Jens Limpert

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2017, 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC).

Surface-emitted THz generation using a compact ultrashort pulse fiber amplifier at 1060 nm

Jens Limpert, Andreas Tünnermann, Gabor Matthäus, 2006 .

Energetic sub-2-cycle laser with 216 W average power.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2016, Optics letters.

On the study of pulse evolution in ultra-short pulse mode-locked fiber lasers by numerical simulations.

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2007, Optics express.

High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber.

Jens Limpert, Andreas Tünnermann, Alexander Hartung, 2011, Optics express.

Basic considerations on coherent combining of ultrashort laser pulses.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2011, Optics express.

High stability soliton frequency-shifting mechanisms for laser synchronization applications

Jens Limpert, Andreas Tünnermann, Alexander M. Heidt, 2012 .

Reduction of timing jitter in passively Q-switched microchip lasers using self-injection seeding.

Jens Limpert, Andreas Tünnermann, Alexander Steinmetz, 2010, Optics letters.

1 kW narrow-linewidth fiber amplifier for spectral beam combining

Jens Limpert, Andreas Tünnermann, Ramona Eberhardt, 2008 .

Experimental and numerical study of pulse dynamics in positive net-cavity dispersion mode-locked Yb-doped all-fiber lasers

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2008 .

Spectral beam combining of fiber lasers

Jens Limpert, Andreas Tünnermann, Ramona Eberhardt, 2006 .

All-fiber laser source for CARS microscopy based on fiber optical parametric frequency conversion.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2012, Optics express.

High-power thermally guiding index-antiguiding-core fibers.

Cesar Jauregui, Hans-Jürgen Otto, Fabian Stutzki, 2013, Optics Letters.

High average power femtosecond fiber CPA system

Jens Limpert, Andreas Tünnermann, Stefan Nolte, 2002 .

2 kW average power from a pulsed Yb-doped rod-type fiber amplifier.

Cesar Jauregui, Hans-Jürgen Otto, Fabian Stutzki, 2014, Optics letters.

High-power femtosecond Yb-doped fiber amplifier.

Jens Limpert, J. Limpert, A. Tünnermann, 2002, Optics express.

Electro-optically controlled divided-pulse amplification.

Jens Limpert, Andreas Tünnermann, Marco Kienel, 2017, Optics express.

Modal energy transfer by thermally induced refractive index gratings in Yb-doped fibers

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2018, Light: Science & Applications.

Spectral beam combining of Yb-doped fiber lasers with high efficiency

Jens Limpert, Andreas Tünnermann, Fabian Röser, 2007 .

Passively Mode-Locked Single-Polarization Microstructure Fiber Laser

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2008 .

Yb-doped Large Pitch Fiber with 105 µm mode field diameter

Cesar Jauregui, Tino Eidam, Fabian Stutzki, 2011, 2011 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference.

BBO-sapphire sandwich structure for frequency conversion of high power lasers

Jens Limpert, Andreas Tünnermann, Ramona Eberhardt, 2014 .

Scalability of components for kW-level average power few-cycle lasers.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2016, Applied optics.

Watt-scale super-octave mid-infrared intrapulse difference frequency generation

Cesar Jauregui, Fabian Stutzki, Jens Limpert, 2018, Light: Science & Applications.

Theoretical analysis of the gain bandwidth for noncollinear parametric amplification of ultrafast pulses

Jens Limpert, Andreas Tünnermann, D. C. Hanna, 2007 .

High-order harmonic generation at a megahertz-level repetition rate directly driven by an ytterbium-doped-fiber chirped-pulse amplification system.

Jens Limpert, Yoann Zaouter, Eric Cormier, 2009, Optics letters.

Linearly polarized ytterbium fiber laser based on intracore femtosecond-written fiber Bragg gratings.

Jens Limpert, Andreas Tünnermann, Stefan Nolte, 2007, Optics letters.

Thermal effects in high average power optical parametric amplifiers.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2013, Optics letters.

Octave-spanning OPCPA system delivering CEP-stable few-cycle pulses and 22 W of average power at 1 MHz repetition rate.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2012, Optics express.

Extraction of enhanced, ultrashort laser pulses from a passive 10-MHz stack-and-dump cavity

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2016, Applied physics. B, Lasers and optics.

1 kW 1 mJ eight-channel ultrafast fiber laser.

