Dr. Sonja Unger Profile

Dr. Sonja Unger

at Leibniz-Institut für Photonische Technologien eV

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Author

Publications (38)

Proceedings Article | 16 March 2015

The REPUSIL process and the capability of fluorine doping for the adjustment of optical and thermochemical properties in silica materials

K. Schuster, St. Grimm, A. Kalide, Jan Dellith, M. Leich, A. Schwuchow, S. Unger, A. Langner, G. Schötz, H. Bartelt

Proc. SPIE. 9359, Optical Components and Materials XII

KEYWORDS: Thermography, Refractive index, Silica, Cladding, Glasses, Ions, Doping, Ytterbium, Aluminum, Fluorine

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Proceedings Article | 20 February 2015

Demonstration of >5kW emissions with good beam quality from two different 7:1 all-glass fiber coupler-types

M. Plötner, T. Eschrich, O. de Vries, J. Kobelke, S. Unger, M. Jäger, T. Schreiber, H. Bartelt, R. Eberhardt, A. Tünnermann

Proc. SPIE. 9346, Components and Packaging for Laser Systems

KEYWORDS: Multimode fibers, Step index fibers, Fiber optics, Cladding, Capillaries, Silicon, Single mode fibers, Fiber lasers, Fiber couplers, Precision optics

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SPIE Journal Paper | 3 June 2014

Length distributed measurement of temperature effects in Yb-doped fibers during pumping

Martin Leich, Julia Fiebrandt, Anka Schwuchow, Sylvia Jetschke, Sonja Unger, Matthias Jäger, Manfred Rothhardt, Hartmut Bartelt

OE Vol. 53 Issue 06

KEYWORDS: Optical fibers, Fiber Bragg gratings, Temperature metrology, Ytterbium, Absorption, Ultraviolet radiation, Cerium, Fiber lasers, Optical pumping, Hydrogen

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Proceedings Article | 2 June 2014

In-line Mach-Zehnder interferometer based on a dissimilar-doping dual-core fiber for high sensitivity strain and temperature sensing

H, Martins, J. Bierlich, K. Wondraczek, S. Unger, J. Kobelke, K. Schuster, M. Marques, M. Gonzalez-Herraez, O. Frazão

Proc. SPIE. 9157, 23rd International Conference on Optical Fibre Sensors

KEYWORDS: Refractive index, Mach-Zehnder interferometers, Interferometers, Sensors, Germanium, Single mode fibers, Fiber optics sensors, Temperature sensors, Phosphorus, Temperature metrology

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Proceedings Article | 7 March 2014

Spatially resolved in-core temperature measurement in rare-earth doped fibers during pumping

Julia Fiebrandt, Martin Leich, Sonja Unger, Anka Schwuchow, Matthias Jäger, Manfred Rothhardt, Hartmut Bartelt

Proc. SPIE. 8982, Optical Components and Materials XI

KEYWORDS: Fabrication, Optical fibers, Fiber amplifiers, Near infrared, Fiber Bragg gratings, Fiber lasers, Optical pumping, Cerium, Temperature metrology, Absorption

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Proceedings Article | 7 March 2014

Optical properties of Yb-doped fibers prepared by gas phase doping

F. Lindner, C. Aichele, A. Schwuchwo, M. Leich, A. Scheffel, S. Unger

Proc. SPIE. 8982, Optical Components and Materials XI

KEYWORDS: Optical fibers, Refractive index, Silica, Doping, Fiber lasers, Oxygen, Ytterbium, Aluminum, Deposition processes, Absorption

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Proceedings Article | 7 March 2014

Optimization of laser fibers for high pump light absorption

Jörg Bierlich, Jens Kobelke, Sylvia Jetschke, Stephan Grimm, Sonja Unger, Kay Schuster

Proc. SPIE. 8961, Fiber Lasers XI: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Refractive index, Silica, Signal attenuation, Glasses, Laser applications, Fiber lasers, Refraction, Laser glasses, Absorption

