The large ratio of surface to active volume of such a fiber ensures excellent heat dissipation. Furthermore the beam quality is defined by the refractive index profile of the active core and is therefore independent of the pump power. Fiber lasers and amplifiers offer a very high single-pass gain and therefore low laser thresholds and efficient diode-pumped operation. Using advanced fiber designs, in continuous-wave (cw) operation output powers exceeding the 10 kW-level with diffraction-limited beam quality have been demonstrated. In the pulsed regime average powers in the order of several hundred Watt even for few cycle pulses based on fiber lasers have been reported.
However, power and energy scaling of cw and pulsed single-mode fiber lasers and amplifiers are restricted due to nonlinear pulse distortions, which are enhanced by the large product of light intensity and interaction length inside the fiber core. In addition, transverse mode instabilities are observed, which degrade the beam quality emitted by high-power fiber laser systems once a certain average power threshold has been reached. Most recently, strategies have been developed to mitigate or even, ideally, to overcome these limitations – enabling a further power scaling of fiber lasers and amplifiers. These strategies are based on advanced large mode area fiber designs and modern coherently coupled multi-channel laser and amplifier architectures.
In this contribution the state of the art of science and technology in fiber lasers and amplifiers is reviewed. The prospects for future developments using advanced fiber designs in combination with modern laser and amplifier architectures are discussed.
Andreas Tünnermann was born in Ahnsen, Germany, on June 10th, 1963. He received the diploma and Ph.D. degrees in physics from the University of Hannover in 1988 and 1992, respectively. His Ph.D. work was focused on nonlinear processes with emphasis on the interaction of high intensity laser sources with matter for the generation of short wavelengths lasers. In 1997 he received the habilitation and venia legendi in experimental physics for his work on ultrastable light sources for interferometric gravitational wave detectors. He was head of the department of development at the Laser Zentrum Hannover from 1992 to 1997. In the beginning of 1998 he joined the Friedrich-Schiller-University in Jena, Germany as a Professor and Director of the Institute of Applied Physics. 2001 he launched the company Guided Color Technologies GmbH. In 2003 he became the Director of the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena.
Andreas Tünnermann is currently leading one of the most creative and productive research groups in modern optics and photonics world-wide. Research topics are the design and manufacturing of novel passive and active photonic devices and its application for generation, amplification, steering and switching of light – with a strong foundation in laser physics. Especially his work on high power continuous and pulsed fiber lasers operating in the visible and near infrared spectral range is highly appreciated by the laser community. Outstanding developments in photonic crystal fiber design performed in his laboratories made it possible to overcome restrictions due to nonlinear pulse distortions in the amplification fiber and revealed the full potential of rare-earth-doped fibers as a power-scalable solid-state laser concept even in the ultrashort pulse regime.
The blend of experience and knowledge manifests itself in a work that has attracted and continues to attract considerable attention as proven by more than 500 peer-reviewed publications in renown international journals (e.g. Nature Physics, Nature Photonics, Physical Review Letters, Optics Letters, Applied Optics, Applied Physics A+B and Optics Express), and more than 150 invited talks at most important national and international conferences, including plenary talks and tutorials.
Andreas Tünnermann has been distinguished with several prizes and awards along his professional career. He received the most important German award in science and technology, provided by the German Research Foundation (DFG), the Gottfried Wilhelm Leibniz Prize. Most recently, he has been awarded with the ERC Advanced Grant of the European Community.