Modern optical systems are subject to very restrictive performance, size and cost requirements. Especially in portable systems size often is the most important factor, which necessitates elaborate designs to achieve the desired specifications. However, current designs already operate very close to the physical limits and further progress is difficult to achieve by changing only the complexity of the design. Another way of improving the performance is to tailor the optical properties of materials specifically to the application at hand. A class of novel, customizable materials that enables the tailoring of the optical properties, and promises to overcome many of the intrinsic disadvantages of polymers, are nanocomposites. However, despite considerable past research efforts, these types of materials are largely underutilized in optical systems. To shed light into this issue we, in this paper, discuss how nanocomposites can be modeled using effective medium theories. In the second part, we then investigate the fundamental requirements that have to be fulfilled to make nanocomposites suitable for optical applications, and show that it is indeed possible to fabricate such a material using existing methods. Furthermore, we show how nanocomposites can be used to tailor the refractive index and dispersion properties towards specific applications..
Progressive addition lenses (PALs) are realized as optical freeform surfaces by complex manufacturing and inspection processes. In turn, holographic optical elements (HOEs) enable fast and easy fabrication in other applications. Here we present a design method for the combination of both; HOEs that are designed to fulfill the optical function of PALs. We describe how inherent limitations of HOEs, such as angular and wavelength selectivity as well as grating dispersion can be overcome. We show that holographic PALs can be optimized to have a distribution of spherical power and astigmatism, which is a qualitative replication of the performance of their refractive counterparts. The design rules we identify are shown for PALs but have the potential to improve other applications of HOEs as well.
We study a simulation method that uses the Wigner distribution function to incorporate wave optical effects in an established framework based on geometrical optics, i.e., a ray tracing engine. We use the method to calculate point spread functions and show that it is accurate for paraxial systems but produces unphysical results in the presence of aberrations. The cause of these anomalies is explained using an analytical model.
The influence of the lateral asymmetry of the double-wires on the macroscopic effective parameters of the
metamaterial was investigated using the multipole model. Investigations have shown that the system dynamics
is dominated by the largest wire, which plasmonic oscillations define the orientation and the strength of the
microscopic currents in the system. As a result the magnetization of the material can be enhanced for certain
asymmetric configurations of the constitutive double-wires.
Metamaterials are composites consisting of artificial
meta-atoms/metamolecules with typical sizes less than the
wavelength of operation. One of the key properties that makes metamaterials distinctly different form the natural media is
a very strong magnetic response that can be engineered in the visible and infra-red part of the spectrum.
In this work we summarize our multipole expansion approach that can be used to describe analytically optical properties
of metamaterials composed of, in particular, the split-ring and
cut-wire resonators. An important feature of our
formalism is the possibility of describing nonlinear response of a metamaterial, such as second harmonic generation,
which arises due to induced high-order multipoles.
Our model has recently been extended to the case of hybrid metamaterials composed of plasmonic nano-resonators
coupled with quantum elements (such as quantum dots, carbon nano tubes etc). It has also been shown that apart from
metamaterials various other physical systems can be successfully modelled within framework of the developed approach.
For example, transient dynamics and steady-state regime of a
nano-laser, as well as its stochastic properties (e.g.
linewidth of generation) have been described using this model.
Plasmonic nanostructures exhibit a strong field enhancement due to the excitation of localized and propagating surface
plasmon polaritons. The use of these effects yields in a wide range of analytical applications. For instance, the strong
electromagnetic field enhancement may be used to dramatically increase fluorescence, Raman cross sections (surface
enhanced Raman spectroscopy - SERS) or IR absorption. Since the requirements to a powerful technique are both a
fingerprint specificity and high sensitivity, the SERS method is a powerful tool for a variety of analytical applications in
(bio)chemical and biological analysis. Because the reproducibility of established SERS arrays (e. g. roughened metal
electrodes and aggregated metal nanoparticle) across a large measuring area is rather low, we have established an e-beam
(electron beam lithography) based fabrication process yielding in regularly patterned gold nanorhomb arrays. The
anisotropic optical response of the SERS array is characterized. Furthermore, the SERS arrays are investigated with
respect to the second part of their electromagnetic enhancement, resulting in design and fabrication criteria of potential
A simple analytical model has been developed within the scopes of the macroscopic Maxwell's equations. In the
framework of this model the dispersion relation for plane waves has been calculated for the case of Cut-Wire (CW) and
Split Ring Resonator (SRR) geometries. The dispersion relation has been compared with rigorous numerical calculations.
A possible way to introduce the electric and magnetic material parameters has been suggested. Validity criteria and
applicability limitations of the developed model are discussed. A new type of nonlinearity specific for the metamaterials
- Multipole Nonlinearity - is identified based on the developed model, wheras the second harmonic generation (SHG)
process is considered in detail
An analytical description for plane wave propagation in metamaterials (MM) is presented. It follows the usual
approach for describing light propagation in homogenous media on the basis of Maxwell's equations, though
applied to a medium composed of metallic nanostructures. Here, as an example, these nanostructures are double
(or cut) wires. In the present approach the multipole expansion technique is used to account for the electric and
magnetic dipole as well as the electric quadrupole moments of the carrier distribution within the nanostructure
where a model of coupled oscillators is used for the description of the internal charge density dynamics. It is
shown how expressions for the effective permittivity and permeability can be derived from analytical
expressions for the dispersion relation, the magnetization and the electric displacement field. Results of the
analytical model are compared with rigorous simulations of Maxwell's equations yielding the limitations and
applicability of the proposed model.
The properties of metamaterials made of an increasing number of discrete functional layers are analyzed.
Convergence of the effective properties towards their bulk counterparts is observed if the light propagation in the
metamaterial is dominated by a single eigenmode. The effective properties of the finite structure will be
compared to the properties of the infinite structure for which an effective refractive index can be derived from
the dispersion relation. The dispersion relation is furthermore shown to be useful in deriving angle dependent
effective material parameters. They are compared to the effective properties obtained from a finite slab by
applying a dedicated retrieval procedure.
High transparent thermoplastics have the capability to put glass out of business, especially in everyday life's optics. Their diverse nature gives rise to different antireflection principles. The reduction of surface reflection losses in polymethylmethacrylate (PMMA) is demonstrated by means of argon/oxygen plasma treatment. Since the presented reduction of reflection occurs in a wide spectral range, the technique may be applied for omnidirectional devices or curved substrates. The etching process creates a self-organized stochastic subwavelength structure at the substrate itself. The decrease in reflection is described by effective medium theory (EMT), converting the surface topology into a depth-dependent filling factor profile. In a second step this nano-scaled structure is used as the initial point for a broadband absorber by coating it with a nontransparent metal layer. A high-efficient absorber can be obtained, if the metal acts as backside coating of the double-sided plasma-treated substrate and steady-going transitions between the materials eliminating the Fresnel reflections. In practice, the magnitude of absorption depends on depth of structure as well as on the complex refractive index of the metal.