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Proceedings Article | 20 February 2014

Improvement of optical damage in specialty fiber at 266 nm wavelength

T. Tobisch, H. Ohlmeyer, H. Zimmermann, S. Prein, J. Kirchhof, S. Unger, M. Belz, K.-F. Klein

Proc. SPIE. 8938, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XIV

KEYWORDS: Silica, Fiber optics, Ultraviolet radiation, Hydrogen, Laser applications, Lamps, Nd:YAG lasers, Fiber lasers, Pulsed laser operation, Absorption

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Proceedings Article | 11 March 2013

Optical properties of cerium-codoped high power laser fibers

S. Unger, A. Schwuchow, S. Jetschke, S. Grimm, A. Scheffel, J. Kirchhof

Proc. SPIE. 8621, Optical Components and Materials X

KEYWORDS: Optical fibers, Refractive index, Ultraviolet radiation, Luminescence, Hydrogen, Doping, Ytterbium, Aluminum, Cerium, Absorption

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Proceedings Article | 31 August 2011

160W single-mode single-frequency Yb-doped fiber laser with fiber Bragg grating inscribed by UV femtosecond exposure and two beam interference

Martin Becker, Sven Brückner, Eric Lindner, Martin Leich, Manfred Rothhardt, Sonja Unger, Hartmut Bartelt

Proc. SPIE. 8007, Photonics North 2011

KEYWORDS: Reflectors, Refractive index, Mirrors, Femtosecond phenomena, Modulation, Fiber Bragg gratings, Ultraviolet radiation, Reflectivity, Interferometry, Fiber lasers

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Proceedings Article | 11 February 2011

Fibers and fiber-optic components for high-power fiber lasers

H. Zimer, M. Kozak, A. Liem, F. Flohrer, F. Doerfel, P. Riedel, S. Linke, R. Horley, F. Ghiringhelli, S. Desmoulins, M. Zervas, J. Kirchhof, S. Unger, S. Jetschke, T. Peschel, T. Schreiber

Proc. SPIE. 7914, Fiber Lasers VIII: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Refractive index, Cladding, Glasses, Single mode fibers, Fiber lasers, Ytterbium, Aluminum, Phosphorus, Absorption

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Proceedings Article | 23 September 2010

Fiber Bragg grating inscription with UV femtosecond exposure and two beam interference for fiber laser applications

Martin Becker, Sven Brückner, Eric Lindner, Manfred Rothhardt, Sonja Unger, Jens Kobelke, Kay Schuster, Hartmut Bartelt

Proc. SPIE. 7750, Photonics North 2010

KEYWORDS: Mirrors, Femtosecond phenomena, Fiber Bragg gratings, Reflection, Ultraviolet radiation, Germanium, Hydrogen, Interferometry, Fiber lasers, Femtosecond fiber lasers

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Proceedings Article | 18 May 2010

Thermal stress anomaly in rare-earth-doped fiber materials for high-power fiber lasers codoped with aluminum and phosphorus

F. Just, S. Unger, J. Kirchhof, V. Reichel, H. Bartelt

Proc. SPIE. 7721, Solid State Lasers and Amplifiers IV, and High-Power Lasers

KEYWORDS: Optical fibers, Superposition, Refractive index, Silica, Cladding, Glasses, Doping, Ytterbium, Aluminum, Phosphorus

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Proceedings Article | 18 May 2010

Thin-disk-laser-pumped ytterbium-doped fiber laser with an output power in the kW range

A. Popp, A. Voss, Th. Graf, S. Unger, J. Kirchhof, H. Bartelt

Proc. SPIE. 7721, Solid State Lasers and Amplifiers IV, and High-Power Lasers

KEYWORDS: Laser sources, Mirrors, Cladding, Ions, Coating, Fiber lasers, Optical simulations, Active optics, Disk lasers, Absorption

