Evgeniy A. Mamonov

Two‐Photon Luminescence and Second‐Harmonic Generation in Organic Nonlinear Surface Comprised of Self‐Assembled Frustum Shaped Organic Microlasers

An ultrathin nonlinear optical (NLO) organic surface composed of numerous self-assembled frustum-shaped whispering-gallery-mode resonators displays both two-photon luminescence and second-harmonic-generation signals. A super-second-order increase of the NLO intensity with respect to pump power confirms the microlasing action and practical usefulness of the NLO organic surfaces.

Chirality in nonlinear-optical response of planar G-shaped nanostructures

Chirality effects in optical second harmonic generation (SHG) are studied in periodic planar arrays of gold G-shaped nanostructures. We show that G-shaped structures of different handedness demonstrate different SHG efficiency for the left and right circular polarizations, as well as the opposite directions of the SHG polarization plane rotation. The observed effects are interpreted as the appearance of chirality in the SHG response which allows clear distinguishing of two enantiomers.

Coherent and incoherent second harmonic generation in planar G-shaped nanostructures

Azimuthal anisotropy of Stokes parameters of the second harmonic generation (SHG) generated and observed in reflection from a periodic planar area of G-shaped gold nanostructures is studied. A strong anisotropy of both coherent and incoherent SHG components is observed. Finite-difference time-domain calculations prove that the observed effects are due to the anisotropic enhancement of the fundamental radiation within the G-shaped structures.

Chiral organic photonics: self-assembled micro-resonators for an enhanced circular dichroism effect in the non-linear optical signal

Chiro-optical signals from chiral molecules/structures are inherently weak. In particular, enhancing the circular-dichroism (CD) effect (different absorption of left or right circularly polarized light) in the non-linear optical (NLO) signal from chiral molecular materials is challenging and imperative since it is advantageous in various areas, from biomedical sciences to miniaturized photonic devices. Here we suggest and realize for the first time an approach to enhance the CD effect taking advantage of the NLO effects resonantly enhanced in the nonlinear chiral organic micro-resonators. These R- and S-type resonators in the form of micro-spheres are prepared by the self-assembly technique from the corresponding axially chiral enantiomeric molecules, namely R- and S-4-[2,2′-diethoxy-6′-(4-formylphenyl)-[1,1′-binaphthalen]-6-yl]benzaldehyde in CHCl3/MeOH mixtures. Each enantiomeric micro-sphere, upon optical pumping, acts as a whispering gallery mode (WGM) resonator as the photo-luminescence (PL) is excited in a single- or in a two-photon regime. We show that the NLO-CD effect and the two-photon absorption (TPA) in the case of micro-spheres are at least twice as high as compared to a continuous film of the same effective thickness. This is due to pronounced field localization effects in micro-spheres with high Q-factor, which increases the photon residence time (τP) in a chiral medium and thus strengthens the light–matter interaction. Finite-difference time-domain (FDTD) numerical calculations confirm a strong light localization near the boundary of the micro-spheres.

Enhanced magnetic second-harmonic generation from resonant metasurfaces

We demonstrate enhancement of second-harmonic generation efficiency in sub-wavelength resonant nanostructures supporting optically induced magnetic response. This is achieved through simultaneous excitation of electric and magnetic multipoles at the second-harmonic wavelength and their constructive interference.

Second harmonic generation in planar chiral nanostructures

The effect of the chirality of planar spiral nanostructures on optical second harmonic generation (SHG) is studied in the paper. It is shown that the intensity of left and right circularly polarized SHG differs for structures of different handedness and the direction of the SHG polarization rotation plane is opposite for enantiomers.

Circular dichroism in optical second harmonic generated in reflection from chiral G-shaped metamaterials

Influence of chirality on the optical second harmonic generated from planar array of G-shaped metamaterials is studied. Circular dichroism of these nanostructures manifests itself via different efficiency of left and right circularly polarized second harmonic that is observed for the samples of different handedness. This difference allows to distinguish between the two enantiomers.

Optical second harmonic generation from chiral nanostructures

Recent technological achievements provide unique possibilities for the composition of arrays of nanostructures with desired properties, nowadays referred to as metamaterials, that are perspective for various applications. A special place here belongs to chiral nanostructures that could compete with the natural materials both in efficiency and size of functional elements. For the case of metamaterials, optical activity originates from a special shape of the elements and their arrangement within an array. This research field has been actively developing over the last years and significant values of chirality effects were observed in the linear-optical response of metallic nanostructures [1]. Furthermore, chirality effects are more pronounced in the nonlinear-optical response of such structures [2, 3], the latter being governed to a great extent by the local field distribution inside the metal nanostructures. In this talk we will focus mostly on the recent results on the linear and nonlinear optical effects in planar arrays of chiral nanostructures with the shape of a flat spiral (G-shaped nanostructures).

Nonlinear optical effects in organic microstructures

Organic microstructures attract much attention due to their unique properties originating from the design of their shape and optical parameters. In this work we discuss the linear, second- and third-order nonlinear optical effects in arrays and in individual organic microstructures composed by self-assembling technique and formed randomly on top of a solid substrate. The structures under study consist of micro-spheres, -hemispheres or -frustums made of red laser dye and reveal an intense fluorescence (FL) in the visible spectral range. Importantly, that due to a high value of the refractive index and confined geometry, such micro-structures support the excitation of whispering gallery modes (WGM), which brings about strong and spectrally-selected light localization. We show that an amplification of the nonlinear optical effects is observed for these structures as compared to a homogeneous dye film of similar composition. The obtained data are in agreement with the results of the FDTD calculations performed for the structures of different dimensions. Perspectives of application of such type of organic nonlinear microresonators in optical devices are discussed.

Studies of short pulse propagation in 1D porous silicon based photonic crystals with spatially modulated photonic band gap

We study the propagation and periodical regeneration of short laser pulses in 1D porous silicon based photonic crystals (PC) with spatially modulated photonic band gap. The effective potential of this PC is analogous to that of an optical harmonic oscillator. The results of computer simulations of this effect and optical properties of the composed PC with the corresponding photonic band gap are discussed.