Jens Limpert, Andreas Tünnermann, Marco Kienel, 2016, Optics letters.

Real-time characterisation of modal content in monolithic few-mode fibre lasers

Cesar Jauregui, Fabian Stutzki, Jens Limpert, 2011 .

Fiber-based optical parametric oscillator for high resolution coherent anti-Stokes Raman scattering (CARS) microscopy.

Jens Limpert, Andreas Tünnermann, Jürgen Popp, 2014, Optics express.

High brightness spectral beam combining to 8.2 kW

Jens Limpert, Andreas Tünnermann, Ramona Eberhardt, 2011 .

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems.

Jens Limpert, Andreas Tünnermann, Marco Jupé, 2003, Applied optics.

High energy ultrashort pulses via hollow fiber compression of a fiber chirped pulse amplification system.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2009, Optics express.

Fiber based polarization filter for radially and azimuthally polarized light.

Cesar Jauregui, Fabian Stutzki, Jens Limpert, 2011, Optics express.

16 Channel Coherently-Combined Ultrafast Fiber Laser

Jens Limpert, Andreas Tünnermann, Arno Klenke, 2017 .

Long period gratings written in large-mode area photonic crystal fiber

Florian Jansen, Jens Limpert, Andreas Tünnermann, 2008 .

Sequential phase locking scheme for a filled aperture intensity coherent combination of beam arrays.

Jens Limpert, Andreas Tünnermann, Arno Klenke, 2018, Optics express.

Power scaling of high-power fiber lasers and amplifiers

Jens Limpert, Andreas Tünnermann, Volker Guyenot, 2005 .

High Repetition Rate Ultrashort Pulse Micromachining with Fiber Lasers

Jens Limpert, Andreas Tünnermann, Stefan Nolte, 2011 .

Fiber CPA System delivering 2.2 mJ, sub 500 fs pulses with 3.8 GW Peak Power

Tino Eidam, Fabian Stutzki, Florian Jansen, 2011 .

Avoided crossings in photonic crystal fibers.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2011, Optics express.

Decrease of pulse-contrast in nonlinear chirped-pulse amplification systems due to high-frequency spectral phase ripples.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2008, Optics express.

152 W average power Tm-doped fiber CPA system.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2014, Optics letters.

Petawatt and exawatt class lasers worldwide

Jens Limpert, Jingui Ma, Liejia Qian, 2019, High Power Laser Science and Engineering.

High average and peak power femtosecond large-pitch photonic-crystal-fiber laser.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2011, Optics letters.

High-average-power 2 μm few-cycle optical parametric chirped pulse amplifier at 100 kHz repetition rate.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2015, Optics letters.

A concept for multiterawatt fibre lasers based on coherent pulse stacking in passive cavities

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2014, Light: Science & Applications.

Analysis of passively combined divided-pulse amplification as an energy-scaling concept.

Cesar Jauregui, Tino Eidam, Jens Limpert, 2013, Optics express.

Scaling ultrashort laser pulse induced glass modifications for cleaving applications.

Jens Limpert, Stefan Nolte, Michael Müller, 2018, Applied optics.

Femtosecond fiber CPA system emitting 830 W average output power.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2010, Optics letters.

µJ-Level All-Polarization-Maintaining Femtosecond Fiber Laser

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2006 .

Megawatt peak power level fiber laser system based on compression in air-guiding photonic bandgap fiber

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2004 .

Fiber based chirped pulse amplification system with 22 W average power [for laser plasma EUV generation]

Jens Limpert, Andreas Tünnermann, Georg Korn, 2001, CLEO 2001.

High average power supercontinuum generation in photonic crystal fibers

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2003 .

26 mJ, 130 W Q-switched fiber-laser system with near-diffraction-limited beam quality.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2012, Optics letters.

Generation of coherent broadband high photon flux continua in the XUV with a sub-two-cycle fiber laser.

Jens Limpert, Jan Rothhardt, Wilhelm Eschen, 2020, Optics express.

Control of nonlinear spectral phase induced by ultra-broadband optical parametric amplification.

Jens Limpert, Andreas Tünnermann, Jake Bromage, 2012, Optics letters.

Approaching microjoule-level pulse energy with mode-locked femtosecond fiber lasers.

Jens Limpert, Andreas Tünnermann, Bülend Ortaç, 2009, Optics letters.