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Proceedings Article | 26 February 2010

The influence of Yb2+ ions on optical properties and power stability of ytterbium-doped laser fibers

J. Kirchhof, S. Unger, A. Schwuchow, S. Jetschke, V. Reichel, M. Leich, A. Scheffel

Proc. SPIE. 7598, Optical Components and Materials VII

KEYWORDS: Optical fibers, Silica, Glasses, Ultraviolet radiation, Luminescence, Ions, Doping, Ytterbium, Aluminum, Absorption

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Proceedings Article | 17 February 2010

Temperature dependence of photodarkening kinetics

M. Leich, S. Jetschke, S. Unger, J. Kirchhof

Proc. SPIE. 7580, Fiber Lasers VII: Technology, Systems, and Applications

KEYWORDS: Glasses, Annealing, Fiber lasers, Time metrology, Ytterbium, Thermal effects, Color centers, Thermal modeling, Temperature metrology, Absorption

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Proceedings Article | 5 August 2009

Fiber Bragg grating inscription with DUV femtosecond exposure and two beam interference

Martin Becker, Joachim Bergmann, Sven Brückner, Eric Lindner, Manfred Rothhardt, Kay Schuster, Jens Kobelke, Sonja Unger, Hartmut Bartelt, Luis Fernandes, Paulo V. S. Marques

Proc. SPIE. 7386, Photonics North 2009

KEYWORDS: Refractive index, Mirrors, Femtosecond phenomena, Silica, Fiber Bragg gratings, Interferometers, Glasses, Germanium, Fiber lasers, Absorption

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Fiber Bragg gratings (FBGs) are today fundamental components in fiber optics. They can be used as sensors, in signal processing, e.g. telecom applications, as wavelength stabilizers in fiber lasers or in dispersion compensators. However, there are applications where the demand for fiber Bragg gratings is not compatible with standard photosensitivity techniques like germanium doping or hydrogen loading. Examples are their use as laser-mirrors in spliceless all fiber fiber-laser solutions or the fiber Bragg grating inscription in suspended core all silica fibers for evanescent field sensing. Fiber Bragg grating inscription with femtosecond-laser exposure is a challenging new method to realize grating structures for waveguides made of materials which do not provide UV-photosensitivity. Especially fs-IR-inscription has been demonstrated for Bragg grating inscription in a variety of material systems such as boron-silica glass, sapphire and pure silica glass. The feasibility of the phase mask FBG inscription technique with DUV femtosecond lasers was also shown, which allows grating inscription even in pure silica microstructured fibers. The phase mask inscription method requires that the fiber will be placed directly behind the phase mask. While the laser beam should be focused onto the fiber to support nonlinear material interaction, this inscription method also leads to phase mask degradations, presumably due to non-bridging oxygen holes (NBOH). Our solution to avoid the mask degradation is to increase the space between fiber and phase mask by using a Talbot-interferometer. Another advantage is the wavelength versatility of this inscription setup. Due to the short temporal coherence length of the femtosecond pulses, the angular alignment variability of the interferometer mirrors is limited and restrictions concerning the wavelength versatility of the interferometer arise. Grating arrays in pure silica suspended core fibers are demonstrated as an example for the versatility of the inscription arrangement.

Proceedings Article | 19 February 2009

Yb-doped silica-based laser fibers: correlation of photodarkening kinetics and related optical properties with the glass composition

J. Kirchhof, S. Unger, S. Jetschke, A. Schwuchow, M. Leich, V. Reichel

Proc. SPIE. 7195, Fiber Lasers VI: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Optical properties, Glasses, Ultraviolet radiation, Luminescence, Ions, Oxygen, Ytterbium, Aluminum, Absorption

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Proceedings Article | 19 February 2009

Comparison of silica-based materials and fibers in side- and end-pumped fiber lasers

