Analysis and magnetic modulation of chiro-optical properties in anisotropic chiral and magneto-chiral plasmonic systems

Abstract

We present a systematic study to separate the different contributions to the dichroic response of complex plasmonic split-ring/ring magneto-chiral systems. For this, we first construct metastructures with plasmonic, chiral and magneto-optical functionalities by specific arrangements of different building blocks, each of them responsible for one of the functionalities. Then, by the use of Mueller matrices in forward/backward spectroscopic measurements under magnetic field, we separate optical anisotropy from pure chiral contributions to the overall dichroic response of the system. This allows determining the pure chiral response of the structures and the corresponding magnetic field modulation mediated by the magneto-optical effect present in the corresponding building block, which reaches values of 25% at 740 nm. This fabrication and characterization procedure, assigning the different optical functionalities to different building blocks, and decomposing the different contributions to the global optical response, allows an easy and rational identification of the different phenomena exhibited by the magneto-chiral system.

Nanoscale magnetophotonics

“…Along this direction, it is worth mentioning that a detailed analysis which might help to reach this goal was reported by Feng et al [137], where they analyzed the contributions from optical chirality, optical anisotropy and magnetic modulation of circular dichroism (CD) to the global optical response in Au/Co split-ring geometries. In this particlaur case they showed a system which have a strong chiral response with a MO-mediated magnetic modulation of CD of about 25% [ Fig.…”

Mueller matrix study of the dichroism in nanorods dimers: rod separation effects

“…From symmetry considerations, we have used a valid method based on measurements with sample illumination from the metastructures side (Front-F) or from the substrate side (Back-B) [29,30]. This allows, for example, to discern the different contributions of the system to the circular differential extinction [26,31]. The sample was mounted on a rotational stage which allows changing the in-plane orientation of the sample.…”

“…The same occurs for the circular differential extinction value, m 14 mmetry of depend on is system nation of c circular dichroism (CD in ). It is known that, in complex systems with small anisotropies where these two effects (optical anisotropy and intrinsic circular dichroism) coexist, it is possible to separate their contributions to the CDE by carrying out forward and backward experimental measurements, since these two magnitudes behave differently for forward and backward illumination [26,33]. The experimentally measured circular differential extinction can be decomposed in the intrinsic circular dichroism and optical anisotropy components (CDE = CD in + OA) where 14…”

Enhanced magnetic modulation of light polarization exploiting hybridization with multipolar dark plasmons in magnetoplasmonic nanocavities

“…Additionally, light propagation in the presence of magneto-optical materials becomes non-reciprocal due to the time-reversal symmetry breaking caused by magnetization, which is an axial time-odd vector field. Therefore, in the past decade, materials based on magnetoplasmonic nanoantennas have been intensively investigated for their enhanced MO and non-reciprocal light propagation properties, aiming for 2D flat-optics nanodevices, such as rotators, modulators, and isolators 8,10,[13][14][15][16][17][18][19][26][27][28][29] , as well as for their accuracy in the measurement of distances at the nanoscale 30 and very small refractive index changes in label-free biosensing applications 7,11,[31][32][33][34][35] .…”

“…Therefore, the maximum achievable enhancement of the MO activity can be up to only~1-order of magnitude using the magnetoplasmonic nanoantenna designs explored thus far [6][7][8][9][10][11][12][13][14][15][16][17][18][19] . This Q-limited enhancement of MO activity triggered the exploration of different geometries such as, for example, heterogeneous noble and ferromagnetic vertical dimers [39][40][41] and split-ring resonators combining plasmonic and magnetic materials, with the latter as an integrating part of the ring 29,42 . Although these systems displayed resonances with an improved Q-factor, the physics governing their electrodynamics connected to the MO activity still relies on the excitation of bright plasmons as in conventional magnetoplasmonic structures.…”