We perform second harmonic spectroscopy of aluminum nanoantenna arrays that exhibit plasmonic resonances at the second harmonic wavelength between 450 and 570 nm by focusing sub-30 fs laser pulses tunable from 900 to 1140 nm onto the nanoantenna arrays. We find that a plasmonic resonance at the second harmonic wavelength boosts the overall nonlinear process by more than an order of magnitude. In particular, in the measurement the resonant second harmonic polarization component is a factor of about 70 stronger when compared to the perpendicular off-resonant second harmonic polarization. Furthermore, the maximum of the second harmonic conversion efficiency is found to be slightly blue-shifted with respect to the peak of the linear optical far-field spectrum. This fact can be understood from a simple model that accounts for the almost off-resonant absorption at the fundamental wavelength and the resonant emission process at the second harmonic.

We experimentally demonstrate an ultra-thin plasmonic optical rotator in the visible regime that induces a polarization rotation that is continuously tunable and switchable by an external magnetic field. The rotator is a magneto-plasmonic hybrid structure consisting of a magneto-optical EuSe slab and a one-dimensional plasmonic gold grating. At low temperatures, EuSe possesses a large Verdet constant and exhibits Faraday rotation, which does not saturate over a regime of several Tesla. By combining these properties with plasmonic Faraday rotation enhancement, a large tuning range of the polarization rotation of up to 8.46 for a film thickness of 220 nm is achieved. Furthermore, through experiments and simulations, we demonstrate that the unique dispersion properties of the structure enable us to tailor the wavelengths of the tunable polarization rotation to arbitrary spectral positions within the transparency window of the magneto-optical slab. The demonstrated concept might lead to important, highly integrated, non-reciprocal, photonic devices for light modulation, optical isolation, and magnetic field optical sensing. The simple fabrication of EuSe nanostructures by physical vapor deposition opens the way for many potentially interesting magneto-plasmonic systems and three-dimensional magneto-optical metamaterials.

We demonstrate the realization of a new hybrid magnetoplasmonic thin film structure that resembles the classical optical analog of electromagnetically induced absorption. In transmission geometry our gold nanostructure embedded in an EuS film induces giant Faraday rotation of over 14°for a thickness of less than 200 nm and a magnetic field of 5 T at T ¼ 20 K. By varying the magnetic field from −5 to þ5 T, a rotation tuning range of over 25°is realized. As we are only a factor of 3 away from the Faraday isolation requirement, our concept could lead to highly integrated, nonreciprocal photonic devices for light modulation, optical isolation, and optical magnetic field sensing.

The Faraday effect describes the phenomenon that a magnetized material can alter the polarization state of transmitted light. Interestingly, unlike most light-matter interactions in nature, it breaks Lorentz reciprocity. This exceptional behavior is utilized for applications such as optical isolators, which are core elements in communication and laser systems. While there is high demand for sub-micron nonreciprocal photonic devices, the realization of such systems is extremely challenging as conventional magneto-optic materials only provide weak magnetooptic response within small volumes. Plasmonics could be a key to overcome this hurdle in the future: over the last years there have been several lines of work demonstrating that different types of metallic nanostrutures can be utilized to greatly enhance the magneto-optic response of conventional materials. In this review we give an overview over the state of the art in the field and highlight recent developments on hybrid plasmonic Faraday rotators. Our discussions are mainly focused on the visible and near-infrared wavelength regions and cover both experimental realizations as well as analytical descriptions. Special attention will be paid to recent developments on hybrid plasmonic thin film systems consisting of gold and europium chalcogenides.

Using localized surface plasmons, the magneto-optical response of dielectric thin films can be resonantly amplified and spectrally tailored. While the experimental realization and numerical simulation of such systems received considerable attention, so far, there is no analytical theoretical description. Here, we present a simple, intrinsically Lorentz nonreciprocal coupled oscillator model that reveals the underlying physics inside such systems and yields analytical expressions for the resonantly enhanced magneto-optical response. The predictions of the model are in good agreement with rigorous numerical solutions of Maxwell's equations for typical sample geometries. Our ansatz is transferable to other complex and hybrid nanooptical systems and will significantly facilitate device design.