Andreas Langner, Gerhard Schötz, Mario Such, Volker Reichel, Stephan Grimm, Martin Leich, Sonja Unger, Johannes Kirchhof, Björn Wedel, Volker Krause, Georg Rehmann

Proc. SPIE. 7195, Fiber Lasers VI: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Silica, Cladding, Signal attenuation, Laser applications, Laser development, Doping, Fiber lasers, Semiconductor lasers, Phosphorus

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Proceedings Article | 19 February 2009

Characterization of photodarkening processes in Yb doped fibers

S. Jetschke, U. Röpke, S. Unger, J. Kirchhof

Proc. SPIE. 7195, Fiber Lasers VI: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Switching, Cladding, Ions, Manufacturing, Fiber lasers, Time metrology, Ytterbium, Transmittance, Color centers

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Proceedings Article | 7 February 2009

Influence of aluminum-phosphorus codoping on optical properties of ytterbium-doped laser fibers

S. Unger, A. Schwuchow, S. Jetschke, V. Reichel, M. Leich, A. Scheffel, J. Kirchhof

Proc. SPIE. 7212, Optical Components and Materials VI

KEYWORDS: Optical fibers, Refractive index, Optical properties, Glasses, Luminescence, Fiber lasers, Ytterbium, Aluminum, Phosphorus, Absorption

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Proceedings Article | 22 February 2008

Photodarkening in Yb-doped silica fibers: influence of the atmosphere during preform collapsing

S. Jetschke, S. Unger, A. Schwuchow, M. Leich, V. Reichel, J. Kirchhof

Proc. SPIE. 6873, Fiber Lasers V: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Near infrared, Cladding, Glasses, Luminescence, Ions, Fiber lasers, Oxygen, Ytterbium, Absorption

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Proceedings Article | 5 February 2008

Optical properties of Yb-doped laser fibers in dependence on codopants and preparation conditions

S. Unger, A. Schwuchow, S. Jetschke, V. Reichel, A. Scheffel, J. Kirchhof

Proc. SPIE. 6890, Optical Components and Materials V

KEYWORDS: Optical fibers, Glasses, Ultraviolet radiation, Luminescence, Ions, Fiber lasers, Ytterbium, Aluminum, Phosphorus, Absorption

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Proceedings Article | 22 February 2007

Preparation of large-mode-area laser fibers with microstructured cores

Jens Kobelke, Kay Schuster, Sonja Unger, Volker Reichel, Anka Schwuchow, Klaus Mörl, Johannes Kirchhof, Martin Leich

Proc. SPIE. 6453, Fiber Lasers IV: Technology, Systems, and Applications

KEYWORDS: Optical fibers, Refractive index, Silica, Cladding, Signal attenuation, Fiber lasers, Ytterbium, Phosphorus, Fluorine, Absorption

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Proceedings Article | 20 February 2007

Codoped materials for high power fiber lasers: diffusion behaviour and optical properties

Sonja Unger, Anka Schwuchow, Jan Dellith, Johannes Kirchhof

Proc. SPIE. 6469, Optical Components and Materials IV

KEYWORDS: Refractive index, Silica, Optical properties, Signal attenuation, Glasses, Diffusion, Doping, Aluminum, Phosphorus, Aluminium phosphide

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Proceedings Article | 23 September 2005

Materials and technologies for microstructured high power laser fibers

J. Kirchhof, S. Unger, J. Kobelke, K. Schuster, K. Mörl, S. Jetschke, A. Schwuchow

Proc. SPIE. 5951, Optical Fibers: Technology

KEYWORDS: Optical fibers, Refractive index, Cladding, Doping, Fiber lasers, Solids, Ytterbium, Aluminum, Boron, Absorption

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SPIE Journal Paper | 1 June 2005

High-reflectivity draw-tower fiber Bragg gratings—arrays and single gratings of type II

Christoph Chojetzki, Manfred Rothhardt, J. Ommer, Sonja Unger, Kay Schuster, Hans-Rainer Mueller

