Yuri Svirko

Layered chiral metallic microstructures with inductive coupling

A bilayered quasiplanar metallic microstructure, comprising an ensemble of fully metallic “molecules” with inductive coupling between two parts of the molecule, is predicted to show strong optical rotatory power.

Optical activity in subwavelength-period arrays of chiral metallic particles

We report on a chirality-induced polarization effect in a planar subwavelength metallic nanograting. We demonstrate that the grating rotates the polarization at normal incidence. Because of the fourfold rotation symmetry, the effect does not depend on the incident beam polarization, but resembles optical activity in isotropic media. We use rigorous diffraction theory to show that polarization effects in the zeroth diffraction order take place in the presence of waveguide resonances with subwavelength-period arrays of chiral metallic particles.

Numerical phase correction method for terahertz time-domain reflection spectroscopy

We propose a numerical method for the misplacement phase error correction in terahertz time-domain reflection spectroscopy (THz-TDRS). The developed algorithm is based on the maximum entropy principle and can be readily implemented into data processing, allowing one to reveal material parameters of the opaque materials from the THz reflection measurements. The method resolves the phase retrieval problem in the THz-TDRS and dramatically simplifies the experimental procedure.

Broadband Light-Induced Absorbance Change in Multilayer Graphene

We report the ultrafast light-induced absorbance change in CVD-grown multilayer graphene. Using femtosecond pump-probe measurements in 1100-1800 nm spectral range, we revealed broadband absorbance change when the probe photon energy was higher than that of the pump photon. The observed phenomenon is interpreted in terms of the Auger recombination and impact ionization playing a significant role in the dynamics of photoexcited carriers in graphene.

Effect of surface plasmon resonance on the optical activity of chiral metal nanogratings.

We examine the mechanism responsible for the optical activity of a two-dimensional array of gold nanostructures with no mirror symmetry on a dielectric substrate. Measurements with different incident angles, polarizations and sample orientations allow us to reveal that observed polarization effect is enhanced by surface plasmon resonance. By performing numerical simulation with rigorous diffraction theory we also show that the grating chirality can be described in terms of the non-coplanarity of the electric field vectors at the front (air-metal) and back (substrate-metal) sides of the grating layer.

Multipolar analysis of second-harmonic radiation from gold nanoparticles

We present a multipolar tensor analysis of second-harmonic radiation from arrays of noncentrosymmetric L-shaped gold nanoparticles. Our approach is based on the fundamental differences in the radiative properties of electric dipoles and higher multipoles, which give rise to differences in the nonlinear response tensors for the reflected and transmitted second-harmonic signals. The results are analyzed by dividing the tensors into symmetric (dipolar) and antisymmetric (higher multipolar) parts between the two directions. The nonlinear response is found to be dominated by a tensor component, not resolved earlier [Phys. Rev. Lett. 98, 167403 (2007)], which is associated with chiral symmetry breaking of the sample and which also contains a strong multipolar contribution. The results are explained by a phenomenological model where asymmetrically-distributed defects on opposite sides of the particles give rise to dipolar and quadrupolar second-harmonic emission.

Photosensitivity control of an isotropic medium through polarization of light pulses with tilted intensity front

We present the first experimental evidence of anisotropic photosensitivity of an isotropic homogeneous medium under uniform illumination. Our experiments reveal fundamentally new type of light induced anisotropy originated from the hidden asymmetry of pulsed light beam with a finite tilt of intensity front. We anticipate that the observed phenomenon, which enables employing mutual orientation of a light polarization plane and pulse front tilt to control interaction of matter with ultrashort light pulses, will open new opportunities in material processing.

Observation of extraordinary optical activity in planar chiral photonic crystals.

Control of light polarization is a key technology in modern photonics including application to optical manipulation of quantum information. The requisite is to obtain large rotation in isotropic media with small loss. We report on extraordinary optical activity in a planar dielectric on-waveguide photonic crystal structure, which has no in-plane birefringence and shows polarization rotation of more than 25 degrees for transmitted light. We demonstrate that in the planar chiral photonic crystal, the coupling of the normally incident light wave with low-loss waveguide and Fabry-Pérot resonance modes results in a dramatic enhancement of the optical activity.

Optical parametric oscillation out to 6.3 μm in periodically poled lithium niobate under strong idler absorption

The very high gains, achieved when using mode-locked pulses to synchronously pump an optical parametric oscillator based on periodically poled lithium niobate, permit oscillation even with strong idler absorption. Oscillation has been achieved at idler wavelengths out to 6.3 μm. Idler power was directly measured, out to 5.41 μm. Beyond this, idler generation was inferred from the observed signal. We present an analysis of operation in the presence of strong idler absorption.

A macroscopic formalism to describe the second-order nonlinear optical response of nanostructures

We present a macroscopic formalism to describe the second-order nonlinear optical response of nanostructures. Rapid variations in local nonlinearity and electric field distributions on scales smaller than a wavelength preclude a simple, direct relationship between the macroscopic and nanoscopic nonlinear response functions in arrays of metal nanoparticles. We develop an approach that bypasses these difficulties by focusing on the macroscopic nonlinear optical response of the sample in terms of the input and output fields. The main advantage of this macroscopic formalism is that it naturally includes contributions from higher multipoles, although symmetry properties can be addressed using electric-dipole-type selection rules. It is limited by being specific to the experimental geometry, although experimental variations are expected to provide additional insight into the underlying physical processes. The formalism is applied to the second-harmonic response of an array of L-shaped gold nanoparticles.