frequencies caused by a hybrid magneto-electric response of the core-shell nanoparticles. This regime is based on the excitation of the van Hove singularity, and emission in this regime is accompanied by high values of directivity and Purcell factor within the same narrow frequency range. Our analysis reveals the possibility of flexible dynamical tuning of the hybrid nanoantenna emission pattern via electron-hole plasma excitation by 100 fs pump pulse with relatively low peak intensities similar to 200 MWcm(-2).

Ultrafast excitation of conduction-band electrons by high-intensity ultrashort laser pulses in band-gap solids: Vinogradov equation versus Drude model

Heating of conduction-band electrons is one of the major processes of energy absorption and transfer in high-intensity ultrafast laser–solid interactions. It is frequently simulated by assuming a high rate of electron-particle collisions. We explore the approximation of low-rate electron–phonon collisions based on the Vinogradov equation for the intraband absorption rate by conduction-band electrons performing laser-driven oscillations. Band-structure modification by the ponderomotive energy of the ultrafast oscillations is taken into account. The Vinogradov equation combined with the Keldysh formula for the interband transition rate delivers a highly nonequilibrium energy distribution of the conduction electrons. Reported results suggest a substantial revision of the traditional models of ultrafast free-carrier heating by intense laser pulses.

Ultrafast mechanism of energy-band modification of wide-band-gap crystals by pondermotive potential of Gaussian ultrashort laser pulse

Modification of energ4y bands of wide-band-gap crystals by ultrashort (10⁻¹⁴-10⁻¹⁵ seconds) laser pulse is theoretically studied. Formation of transient indirect-gap structure from original direct-gap one is predicted and characterized for a Gaussian pulse envelope.

Simulations of ultrafast laser-induced excitation and heating of electron sub-system of semiconductors with the Vinogradov equation and multi-band Keldysh formula

High-intensity laser interactions with band-gap solids are frequently simulated with the Keldysh photoionization-rate formula and the Drude model to describe light absorption and related heating of conduction-band electrons. That approach suffers from several internal contradictions. We fix some of them by combining the Vinogradov equation for energy absorption with multi-band version of the Keldysh equation for the rate of photoionization.

Core-shell Yagi-Uda nanoantenna for highly efficient and directive emission

We study radiation from hybrid Yagi-Uda nanoantennas composed of metal-dielectric core-shell nanoparticles. We show that due to the presence of two types of resonances in each particle at close frequencies the hybrid Yagi-Uda nanoantenna can operate in two different regimes. In the first regime at low frequencies it operates similarly to plasmonic and all-dielectric Yagi-Uda nanoantennas, and it is characterized with highly directive emission in a forward direction. In the second regime at higher frequencies the hybrid nanoantenna can emit with a high directivity in backward direction due to the presence of the hybrid dispersion branch with negative group velocity. Moreover by choosing the appropriate nanoantenna parameters one can achieve the operation regime when due to excitation of dark magnetic dipole modes in nanoantenna high values of directivity and Purcell factor are realized simultaneouslly in extremely narrow frequency range.