Andrey A. Fedyanin

Enhanced Third-Harmonic Generation in Silicon Nanoparticles Driven by Magnetic Response

We observe enhanced third-harmonic generation from silicon nanodisks exhibiting both electric and magnetic dipolar resonances. Experimental characterization of the nonlinear optical response through third-harmonic microscopy and spectroscopy reveals that the third-harmonic generation is significantly enhanced in the vicinity of the magnetic dipole resonances. The field localization at the magnetic resonance results in two orders of magnitude enhancement of the harmonic intensity with respect to unstructured bulk silicon with the conversion efficiency limited only by the two-photon absorption in the substrate.

Ultrafast All-Optical Switching with Magnetic Resonances in Nonlinear Dielectric Nanostructures

We demonstrate experimentally ultrafast all-optical switching in subwavelength nonlinear dielectric nanostructures exhibiting localized magnetic Mie resonances. We employ amorphous silicon nanodisks to achieve strong self-modulation of femtosecond pulses with a depth of 60% at picojoule-per-disk pump energies. In the pump-probe measurements, we reveal that switching in the nanodisks can be governed by pulse-limited 65 fs-long two-photon absorption being enhanced by a factor of 80 with respect to the unstructured silicon film. We also show that undesirable free-carrier effects can be suppressed by a proper spectral positioning of the magnetic resonance, making such a structure the fastest all-optical switch operating at the nanoscale.

Anomalous Faraday effect of a system with extraordinary optical transmittance.

It is shown theoretically that the Faraday rotation becomes anomalously large and exhibits extraordinary behavior near the frequencies of the extraordinary optical transmittance through optically thick perforated metal film with holes filled with a magneto-optically active material. This phenomenon is explained as result of strong confinement of the evanescent electromagnetic field within magnetic material, which occurs due to excitation of the coupled plasmon-polaritons on the opposite surfaces of the film.

Surface-plasmon-induced enhancement of magneto-optical Kerr effect in all-nickel subwavelength nanogratings

Enhancement of transversal magneto-optical Kerr effect (TKE) is controlled experimentally in magnetoplasmonic subwavelength nanogratings made of nickel films by resonant excitation of surface plasmon-polaritons (SPPs). Almost one order of magnitude increase of the TKE value is observed in the spectral range of Wood’s anomaly corresponding to the fulfillment of the phase-matching conditions for SPP excitation.

Multifold Enhancement of Third-Harmonic Generation in Dielectric Nanoparticles Driven by Magnetic Fano Resonances

Strong Mie-type magnetic dipole resonances in all-dielectric nanostructures provide novel opportunities for enhancing nonlinear effects at the nanoscale due to the intense electric and magnetic fields trapped within the individual nanoparticles. Here we study third-harmonic generation from quadrumers of silicon nanodisks supporting high-quality collective modes associated with the magnetic Fano resonance. We observe nontrivial wavelength and angular dependencies of the generated harmonic signal featuring a multifold enhancement of the nonlinear response in oligomeric systems.

Giant microcavity enhancement of second-harmonic generation in all-silicon photonic crystals

Second-harmonic generation (SHG) spectra of single and coupled porous silicon-based photonic crystal microcavities are studied in both frequency and wave vector domains. For the fundamental field resonant to the microcavity mode the second-harmonic intensity is enhanced by 102 times in comparison with that outside the photonic band gap. SHG spectroscopy in identical microcavities coupled through the intermediate Bragg reflector reveals two SHG peaks if the fundamental field is in resonance with the splitted mode of coupled microcavities. The spatial confinement of the resonant fundamental radiation is directly probed at the microcavity cleavage by scanning near-field optical microscopy.

Observation of hybrid state of Tamm and surface plasmon-polaritons in one-dimensional photonic crystals

Experimental observation of hybrid mode of Tamm plasmon-polariton and surface plasmon-polariton is reported. The hybrid state is excited in one-dimensional photonic crystal terminated by semitransparent metal film under conditions of total internal reflection for transverse-magnetic-polarized light. Coupling between Tamm and surface plasmon-polaritons leads to repulsion of their dispersion curves controlled by metal film thickness.

Fluorescence emission enhanced by surface electromagnetic waves on one-dimensional photonic crystals

An appreciable increase in the fluorescence emission of an organic chromofore is obtained by exploiting the local field enhancement at the surface of one-dimensional photonic crystals after excitation of surface electromagnetic waves (SEW). Using a properly designed photonic crystal consisting of alternating a-Si1−xNx:H layers with different nitrogen content, efficient emission of R6G dye spun on the surface of the photonic crystal is detected and the intensity spatial distribution of the SEW is visualized by means of far-field fluorescence microscopy. Our results demonstrate potential applications in enhanced fluorescence microscopy with an increased sensitivity and spectral selectivity.

dc-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy of Si(001)-SiO2 interfaces

The mechanism of dc-electric-field-induced second-harmonic ~EFISH! generation at weakly nonlinear buried Si(001)-SiO2 interfaces is studied experimentally in planar Si(001)-SiO 2-Cr MOS structures by optical second-harmonic generation spectroscopy with a tunable Ti:sapphire femtosecond laser. The spectral dependence of the EFISH contribution near the direct two-photon E1 transition of silicon is extracted. A systematic phenomenological model of the EFISH phenomenon, including a detailed description of the space-charge region ~SCR! at the semiconductor-dielectric interface in accumulation, depletion, and inversion regimes, has been developed. The influence of surface quantization effects, interface states, charge traps in the oxide layer, doping concentration, and oxide thickness on nonlocal screening of the dc-electric field and on breaking of inversion symmetry in the SCR is considered. The model describes EFISH generation in the SCR using a Green’s-function formalism which takes into account all retardation and absorption effects of the fundamental and second-harmonic ~SH! waves, and multiple reflection interference in the SiO 2 layer. The optical interference between field-dependent and -independent contributions to the SH field is considered as aninternal homodyne amplifier of the EFISH effects. Good agreement between the phenomenological model and our EFISH spectroscopic results is demonstrated. Finally, low-frequency electromodulated EFISH is demonstrated as a useful differential spectroscopic technique for studies of the Si-SiO 2 interface in silicon-based metaloxide-semiconductor structures. @S0163-1829~99!01836-6#

Second-harmonic generation in metal and semiconductor low-dimensional structures

Abstract In this article previous and recent results of our nonlinear optical studies of low-dimensional structures are surveyed. Size effect in the optical second-harmonic generation (SHG) from Ag nanocrystals in island films and CdSe quantum dots in glass matrices as well as thermo- and DC-electric-field-induced effects in SHG from SiSiO2 multiple quantum wells (MQWs) on Si substrate are studied experimentally and theoretically. Essential (by several orders of magnitude) enhancement of quadratic optical response upon decrease in the particle size is observed for both Ag nanocrystals and CdSe quantum dots. Regular oscillations in the second-harmonic intensity measured as functions of temperature and applied DC electric field are observed for MQWs. It is shown that the size effect for metal nanocrystals can result from the fluctuations of the particle size breaking the local inversion symmetry. Another mechanism studied (based on concepts of dynamic chaos) describes the observed size effects for both metal and semiconductor particles. The dependence of the second-harmonic intensity on the SiO2 layer thickness in MQWs is described with taking into account the retardation of the second-harmonic radiation in MQWs, whereas the thermoinduced effect is interpreted as resulting from the optical interference in the MQWs substrate having thickness dependent on temperature (due to the thermal expansion). A possible approach to explaining the observed electroinduced effect in MQWs is also discussed.