Plasmonics and Terahertz Optics
Light-matter interaction is enhanced by resonant structures such as conducting (plasmonic) structures and nanowires. Light harvesting enhanced by electromagnetic field resonances is one of the major contributions of photonics for solar energy conversion, photodetectors or sensors. Also the emission of light can be tailored in efficiency and directionality with resonant nanostructures. Strong light-matter coupling can generate new opportunities for modifying material properties relevant for photonic and optoelectronic applications. Resonant structures at THz frequencies can lead to local electromagnetic fields that can be tailored with a great precision. In PSN we investigate the interaction of light with resonant structures at optical and THz frequencies with the aim of developing novel concepts that can improve optoelectronic devices.
The field of nanophotonics concerns the study and manipulation of visible and near-IR light on length scales comparable to or smaller than its wavelength. We focus on two types of nanophotonic structures, namely, semiconductor nanowires and metallic (plasmonic) nanoparticles. In particular, we study the absorption and emission of quantum emitters coupled to collective plasmonic resonances. We are interested in the strong coupling regime in which Plasmon-Exciton-Polaritons (PEPs), i.e., hybrid light-matter quasi-particles, emerge from the coupling of optical modes supported by resonant metallic nanoparticles (surface plasmon polaritons) and excitons in materials. We use arrays of metallic nanoparticles to tailor the coupling strength between surface plasmon polaritons and excitons and in this way control the characteristics of PEPs. We also study the interaction of light with semiconductor nanowires. The geometry and the dimension comparable to the wavelength of light determine the complex interplay between light and the nanowires. We investigate this interplay with different techniques and in terms of angle-, wavelength-, and polarization-dependent emission and absorption.
THz radiation are electromagnetic waves with frequencies in THz range, i.e., the range between microwaves and far-IR. Resonant structures at THz frequencies formed by semiconductors or metals are important to control the propagation and enhancement of THz radiation. These structures respond very differently to incident radiation depending on their orientation and shape. In this way, the far- and near-field of incident radiation can be strongly modified by resonant structures, leading to enhanced or reduced extinction and to large local electromagnetic fields. We study these interactions both in the far and in the near-field using THz time domain spectroscopy and microscopy. Our goal is to tailor THz fields with subwavelength precision and to use these fields for THz spectroscopy. Optical pump-THz probe spectroscopic techniques enables the contact-free determination of the photoconductivity of materials. Therefore, we use these techniques to investigate materials relevant to energy applications.