OE Vol. 44 Issue 06

KEYWORDS: Reflectivity, Fiber Bragg gratings, Excimer lasers, Manufacturing, Sensors, Pulsed laser operation, Interferometers, Single mode fibers, Optical components, Ultraviolet radiation

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Proceedings Article | 22 April 2005

Nd:Yb-codoped silica fibers for high power fiber lasers: fluorescence and laser properties

Sylvia Jetschke, Volker Reichel, Klaus Moerl, Sonja Unger, Ulrich Roepke, Hans-Rainer Mueller

Proc. SPIE. 5709, Fiber Lasers II: Technology, Systems, and Applications

KEYWORDS: Optical fibers, High power lasers, Luminescence, Energy transfer, Ions, Fiber lasers, Ytterbium, High power fiber lasers, Neodymium, Absorption

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Proceedings Article | 4 April 2005

Dopant interactions in high-power laser fibers

Johannes Kirchhof, Sonja Unger, Anka Schwuchow, Sylvia Jetschke, Bruno Knappe

Proc. SPIE. 5723, Optical Components and Materials II

KEYWORDS: Optical fibers, Refractive index, Silica, Glasses, Luminescence, Germanium, Ytterbium, Aluminum, Neodymium, Absorption

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Proceedings Article | 23 March 2005

Fiber-laser power scaling beyond the 1-kilowatt level by Nd:Yb co-doping

Volker Reichel, Klaus Moerl, Sonja Unger, Sylvia Jetschke, Hans-Rainer Mueller, Johannes Kirchhof, Thomas Sandrock, Alexander Harschack, Andreas Liem, Jens Limpert, Holger Zellmer, Andreas Tuennermann

Proc. SPIE. 5777, XV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers

KEYWORDS: Optical fibers, Silica, Energy transfer, Materials processing, Laser marking, Fiber lasers, Semiconductor lasers, Ytterbium, Neodymium, Absorption

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Proceedings Article | 14 June 2004

Spatial distribution effects and laser efficiency in Er/Yb-doped fibers

Johannes Kirchhof, Sonja Unger, Anka Schwuchow, Sylvia Jetschke, Bruno Knappe

Proc. SPIE. 5350, Optical Components and Materials

KEYWORDS: Optical fibers, Glasses, Luminescence, Diffusion, Doping, Fiber lasers, Ytterbium, Aluminum, Erbium, Phosphorus

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Proceedings Article | 7 June 2004

Air-clad large-mode-area photonic crystal fibers: power scaling concepts up to the multi-kW range

Andreas Liem, Jens Limpert, Thomas Schreiber, Stefan Nolte, Holger Zellmer, Andreas Tuennermann, Jes Broeng, Guillaume Vienne, Anders Petersson, Christian Jakobsen, Thomas Peschel, Volker Guyenot, Volker Reichel, Sonja Unger

Proc. SPIE. 5335, Fiber Lasers: Technology, Systems, and Applications

KEYWORDS: Continuous wave operation, Photonic crystal fibers, Silica, Cladding, Coating, Fiber lasers, Ytterbium, Finite element methods, Bridges, Absorption

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Proceedings Article | 3 July 2003

Applications of pumped-multiplexed Yb-doped fiber lasers

Volker Reichel, Sonja Unger, Sven Bruckner, Klaus Morl, Hans-Rainer Muller, Johannes Kirchhof, Thomas Sandrock, Alexander Harschack

Proc. SPIE. 4974, Advances in Fiber Lasers

KEYWORDS: Refractive index, Mirrors, Silica, Glasses, Silicon, Fiber lasers, Semiconductor lasers, Ytterbium, Dielectric mirrors, Absorption

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Proceedings Article | 1 July 2003

Fiber lasers: materials, structures and technologies

Johannes Kirchhof, Sonja Unger, Anka Schwuchow

Proc. SPIE. 4957, Optical Fibers and Sensors for Medical Applications III

KEYWORDS: Silica, Cladding, Glasses, Luminescence, Diffusion, Doping, Fiber lasers, Ytterbium, Aluminum, Neodymium

