Gold triple-helix mid-infrared metamaterial by STED-inspired laser lithography.

In analogy to wire-grid polarizers for linear polarization, metal-helix metamaterials can act as broadband circular polarizers. This concept has brought circular-polarization capabilities to mid-infrared and terahertz frequencies, which were previously difficult to access. Due to the lack of rotational symmetry, however, single-helix metamaterials exhibit unwanted circular-polarization conversions.

Tapered N-helical metamaterials with three-fold rotational symmetry as improved circular polarizers.

Chiral helix-based metamaterials can potentially serve as compact and broadband circular polarizers. We have recently shown that the physics of structures composed of multiple intertwined helices, so called N-helices with N being an integer multiple of 4, is distinct from that of structures made of single circular helices (N = 1). In particular, undesired circular polarization conversion is strictly eliminated for N = 4 helices arranged on a square lattice.

Dip-in depletion optical lithography of three-dimensional chiral polarizers.

We combine the concepts of dip-in and stimulated-emission-depletion-inspired optical lithography for the first time to fabricate three-dimensional (3D) nanostructures for photonics. For depletion of the photoinitiator ITX we employ a fiber-coupled laser diode at 639 nm wavelength. To demonstrate the performance of the experimental setup, we have fabricated 3D chiral layer-by-layer twisted woodpile structures with a lattice constant reduced by more than a factor of 2 compared to earlier results.

Three-dimensional multi-photon direct laser writing with variable repetition rate.

We perform multi-photon direct laser writing as a function of laser repetition rate over many orders of magnitude and otherwise unchanged experimental conditions. These new data serve as basis for investigating the influence of different proposed mechanisms involved in the photopolymerization: two-photon absorption, photoionization, avalanche ionization and heat accumulation. We find different non-linearities for high and low repetition rates consistent with different initiation processes being involved.

Three-dimensional microscaffolds exhibiting spatially resolved surface chemistry.

Spatial control over the surface chemistry of 3D organic-inorganic hybrid microscaffolds is achieved by a two-photon-triggered cycloaddition. Following a coating step with photoactivatable dienes via silanization, surface irradiation with a femtosecond-pulsed laser in the presence of functional dienophiles enables a site-selective alteration of the surface chemistry. Bioconjugation with fluorescent protein tags is employed to reveal the 3D molecular patterns.

Three-dimensional quantum photonic elements based on single nitrogen vacancy-centres in laser-written microstructures.

To fully integrate quantum optical technology, active quantum systems must be combined with resonant microstructures and optical interconnects harvesting and routing photons in three diemsnsions (3D) on one chip. We fabricate such combined structures for the first time by using two-photon laser lithography and a photoresist containing nanodiamonds including nitrogen vacancy-centers. As an example for possible functionality, single-photon generation, collection, and transport is successfully accomplished.

On metamaterial circular polarizers based on metal N-helices.

Metal-helix based metamaterials have been introduced as compact and broadband circular polarizers. However, the end of the metal wire together with the helix center defines an axis in space, which unavoidably breaks the rotational symmetry at the metamaterial surface. This introduces linear birefringence.

Tailored 3D mechanical metamaterials made by dip-in direct-laser-writing optical lithography.

Dip-in direct-laser-writing (DLW) optical lithography allows fabricating complex three-dimensional microstructures without the height restrictions of regular DLW. Bow-tie elements assembled into mechanical metamaterials with positive/zero/negative Poisson's ratio and with sufficient overall size for direct mechanical characterization aim at demonstrating the new possibilities with respect to rationally designed effective materials.