Roope Siikanen

Metamaterials with tailored nonlinear optical response.

We demonstrate that the second-order nonlinear optical response of noncentrosymmetric metal nanoparticles (metamolecules) can be efficiently controlled by their mutual ordering in an array. Two samples with minor change in ordering have nonlinear responses differing by a factor of up to 50. The results arise from polarization-dependent plasmonic resonances modified by long-range coupling associated with metamolecular ordering. The approach opens new ways for tailoring the nonlinear responses of metamaterials and their tensorial properties.

Second-harmonic generation from metal nanoparticles: resonance enhancement versus particle geometry.

We demonstrate that optical second-harmonic generation (SHG) from arrays of noncentrosymmetric gold nanoparticles depends essentially on particle geometry. We prepare nanoparticles with different geometrical shapes (L and T) but similar wavelengths for the polarization-dependent plasmon resonances. In contrast to recent interpretations emphasizing resonances at the fundamental frequency, the T shape leads to stronger SHG when only one, instead of both, polarization component of the fundamental field is resonant. This is explained by the character of plasmon oscillations supported by the two shapes. Our numerical simulations for both linear and second-order responses display unprecedented agreement with measurements.

Spectral control in anisotropic resonance-domain metamaterials.

We introduce a concept to control the spectral and dichroic properties of metamaterials. The approach is based on anisotropic metal nanoparticles and on varying their mutual orientation in a periodic lattice. Even seemingly inconsequential changes in particle ordering strongly modify the dichroic properties of the arrays and result in either very narrow resonances or ultrabroad extinction ranges. The results arise from long-range diffractive coupling between the particles, as determined by the dependence of the array unit cell size on particle ordering.

Metamaterials with Tailorable Nonlinear Optical Properties

Second-order nonlinear processes such as second-harmonic generation (SHG) require noncentrosymmetric structures. The development of second-order metamaterials, however, has been hampered by symmetry breaking due to sample defects and shape distortions. The resulting outcomes can be interpreted in terms of effective higher-multipole (magnetic and quadrupole) effects that strongly modify the radiative properties of the samples.

Enhancement of second-harmonic generation from gold nanoparticles through passive elements

Summary form only given. Antennas are devices that enable the coupling of electromagnetic radiation from a source into the far field or vice versa [1]. Recent advances in nanofabrication have allowed antenna concepts to be moved from the radio-frequency to the optical domain [2]. Passive elements play an important role in the design of antennas, usually used to improve the directionality of radiation from the antennas. In this Paper, we show that the presence of passive elements enhances the efficiency of second-harmonic generation (SHG).

Ways to optimize the second-harmonic response from metamaterials

Metamaterials consisting of metal nanoparticles offer the possibility to engineer the nonlinear optical properties by varying their plasmonic resonances. The resonances depend on the size, shape, and dielectric environment of the particles as well as their mutual ordering. We show several ways of controlling and optimizing the second-harmonic response of plasmonic metamaterials.

Resonance-domain effects in second-harmonic generation from metal nanostructures

Summary form only given. We study second-harmonic generation from arrays of anisotropic metal nanoparticles (metamolecules) as a function of their mutual arrangement. The overall second-harmonic response of such samples cannot be simply described by the orientational average of the individual metamolecules. Instead, the response can vary by more than an order of magnitude for the same average orientational distribution depending on the detailed ordering of the metamolecules in the array. The results are explained by diffractive long-range coupling between the metamolecules.