Jesper Serbin

Fabrication of woodpile structures by two-photon polymerization and investigation of their optical properties

Two-photon polymerization (2PP) is a powerful technique for the fabrication of 3D micro- and submicro-structures. By applying laser powers that are only slightly above the polymerization threshold, 3D structuring of photosensitive materials with a resolution down to 100 nm can be realized. Here we report on woodpile photonic crystal structures fabricated in organic-inorganic hybrid polymers (Ormocers) and investigation of their optical properties. The fabricated crystals possess a photonic band gap in the near infrared spectral region. The polymeric woodpile structures can be used as templates for the fabrication of highly refractive TiO2 replicas. First results in this direction are presented.

Femtosecond lasers as novel tool in dental surgery

Abstract There is a proven potential of femtosecond lasers for medical applications like cornea shaping [1] , ear surgery or dental surgery [2] . Minimal invasive treatment of carious tissue has become an increasingly important aspect in modern dentistry. State of the art methods like grinding using turbine-driven drills or ablation by Er:YAG lasers [3] generate mechanical and thermal stress, thus generating micro cracks of several tens of microns in the enamel [4] . These cracks are starting points for new carious attacks and have to be avoided for long term success of the dental treatment. By using femtosecond lasers (1 fs =10 −15 s ) for ablating dental tissue, these drawbacks can be overcome. We have demonstrated that femtosecond laser ablation offers a tool for crack-free generation of cavities in dental tissue. Furthermore, spectral analysis of the laser induced plasma has been used to indicate carious oral tissue. Our latest results on femtosecond laser dentistry will be presented, demonstrating the great potential of this kind of laser technology in medicine.

Superprism phenomena in waveguide-coupled woodpile structures fabricated by two-photon polymerization.

Here we give theoretical as well as experimental evidence for wavelength dependent super-refraction phenomena in waveguide coupled superprisms based on polymer woodpile structures. The photonic crystals were fabricated by means of the two-photon polymerization technique and have a partial band gap at near infrared wavelengths. To visualize the superprism effect the light propagating inside the woodpile structure was imaged using a CCD for a continuous range of wavelengths slightly above the band gap frequency. We were able to demonstrate a change of propagation direction from +50 degrees (positive refraction) to -10 degrees (negative refraction) with respect to the crystal surface normal for a wavelength range between 860 nm and 960 nm. Our results show the great potential of these low refractive index three-dimensional crystals, fabricated in a very fast and single-step process, to serve directly as functional micro-optical devices in the near infrared wavelength regime.

Use of two-photon polymerization for continuous gray-level encoding of diffractive optical elements

Generation of continuous gray levels in three-dimensional diffractive optical elements has remained a challenge with the current semiconductor microfabrication method. In this letter, the authors propose and demonstrate the use of the two-photon polymerization method for fabricating three-dimensional diffractive optical elements of continuous gray levels. This method is a mask-free and low-cost single-step process. It is shown that the multilevel-phase-encoded diffractive optical element fabricated in inorganic-organic hybrid polymer material facilitates the intensity distribution synthesis with a high diffraction efficiency approaching the theoretical limit.

Three-dimensional nanostructuring with femtosecond laser pulses

The development of simple laser-based technologies for the fabrication of complicated three-dimensional (3-D) microstructures with a structure size down to 100 nm is reported. These technologies are based on nonlinear multiphoton laser-matter interaction processes allowing to overcome the diffraction limit and to fabricate 3-D structures inside transparent materials. Examples on nanostructuring of metals, dielectrics, and polymers are presented.

Advanced packaging materials for optical applications : bridging the gap between nm-size structures and large-area panel processing

During the last two decades, nano-materials have been intensively investigated due to their wide range of properties, resulting in a variety of applications. In order to serve as advanced packaging material, from an industrial point of view emphasis has also to be on cost reduction either for the materials, the processes, or for both. Materials are searched for which enable processing and integration from a nm up to a cm scale. A particular class of low-cost nanoscale materials fulfilling this requirement are inorganic-organic hybrid polymers (ORMOCER®)1 which are synthesized by catalytically controlled hydrolysis/polycondensation reactions, resulting in storage-stable resins. Due to the variety of chemical and physical parameters, the material and processing properties which directly influence the resulting structure and thus the physical properties, can be varied over wide ranges. Upon synthesis, functional organic groups are introduced into the material which allows one to photochemically pattern the resins. The materials are capable to be patterned on a nm up to a cm scale, employing a variety of different micro- and nanopatterning methods such as, UV lithography, UV replication/lithography, laser-direct writing, or two-photon polymerization, in order to generate micro- and nano-optical components. While for most of the techniques the patterning has to be repeated several times in order to achieve multi-functional layers, the latter method allows one to directly write arbitrary 3D structures into the hybrid polymer material. The combination of chemically designed low-cost materials with tunable material parameters such as low optical absorption, tunable refractive index, good processibility, and high chemical, thermal and mechanical stability, is very attractive for (integrated) optical applications. Examples for application of the materials for microoptics as well as for optical back-planes generated by large-area processing will be given.

Ultrafast laser pulses for medical applications

Ultrafast lasers have become a promising tool for micromachining and extremely precise ablation of all kinds of materials. Due to the low energy threshold, thermal and mechanical side effects are limited to the bu micrometers range. The neglection of side effects enables the use of ultrashort laser pulses in a broad field of medical applications. Moreover, the interaction process based on nonlinear absorption offers the opportunity to process transparent tissue three dimensionally inside the bulk. We demonstrate the feasibility of surgical procedures in different fields of medical interest: in ophthalmology intrastromal cutting and preparing of cornael flaps for refractive surgery in living animals is presented. Besides, the very low mechanical side effects enables the use of fs- laser in otoralyngology to treat ocecular bones. Moreover, the precise cutting quality can be used in fields of cardiovascular surgery for the treatment of arteriosklerosis as well as in dentistry to remove caries from dental hard tissue.

Superprism phenomena in polymeric woodpile structures

An analysis of the optical properties of photonic woodpile structures is presented. We demonstrate large superprism phenomena inside polymeric woodpile structures having a refractive index of less than n=1.6. Due to the low contrast in refractive indices the structures investigated do not possess a complete photonic band gap. Nevertheless, their photonic band structures show strong anisotropy at frequencies slightly above the band gap in the (Γ-X) direction, leading to an extreme sensitivity to the angle and the frequency of the incident light in the propagation direction inside the crystal. Furthermore, if the woodpile structure is arranged in a prism-like shape, the transmitted beam outside the crystal shows a strong sensitivity to the frequency and angle of the incident light.

Incorporation of Quantum Dots into 3D Photonic Crystals for Emission Control

This article demonstrates infiltration and doping as two efficient and flexible methods for incorporation of PbSe quantum dots (QDs) into three-dimensional (3D) photonic crystals. QDs induced photonic band gap shift was observed by the infiltration method. By employing the two-photon polymerisation technique, 3D photonic crystals were fabricated with QDs doped resin. Investigation will be focused on radiation dynamics and emission control of QDs in 3D photonic crystals

High-resolution direct-write femtosecond laser technologies

During the last decade it has been proven that focused femtosecond laser pulses are an ideal tool for micro- and sub-micro-structuring of all kinds of materials. Due to the high intensities that can be achieved in ultrashort pulses they can be applied for machining transparent media within the volume by means of multi-photon absorption. Besides ablative methods, multi-photon absorption can also lead to photo-polymerization of light-sensitive resins, i.e. two-photon polymerization. In this paper we present our latest results on the fabrication of 3D microstructures by means of two-photon polymerization.