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Proceedings Article | 26 March 2002

Transmission behavior of silica core: fluorine-doped cladding fibers in the visible and ultraviolet region

Sonja Unger, Johannes Kirchhof, Siegmund Schroeter, Anka Schwuchow, Holger Frost

Proc. SPIE. 4616, Optical Fibers and Sensors for Medical Applications II

KEYWORDS: Optical fibers, Silica, Ultraviolet radiation, Germanium, Diffusion, Doping, Oxygen, Aluminum, Fluorine, Absorption

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Proceedings Article | 19 October 2001

High-power stability of optical fibers for the visible wavelength region

Johannes Kirchhof, Sonja Unger, Siegmund Schroeter, Anka Schwuchow, Holger Frost, Christhard Deter

Proc. SPIE. 4579, Optical Fiber and Planar Waveguide Technology

KEYWORDS: Optical fibers, Silica, Cladding, Ultraviolet radiation, Hydrogen, Diffusion, Doping, Chlorine, Fluorine, Absorption

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Proceedings Article | 3 April 2000

8-W highly efficient Yb-doped fiber laser

Volker Reichel, Sonja Unger, Volker Hagemann, Hans-Rainer Mueller, Mario Auerbach

Proc. SPIE. 3889, Advanced High-Power Lasers

KEYWORDS: Optical fibers, Mirrors, Resonators, Silica, Fiber Bragg gratings, Fiber lasers, Laser resonators, Ytterbium, Micromirrors, Precision optics

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In this paper a very compact device of a very efficient high- power fiber-laser based on a specially designed Ytterbium (Yb)-doped double-clad D-Shape silica fiber with an output power of more than 8 watts will be described. The development, preparation and characterization of rare-earth doped double- clad optical fibers based on silica for the application in high-power fiber-lasers were done at the Optics Division of the Institute for Physical High-Technology e.V. Jena (IPHT) in the last few years. The doping with Ytterbium as the laseractive component was one of the most important questions which were investigated. Many samples had to be made for the optimum concentration of Yb, the optimum codoping and geometry, respectively. As a result of these experiments we realized a double-clad fiber with D-shape geometry of the pump-core. This D-shape resulted from ray-tracing calculations performed at the Lasercentre Hannover e.V. (LZH) as an optimal solution for the high conversion efficiency of the pump-power. Considering these numerical results, such fibers were realized at IPHT by drawing a sidepolished preform by preserving the cross section of the preform. After some basic investigations on the optimum wavelength for the pump-light and the resonator length, respectively, a compact device with a launched pump- power of approx. 13 W and an output-power of more than 8 watts was developed and realized. The maximum output-power was only limited by the pump-power available at our laboratory at the chosen wavelength. Main advantages of the setup are the short length of the laseractive fiber (less than 10 m), the high efficiency (greater than 60%) and the compactness of the device. Additionally, the diameter of the pump-core was reduced to 125 micrometer. These kinds of fibers were tested with a specially designed pump-source of the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena. The first result with a double-clad Yb-doped fiber of only 4 meter length was a fiber-laser with an output-power of about 4 Watts. Last but not least, some basic experiments with Fiber-Bragg-Gratings (FBG) as one of the resonator mirrors were done. A fiber-laser with a FBG for the laser-wavelength had an output-power of about 700 mW with a FWHM of about 0.1 nm.

Proceedings Article | 27 May 1998

High-power single-mode Nd-doped fiber laser

Volker Reichel, Sonja Unger, Hans-Rainer Mueller, Holger Zellmer

Proc. SPIE. 3265, Solid State Lasers VII

KEYWORDS: Multimode fibers, Optical fibers, Refractive index, Mirrors, Silica, Signal attenuation, Luminescence, Germanium, Fiber lasers, Neodymium

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