T.V. Murzina

Optical second-harmonic generation induced by a dc electric field at the Si–SiO 2 interface

For what is to our knowledge the first time, electric-field-induced optical second-harmonic generation (SHG) is studied at the Si-SiO(2) interface by the use of a metal-oxide-semiconductor (MOS) structure. The crystallographic anisotropy of this phenomenon is studied for MOS structures. Experimental results indicate that the MOS technique of dc electric-field application to the Si-SiO(2) interface can be effectively used for studying electroinduced effects on SHG.

Tunable ferroelectric photonic crystals based on porous silicon templates infiltrated by sodium nitrite

Ferroelectric photonic band-gap (PBG) structures are fabricated by the infiltration of sodium nitrite into the nanoporous silicon templates composed by the electrochemical etching of n-type silicon. Reversible spectral tuning of the PBG and of the microcavity mode up to 15nm is attained in the temperature interval from 50to165°C due to the temperature changes of the refractive index of sodium nitrite in nanoporous silicon matrix. Optical second-harmonic generation measurements prove the ferroelectric state of the composed nanocomposite PBG structures.

Magnetization-induced second- and third-harmonic generation in magnetic thin films and nanoparticles

The results of our recent experimental studies of magnetization-induced second- and third-order nonlinear optical effects in magnetic nanostructures are surveyed. Magnetization-induced variations of the intensity, the polarization state, and the relative phase of the second-harmonic wave are studied in magnetic nanogranular films, self-assembling films with garnet nanoparticles, thin magnetic metal films, and Langmuir-Blodgett films containing rare-earth ions. The nonlinear magneto-optical Kerr effect (NOMOKE) in second-harmonic generation (SHG) from thin magnetic and granular films is shown to exceed the linear magneto-optical Kerr effect by at least 1 order of magnitude. Magnetization-induced optical third-harmonic generation (THG) is observed in thin magnetic metal films and nanogranular films. The NOMOKE in THG from these magnetic nanostructures appears to be of the same order of magnitude as the second-order NOMOKE in SHG. The NOMOKE magnetic contrast in the THG intensity is up to ∼0.1 in Co_xAg(_1−x) nanogranular films. For the THG wave, the magnetization-induced rotation of polarization is up to 10° in thin Fe(110) films, and the relative phase shift is up to 70° in thin Co films. The studies of the magnetization-induced quadratic and cubic nonlinear-optical effects show the interconnection between the magnetic, structural, and magneto-optical properties of magnetic nanomaterials.

Magnetization-induced second- and third- harmonic generation in magnetophotonic crystals

The results of our recent studies of magnetization-induced nonlinear-optical second- and third-order effects in magnetophotonic crystals and magnetophotonic microcavities are surveyed. Magnetophotonic crystals (MPCs) are fabricated from a stack of four repetitions of lambda/4-thick layers of Bi-substituted yttrium iron garnet (Bi:YIG) and lambda/4-thick SiO2 layers. Magnetophotonic microcavities (MMCs) are formed from two dielectric (nonmagnetic) Bragg reflectors and ferromagnetic cavity spacers that are lambda/2-thick Bi:YIG layers. The nonlinear magneto-optical Kerr effect (NOMOKE), both in magnetization-induced second-harmonic generation (MSHG) and magnetization-induced third-harmonic generation (MTHG), is observed in MMCs at wavelengths of the resonant microcavity modes. Magnetization-induced variations of MSHG and MTHG intensities, as well as magnetization-induced shift of phase and rotation of polarization of second and third-harmonic waves, are observed in proper - transversal, longitudinal, or polar - NOMOKE configurations. Manyfold enhancement of the absolute values of both the MSHG and MTHG intensities are attributed to the localization of the resonant fundamental radiation in Bi:YIG microcavity spacers. The NOMOKE in MSHG intensity is observed in MPCs in the spectral range of photonic bandgap (PBG) edges. The MSHG intensity reveals enhancement by a factor of more than 10^2 if the fundamental wavelength is tuned in the vicinity of the PBG edge. This enhancement is attributed to the fulfillment of the phase-matching conditions for MSHG effect in layered structures with periodic modulation of both optical (magneto-optical) and nonlinear optical parameters.

