Todd P. Meyrath

Optical resonances of bowtie slot antennas and their geometry and material dependence

In order to provide a guide for the design and optimization of bowtie slot antennas in the visible and near infrared spectral regime, their optical properties have been investigated with emphasis on geometry and materials. Although primarily theoretical, experimental investigations for reduced thickness cases are also included. As characterized by their field patterns, two types of resonances are discussed: plasmonic and Fabry-Pérot-like resonances. These resonance types show a linear dependence on aperture perimeter and film thickness, respectively, while showing a complementary behavior with near independence of the other respective parameter. Metal properties, as in the Drude model, are also considered. Various metals with respectively different skin depths are studied, showing a nearly linear dependence of the resonance wavelength on skin depth.

Resonance hybridization in double split-ring resonator metamaterials

We introduce a plasmon hybridization picture to understand the optical properties of double split-ring resonator metamaterials. The analysis is based on the calculated reflectance spectra from a finite-integration time-domain algorithm. Field distributions of the double split-ring resonators at the resonant frequencies confirm the results from the plasmon hybridization analysis. We demonstrate that the plasmon hybridization is a simple and powerful tool for understanding and designing metamaterials in the near infrared and visible regime.

Spiral-type terahertz antennas and the manifestation of the Mushiake principle

We report on the experimental and theoretical study of the resonant eigenmodes of spiral-type terahertz antennas. The analysis is carried out for a varying number of spiral windings. For larger numbers the structure possesses a self-complementary property which allows the application of the Mushiake principle predicting that the impedance of such structures is half the impedance of free space. This permits to observe an equal and frequency independent reflection and transmission coefficient. This property makes the spiral-type terahertz antenna not only a fascinating example of a medium supporting strong resonances in the long wavelength limit but also a medium which can be easily and reasonably homogenized at higher frequencies. This is in stark contrast to most of the existing metamaterials.

Resonances in complementary metamaterials and nanoapertures

We theoretically analyze the properties of metamaterials which have been designed by taking advantage of Babinets principle. It is shown that the complementary structure exhibits both a complementary spectral response and field distribution of the respective eigenmodes. For complementary split-ring resonators, we show that the spectral resonance features can be explained from two different perspectives. On one hand they can be explained as plasmon polariton resonances in dielectric nanostructures surrounded by metal, on the other hand they can be understood as guided mode resonances with vanishing propagation constant. The physical origin of these modes and differences to the conventional split-ring geometry are discussed.

Thermal lensing in an end-pumped Yb:KGW slab laser with high power single emitter diodes.

We demonstrate that it is possible to pump an Ng-cut Yb:KGW crystal slab with up to 18W by a single emitter laser diode and still achieve a nearly diffraction limited output beam with a M(2) value below M(2) < 1.1 and optical to optical efficiencies of more than 44%. Furthermore, we have measured the focal length of thermally induced lenses in an Yb:KGW crystal slab which was end-pumped by 12 W and 18 W single-emitter diodes. We have observed that the focal lengths not only depend on the pump power and beam waists, but are also dependent on the specific diode beam profile, as well as the collimation optics. We have been able to correlate this behavior with specific patterns of the beam profile.

A hydrogen sensor based on metallic photonic crystal slabs

A hydrogen sensor based on a metallic photonic crystal using gold and WO3 is presented. Hydrogen exposure influences the optical properties of this device by gasochromic mechanisms with a theoretical limit in the sub-1000-ppm-range.

Optical hydrogen sensing with metallic photonic crystals and plasmonic metamaterials

In this contribution, we are going to present two plasmonic concepts for hydrogen sensing. Our first concept is based on metallic photonic crystals, where a gold grating together with a thin layer of Pd in combination with a waveguide of WO3 can give a strong resonance in the extinction or reflection spectrum. Upon hydrogen exposure, the WO3 undergoes a refractive index change, which will shift the spectral resonance. A suitably tuned laser or LED can interrogate this change and give an optical signal. Our second concept is based on a plasmonic metamaterial which comprises a perfect absorber. A layer made from Pd wires as placed on a spacer layer and a gold mirror. Suitable design parameters lead to a zero transmittance as well as zero reflectance for a given wavelength. Upon hydrogen exposure, this perfect absorption is distorted and reflected light can be detected.

Efficient and Simple High-Power Femtosecond Yb:KGW Slab-Laser Pumped by a Single Broad-Area Emitter Diode

We demonstrate a simple and efficient femtosecond Yb:KGW slab laser with output powers of nearly 5 W and pulse widths as short as 161 fs. It is pumped with a single broad-area emitter diode.

Two distinct types of resonances in optical bowtie slot nanoantennas

We study the resonance properties of optical bowtie slot antennas in experiment and numerical simulations. The dependence of the plasmonic and Fabry-Perot-like resonances on the antenna geometry and metal properties is investigated.