Fiber‐based light sources for biomedical applications of coherent anti‐Stokes Raman scattering microscopy

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2015 .

Relative amplitude noise transfer function of an Yb3+-doped fiber amplifier chain.

Cesar Jauregui, Jens Limpert, Thomas Gottschall, 2019, Optics express.

Fiber chirped-pulse amplification system emitting 3.8 GW peak power.

Cesar Jauregui, Tino Eidam, Fabian Stutzki, 2011, Optics express.

Tm-based fiber-laser system with more than 200 MW peak power.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2015, Optics letters.

Coherent Beam Combination of Ultrafast Fiber Lasers

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2018, IEEE Journal of Selected Topics in Quantum Electronics.

Preferential gain photonic-crystal fiber for mode stabilization at high average powers.

Cesar Jauregui, Tino Eidam, Fabian Stutzki, 2011, Optics express.

Phase-shift evolution of the thermally-induced refractive index grating in high-power fiber laser systems induced by pump-power variations.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2018, Optics express.

66 W average power from a microjoule-class sub-100 fs fiber oscillator.

Jens Limpert, Andreas Tünnermann, Ammar Hideur, 2012, Optics letters.

2 MHz repetition rate, 200 ps pulse duration from a monolithic, passively Q-switched microchip laser

Jens Limpert, Andreas Tünnermann, Alexander Steinmetz, 2009 .

Generation of high quality, 1.3 cycle pulses by active phase control of an octave spanning supercontinuum.

Jens Limpert, Andreas Tünnermann, Alexander Hartung, 2011, Optics express.

12 mJ kW-class ultrafast fiber laser system using multidimensional coherent pulse addition.

Jens Limpert, Andreas Tünnermann, Marco Kienel, 2016, Optics letters.

Enhancing the macroscopic yield of narrow-band high-order harmonic generation by Fano resonances.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2014, Physical review letters.

150 W Nd/Yb codoped fiber laser at 1.1 /spl mu/m

Jens Limpert, Andreas Tünnermann, Andreas Liem, 2002, CLEO 2002.

Large-pitch Multicore Fiber for Coherent Combination of Ultrashort Pulses

Tino Eidam, Hans-Jürgen Otto, Fabian Stutzki, 2015, CLEO 2015.

Fiber based optical parametric oscillator for high fidelity coherent anti-stokes Raman (CARS) microscopy

Jens Limpert, Andreas Tünnermann, Jürgen Popp, 2013 .

High power picosecond amplification in a low-nonlinearity single-mode photonic crystal fiber

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2004 .

High-harmonic generation at 250 MHz with photon energies exceeding 100 eV

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2016 .

Controlling mode instabilities by dynamic mode excitation with an acousto-optic deflector.

Cesar Jauregui, Hans-Jürgen Otto, Fabian Stutzki, 2013, Optics express.

Gain Limitations and Consequences for Short Length Fiber Amplifiers

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2008 .

Pre-chirp managed nonlinear amplification in fibers delivering 100 W, 60 fs pulses.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2015, Optics letters.

Coherently combined fiber laser system delivering 120 μJ femtosecond pulses.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2011, Optics letters.

Pump-modulation-induced beam stabilization in high-power fiber laser systems above the mode instability threshold.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2018, Optics express.

High-power efficient generation of visible and mid-infrared radiation exploiting four-wave-mixing in optical fibers.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2012, Optics express.

88 W 0.5 mJ femtosecond laser pulses from two coherently combined fiber amplifiers.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2011, Optics letters.

Self-phase modulation compensated by positive dispersion in chirped-pulse systems.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2009, Optics express.

Advances in laser concepts for multiplex, coherent Raman scattering micro-spectroscopy and imaging

Jens Limpert, Andreas Tünnermann, Jürgen Popp, 2018 .

1 MHz repetition rate hollow fiber pulse compression to sub-100-fs duration at 100 W average power.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2011, Optics letters.

High average power spectral beam combining of four fiber amplifiers to 8.2 kW.

Jens Limpert, Andreas Tünnermann, Ramona Eberhardt, 2011, Optics letters.

Coherent addition of fiber-amplified ultrashort laser pulses.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2010, Optics express.

The renaissance and bright future of fibre lasers

Jens Limpert, Andreas Tünnermann, Stefan Nolte, 2005 .

Erbium fiber laser based on intracore femtosecond-written fiber Bragg grating.