Hybrid microspheres for nonlinear Kerr switching devices

Electronic Kerr effect in a polyfluorene derivative is used to reversibly switch near infrared probe beam resonantly coupled to a hybrid polymer-silica microspherical resonator. NIR pumping at 780 nm in pulsed laser regime is used for non-linear switching of the WGM resonances that shift as much as 2 GHz for 50 mW of average pump power, compared to a shift of 250 MHz for the same average pump power at CW regime. The absence of temporal drift and the magnitude of this shift confirm the Kerr nature of the switching, ruling out thermooptical effects.

Magnetic field induced effects in optical second harmonic generation from iron-garnet films

Abstract The magnetic field induced effects in the second harmonic generation (SHG) from epitaxially grown iron-garnet films have been studied. The magnetic field induced variations in the azimuthal angular dependences and the polarization diagrams of the SHG intensity are shown to be due to the linear Faraday effect. Enhancements in the SHG intensity were detected for (Bi,Gd,Fu) 3 (Fe,Ga) 5 O 12 iron-garnet films grown on (Gd,Ca) 3 (Mg,Zr,Ga) 5 O 12 single-crystal substrates with various orientations. This dependence of the SHG intensity on the magnetic field may be caused by magnetostriction effects.

The photoinduced anisotropy of second harmonic generation in monolayered Langmuir—Blodgett films

Abstract Photoinduced anisotropy of non-linear optical properties of Langmuir-Blodgett films of 4-nitro-4′-octadecilazobenzene has been studied for the first time by means of second harmonic generation. It was shown that the anisotropy of second order susceptibility of the films could be controlled by illuminating them by polarized visible CW radiation. The primary non-linear susceptibility corresponded to the direction perpendicular to the polarization vector of the CW radiation. These transformations of the films were reversible and could be repeated many times. Possible mechanisms of such a reconstruction of the films are discussed.

Optical study of polymer infiltration into porous Si-based structures

This work describes the infiltration of a polymeric solution into porous Si structures towards the fabrication of tunable photonic crystals (PC) and microcavities for photonics applications. The tunability is achieved by infiltrating the porous silicon based PCs by active organic materials, such as an emissive and nonlinear polymer called 2-methoxy-5-(2- ethylhexyloxy)-p-phenylenevinylene (namely MEH-PPV). This preliminary work shows the infiltration of this polymeric solution into PC based on macroporous Si structure as well as in microcavities based on multiple layers of microporous Si. The solidification of the polymer was obtained by the evaporation of the solvent. Various techniques of infiltration were studied to obtain an optimized filling of the pores. The infiltration was then characterized using photoluminescence measurements. Finally, we will report on the study of third harmonic generation (THG) in samples of porous silicon microcavity infiltrated with MEHPPV. The k-domain THG spectroscopy was applied and an increase of the THG intensity up to an order of magnitude was achieved for the filled microcavity.

DC-electric-field-induced optical second harmonic generation at the smooth metal-electrolyte interface

The reflected second harmonic (SH) intensity is established to be a quadratic function of voltage applied to the smooth silver-electrolyte interface in a wide range of angles of incidence of the fundamental radiation. The nonlinear reduction problem is solved to recapture the voltage dependence of Rudnick-Sterns parameter a(ϕ) that turns out to be linear in the range from −0.5 to −1.2 V (versus saturated AgAgCl electrode). In this range, the electro-induced nonlinearity of conduction electrons is the predominant mechanism behind the electric-field-induced SH. The deviations from linear dependence of a(ϕ) are associated with the specific adsorption of anions.

Second Harmonic Generation and Atomic-Force Microscopy Studies of Porous Silicon

Structural properties of porous silicon were studied with atomic‐force microscopy (AFM) and optical second harmonic generation (SHG). Depending on etching conditions, the SHG response was observed to be either anisotropic, showing C2v symmetry, or isotropic. This correlated with AFM observations of quasi ordered structures in the first case. The Si etching process was studied by in situ SHG measurements.