Supported by the Free State of Thuringia with funds from the European Social Fund.

The overall project “Fiber Technology for Researching the Power Limits of Laser Fibers” aims to investigate limiting effects of fiber power scaling for laser systems with excellent beam quality through fundamental investigations. The basis for this is the cooperation between the Leibniz IPHT Jena and the Fraunhofer IOF Jena, which has been proven over many years and whose competencies complement each other excellently in the subject matter applied for here. The synergy of the two subprojects will make it possible to effectively advance this research.

One focus of Leibniz IPHT’s research activities will be technological investigations into the realization of thulium- and holmium-doped laser fibers using gas phase doping to open up the spectral range around 2 µm. Gas phase doping is the method of choice for power scaling (cw & pulse power) using large fiber cores (LMA concept) with extremely homogeneous dopant distribution. In addition, concentration ranges of codotands (Al) can be developed, which are decisive for a high energy efficiency of powerful Tm-based fiber lasers (cross-relaxation effects). 

Furthermore, coding with Ce is also to be done via the gas phase in order to suppress photo-darkening (PD) effects in Yb and Tm- doped fibers, which are regarded as a major cause of mode instabilities (MI). From this connection (PD & MI) arises, among other things, the necessity and opportunity for close cooperation with the research group of the IOF in order to gain new scientific knowledge on performance scaling.

Another focus of the research group is the investigation of new photosensitive fibers for the fiber-integrated realization of resonator mirrors.

The shift of the wavelength of fiber lasers into the eye-safe range by 2 µm opens up new fields for applications in medical technology or material processing (e.g. polymer surfaces) in addition to the increase of the mode instability threshold to be investigated. However, this requires a wavelength scalability (tunability) for addressing specific wavelengths around 2 µm. The concept of step-chirped gratings as variably addressable resonators, which has already been successfully applied in Yb-doped fiber lasers, is to be researched here and transferred to larger wavelengths for power scaling.

The joint activities of the research groups also serve to support the work on setting up the fiber technology center on the Beutenberg campus.

Funding code: 2015 FGR 0108