Christos Flytzanis

Nonlinear optics in mesoscopic composite materials

We review the dominant processes that shape the optical nonlinearities of mesoscopic composite materials with particular emphasis on the photo-induced modifications of their spectral features that are related either to the electron or photon confinement in metal and semiconductor nanoparticles embedded in a transparent dielectric in low concentration. We also derive fluctuation–dissipation relations for the nonlinear regime in such systems. These modifications are related to the strong charge-photon coupling regime in confined space and can be exploited in different ways in applications and in particular as photonic nanoprobes with outstanding spatio-temporal resolution.

Spectral windowing with chirped magneto-optical Bragg gratings

We present a theory on a novel class of magneto-optical devices operated by means of magneto-optically induced refractive-index perturbations in chirped Bragg gratings. The predicted effect of the introduced perturbation is an opening of a narrow transmission window in the band-blocking transmission of the chirped grating. The narrow transmission window is tunable in wavelength, and relative transmission and the effects of multiple, spatially separated perturbations can also be superimposed, hence allowing for tunable, magneto-optically operated, multichannel add-drop multiplexors suitable for modularization in integrated optics.

OPTICAL AMPLITUDE AND PHASE EVOLUTION IN NONLINEAR MAGNETO-OPTICAL BRAGG GRATINGS

We present a theory on stratified nonlinear magneto-photonic crystals, with arbitrary spatial distribution of the refractive index and magneto-optical coefficients. The coupled mode theory is formulated for plane waves inside the crystal, and a perturbation series of integral solutions for the spectral response of the crystal is presented. Material issues and configurations are discussed, and the described theory is applied to the calculation of transmission spectra of binary magneto-photonic crystals.

Merging Nonlinear Acoustics and Optics : Light Driven Large Amplitude Short Acoustic Pulses and Breakdown in Dielectrics

We briefly review the basic schemes for optically driven sources of large amplitude acoustic pulses and large acoustic phonon populations down to the picosecond and submicron spatiotemporal scales. We sketch their applications in material diagnostics and devices operating in these time and space scales. We draw attention to the importance of the quantum acoustic phonon limit and noise.

Coherent Acoustic Phonon Amplification in a Strongly Coupled Semiconductor Superlattice under Intraminiband Transport

We report a new technique to amplify coherent acoustic phonons in a semiconductor superlattice under intraminiband transport. The interaction between drift electrons and copropagating acoustic phonons leads to an amplification of the sound amplitude by 200 %.

Ultrafast nonlinear terahertz studies of high-field charge transport in semiconductors

Nonlinear terahertz (THz) spectroscopy gives insight into high-field charge transport in semiconductors. Strong THz transients with field amplitudes of up to megavolts/cm serve as a driving field for free carriers and the resulting transport behavior is directly inferred from the field radiated by the moving charges. We study the transition from a ballistic to a drift-like transport regime of electrons in bulk GaAs. While electrons in the lowest conduction band of an n-type sample display ballistic transport, a transition to a drift-like behavior is found in an optically generated electron-hole plasma. Time-resolved measurements reveal the onset of friction on a time scale of a few picoseconds, mainly due to interactions of electrons with the hole distribution heated by the intense THz driving field. Experiments in which photoexcited electrons undergo intervalley scattering from the Γ to the L valley reveal characteristic changes of the transport behavior due to the picosecond backscattering to the Γ valley. The experimental results are in agreement with theoretical calculations of the time-dependent friction including both electron-hole scattering and local-field effects.

High field transport of photo-injected electrons in GaAs: Transition from ballistic to drift motion

Using visible/NIR pump and strong THz probe pulses, we observe the THz field emitted by accelerated photoelectrons in n-type GaAs. A transition from ballistic to drift motion is observed.

Directed photo-driven carrier, spin and phonon fluxes in polar layered heterostructures: photogalvanic effects

We review the photo-driven directed charge, spin and acoustic phonon transport in dielectrics and semiconductors, in bulk and hetero-structures, lacking spatial inversion symmetry. We express these photo-galvanic effects in terms of photo-induced driving forces bilinear in the coherent light field amplitude mediated through the spatial asymmetry of the medium. We discuss their interrelations with nonlinear optical analogues and also nonlinear optical time resolved techniques for their study. These issues are of certain relevance in optoelectronics and photonics and in the emerging fields of phononics and photo-spintronics as they introduce new unidirectional and nonreciprocal photonic functionalities. They are manifestations of photo-driven ratchet and pawl processes.

OPTICAL PARAMETRIC INTERACTIONS IN DISTRIBUTED MAGNETO-OPTICAL BRAGG GRATINGS

We analyze optical parametric interactions in nonlinear magneto-optical media simultaneously possessing a second-order nonlinearity and a spatial modulation of its linear optical properties. An analytic solution for the conversion efficiency of energy transfer from an optical pump to a signal wave is presented, and we discuss the possibility of tunability that is added to the parametric process.

Artificially Induced Perturbations in Chirped Magneto-Optical Bragg Gratings

We report on theoretical analysis of magneto-optically induced longitudinal perturbations in chirped magneto-optical Bragg gratings. The induced perturbations considered are of Lorentzian shape, with a spatial extent considerably larger than the spatial grating period but at least an order of magnitude less than the geometrical length of the grating. In the numerical simulation of the proposed device, we show on a high polarization state selectivity in the region of the perturbation, with resonance peaks of transmission for circularly polarized orthogonal components possessing a full width at half maximum as narrow as 0.18 nm, meanwhile being separated by 0.6 nm.