Laser Components

Current research focus

• QUEST
  A cornerstone of topical research in the Cluster of Excellence “Quantum Engineering and Space Time Research”, QUEST, is the research area “Enabling Technologies”, where the technological basement of the other three areas is subject of research. Within QUEST the technology area was established and consolidated by strategic investments and a new professorship in Applied Physics.

  On the novel optics side the QUEST project Advanced Optical Materials was backed up with a new home-built coating facility (see figure 1) implementing a novel phase separated deposition process, which aims at lowest optical losses and reduced defect densities in the coatings. Investigations in the control of deposition processes resulted in a comprehensive simulation of layer thickness deviations and accuracy in the atomic scale for certain layer designs. A variety of ternary oxide material combinations were studied before the back-ground of extensive models and improved beyond the former quality level in losses and power handling capability.

  The main aspect of the optimisation is based on a deeper understanding of the coating process and the film formation, but also the generation of coating conditions for lowest contaminations. Applying the novel plasma guiding approach, the spatial separation of material generation and deposition process is achieved. In this concept, the coating material is guided by a coaxial magnetic field and the direct line of view is masked by using a bent guiding coil. Consequently, only ionised deposition material of atomic scale can pass the guiding system and macro-particles are filtered. Applying this approach, coatings with equal particle density compared to the substrates were manufactured. For example, the optical scatter maps of the pure substrate and the dielectric stack including 73 layers are presented in figure 2. Obviously, a marginal increase in particle density was observed. A major parameter for the nucleation of the high quality films is the control of the coating material with respect to the kinematic properties as well as the specific composition of the adatoms. The concept of the phase separating IBS process allows controlling the species during the deposition process by varying the magnetic field strength of the guiding system. The manipulation of the energy distribution and the filtering of the material enable the possibility for novel concepts. Figure 3 displays the simulation of layer formation at different energies.

• PhoenixD Task Group M3 Surface Polishing, Coatings and Optical Elements
  Today, in most innovative photonic systems, where a complex combination of many functions is commonly required, the corresponding optical designs consist of several individual components tediously assembled in serial processes. Future generations of optical systems realized in the Cluster of Excellence PhoenixD will be based on fewer or even just a single optical element which integrates the necessary functions in a much more compact and resource-efficient form. The research work of Task group M3 is dedicated to the production and assembly of optical components to functional units. Major activities of the group Laser Components and Fibres within task group M3 are focused on the design and production of optical filters with small dimension for direct integration in photonic platforms. For this purpose, a special production chain is developed to design, coat, separate, and tailor optical coatings on substrates with a thickness down to a few microns. These subminiature optical components will be integrated with specific assembly techniques in platforms with additional optical devices including laser diodes, waveguides, detectors or diffractive components to form small-scale devices with complex functions. Further emphasis will be also imposed on the development of switchable filter system on the basis of new materials with specific electro-optical, thermal or electrostrictive properties.  

• PhoenixD Task Group S2: Optical Materials
  Within the PhoenixD Task Group S2: Optical Materials the group Laser Components and Fibres concentrates on the simulation of material structures and the growth of optical coatings under various deposition conditions. The corresponding Monte Carlo and Molecular Dynamics computer algorithms are developed and optimized in respect to specific challenges defined by the PhoenixD targets. In addition, the optical properties like the refractive indices and the mechanical properties of the modeled structures are calculated for example by using electronic density functional theory (DFT) techniques. When the average dielectric permittivity and the molecular structure of a possibly complex composite material have been determined, its optical functioning can be derived from the solution of Maxwell’s equations. Different methods can be used for the numerical solution depending on the system complexity. One of the most powerful instruments employed in the group for the solution of Maxwell’s equations is the finite difference time domain (FDTD) method.

• COMET: Center for Optical Coatings and Metrology

  Joined expertise for new challenges

  Thin-film technology is an integral part of optics and photonics. However, due to the continuous technical advances, the demands on optical components for both, research and development as well as industrial applications keep increasing. Here, for example mirrors or filters with properties, such as high stability, minimal absorption and negligible scattering losses are needed. To meet these challenges, it is a crucial advantage to combine the expertise and the existing infrastructure of several research institutions in a joint-use partnership.

  International leadership in thin-film research

  Already now, the two departments of the Laser Zentrum Hannover e.V. and the Fraunhofer Institute for Applied Optics and Precision Engineering are international pioneers. In modern thin-film research, their expertise sets them apart from the competition and represents a unique selling point. Concerning the Laser Zentrum Hannover e.V., ion beam sputtering (IBS) processes and characterization measurements according to ISO standards are the key topics where the institute contributes special know-how and experience. In addition, the IOF has special knowledge about optical functional layers and nanostructures on plastics as well as high-quality coatings for the DUV to EUV range. Through the cooperation sought in the COMET partnership, the two institutes complement each other. Thus, they cover the entire scientific and technological field of optical thin-film technology in a unique way. This includes both the physical fundamentals and knowledge about available materials but also the various existing manufacturing processes and characterisation methods.

  Solutions for the next generation

  "By now, these extremely high demands and the resulting questions cannot be addressed by a single research provider anymore", summarizes Prof. Dr. Andreas Tünnermann at the opening. "The economy and science expect us to join competencies. This is the only way to find solutions for the next generation."

  Within COMET, the Laser Zentrum Hannover e.V. and  Fraunhofer Institute for Applied Optics and Precision Engineering have created an optimum cooperation to be able to fulfil even complicated and most difficult demands on the optical components of tomorrow.

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