Design of a 2 diopter holographic progressive lens.

In this contribution, we investigate the use of holographic optical elements (HOEs) as progressive addition lenses (PALs). We design HOEs with high diffraction efficiency (DE) using the Fourier Modal Method (FMM) and optimize an optical system comprising two of these HOEs to fulfill the optical function of a 2 diopter (dpt) PAL. The resulting design is a holographic PAL (hPAL) exhibiting high DE and limited angular color error (CE) with a distribution of spherical power and astigmatism equivalent to its refractive counterpart. To our knowledge, our contribution is the first complete design of an hPAL. While our HOE design method is shown for PALs here, it has the potential to improve other applications of HOEs as well.

Simulating multiple diffraction in imaging systems using a path integration method.

We present a method for simulating multiple diffraction in imaging systems based on the Huygens-Fresnel principle. The method accounts for the effects of both aberrations and diffraction and is entirely performed using Monte Carlo ray tracing. We compare the results of this method to those of reference simulations for field propagation through optical systems and for the calculation of point spread functions. The method can accurately model a wide variety of optical systems beyond the exit pupil approximation.

Plasmonic modes of extreme subwavelength nanocavities.

We study the physics of a new type of subwavelength nanocavities. They are based on U-shaped metal-insulator-metal waveguides supporting the excitation of surface plasmon polaritons. The nanocavity arrays are excited by plane waves at either a normal or oblique incidence. Because of their finite length, discrete modes emerge within the nanocavity. We show that the excitation symmetry with respect to the cavity ends permits the observation of even and odd modes. Our investigations include near- and far-field simulations and predict a strong spectral far-field response of the comparably small nanoresonators. The strong near-field enhancement observed in the cavity at resonance might be suitable to increase the efficiency of nonlinear optical effects and quantum analogies and might facilitate the development of optical elements, such as active plasmonic devices.

Investigation on the second part of the electromagnetic SERS enhancement and resulting fabrication strategies of anisotropic plasmonic arrays.

In general, the electromagnetic mechanism is understood as the strongest contribution to the overall surface-enhanced Raman spectroscopy (SERS) enhancement. Due to the excitation of surface plasmons, a strong electromagnetic field is induced at the interfaces of a metallic nanoparticle leading to a drastic enhancement of the Raman scattering cross-section. Furthermore, the Raman scattered light expierences an emission enhancement due to the plasmon resonances of the nanoantennas. Herein, this second part of the electromagnetic enhancement phenomenon is investigated for different Raman bands of crystal violet by utilizing the anisotropic plasmonic character of gold nanorhomb SERS arrays. We aim at evaluating the effects of localized and propagating surface plasmon polariton modes as well as their combination on the scattered SERS intensity. From that point of view, design and fabrication strategies towards the fabrication of SERS arrays for excitation wavelengths in the visible and near-infrared (NIR) spectral region can be given, also using a double-resonant electromagnetic enhancement.

Ultrafast plasmon dynamics and evanescent field distribution of reproducible surface-enhanced Raman-scattering substrates.

Surface-enhanced Raman scattering (SERS) is a potent tool in bioanalytical science because the technique combines high sensitivity with molecular specificity. However, the widespread and routine use of SERS in quantitative biomedical diagnostics is limited by tight requirements on the reproducibility of the noble metal substrates used. To solve this problem, we recently introduced a novel approach to reproducible SERS substrates. In this contribution, we apply ultrafast time-resolved spectroscopy to investigate the photo-induced collective charge-carrier dynamics in such substrates, which represents the fundamental origin of the SERS mechanism. The ultrafast experiments are accompanied by scanning-near field optical microscopy and SERS experiments to correlate the appearance of plasmon dynamics with the resultant evanescent field distribution and the analytically relevant SERS enhancement.

The origin of magnetic polarizability in metamaterials at optical frequencies - an electrodynamic approach.

We explain the origin of the electric and particular the magnetic polarizabiltiy of metamaterials employing a fully electromagnetic plasmonic picture. As example we study an U-shaped split-ring resonator based metamaterial at optical frequencies. The relevance of the split-ring resonator orientation relative to the illuminating field for obtaining a strong magnetic response is outlined. We reveal higher-order magnetic resonances and explain their origin on the basis of higher-order plasmonic eigenmodes caused by an appropriate current flow in the split-ring resonator. Finally, the conditions required for obtaining a negative index at optical frequencies in a metamaterial consisting of split-ring resonators and wires are investigated.