Jens Limpert, Andreas Tünnermann, Ulrike Fuchs, 2006, Optics letters.

Nonlinear compression of Q-switched laser pulses to the realm of ultrashort durations.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2011, Optics Express.

The future is fibre accelerators

Jens Limpert, Gerard Mourou, Toshiki Tajima, 2013, Nature Photonics.

0.5 μJ diode pumped femtosecond laser oscillator at 9 MHz

Jens Limpert, Martin Delaigue, Antoine Courjaud, 2005 .

Physical origin of mode instabilities in high-power fiber laser systems.

Cesar Jauregui, Tino Eidam, Hans-Jürgen Otto, 2012, Optics express.

High-speed modal decomposition of mode instabilities in high-power fiber lasers.

Cesar Jauregui, Hans-Jürgen Otto, Fabian Stutzki, 2011, Optics letters.

53 W average power few-cycle fiber laser system generating soft x rays up to the water window.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2014, Optics letters.

Controlling the influence of SPM in fiber-based chirped-pulse amplification systems by using an actively shaped parabolic spectrum.

Jens Limpert, Andreas Tünnermann, J. Limpert, 2007, Optics express.

Exploring new avenues in high repetition rate table-top coherent extreme ultraviolet sources

Jens Limpert, Andreas Tünnermann, Arno Klenke, 2015, Light: Science & Applications.

Power scaling of a high-repetition-rate enhancement cavity.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2010, Optics letters.

Absorption-limited and phase-matched high harmonic generation in the tight focusing regime

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2014 .

High Repetition Rate Seeding of a Free-Electron Laser at DESY Hamburg

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2010 .

Multidimensional coherent pulse addition of ultrashort laser pulses.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2015, Optics letters.

Circular versus linear polarization in laser-amplifiers with Kerr-nonlinearity.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2009, Optics express.

Observation of soliton molecules with independently evolving phase in a mode-locked fiber laser.

Jens Limpert, Andreas Tünnermann, Rumen Iliew, 2010, Optics letters.

The influence of index-depressions in core-pumped Yb-doped large pitch fibers.

Cesar Jauregui, Hans-Jürgen Otto, Fabian Stutzki, 2010, Optics express.

Derivation of Raman treshold formulas for CW double-clad fiber amplifiers.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2009, Optics express.

Microjoule-level all-polarization-maintaining femtosecond fiber source.

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2006, Optics letters.

Millijoule Pulse Energy High Repetition Rate Femtosecond Fiber CPA System : Results, SHG and Scaling potential

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2008 .

Widely tuneable fiber optical parametric amplifier for coherent anti-Stokes Raman scattering microscopy.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2012, Optics express.

Hybrid 400W Fiber-Innoslab fs-Amplifier

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2009 .

Alignment-free, all-spliced fiber laser source for CARS microscopy based on four-wave-mixing.

Jens Limpert, Andreas Tünnermann, Jürgen Popp, 2012, Optics express.

94 W 980 nm high brightness Yb-doped fiber laser.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2008, Optics express.

Suppression of higher order modes in a multimode fiber amplifier using efficient gain-loss-management (GLM)

Jens Limpert, Andreas Tünnermann, Holger Zellmer, 2002 .

Generation of high-photon flux-coherent soft x-ray radiation with few-cycle pulses.

Jens Limpert, Andreas Tünnermann, Steffen Hädrich, 2013, Optics letters.

Transverse mode instability

Cesar Jauregui, Jens Limpert, Christoph Stihler, 2020, 2004.14752.

Compact high-repetition-rate source of coherent 100 eV radiation

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2013, Nature Photonics.

23 mJ high-power fiber CPA system using electro-optically controlled divided-pulse amplification.

Jens Limpert, Andreas Tünnermann, Arno Klenke, 2019, Optics letters.

Non-hexagonal Large-Pitch Fibers for enhanced mode discrimination.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2011, Optics express.

Table-Top Milliwatt-Class Extreme Ultraviolet High Harmonic Light Source

Jens Limpert, Jan Rothhardt, Stefan Demmler, 2016, 1607.03131.

The impact of spectral modulations on the contrast of pulses of nonlinear chirped-pulse amplification systems.

Jens Limpert, Andreas Tünnermann, Enrico Seise, 2008, Optics express.

4-fold increase of the mode instability threshold in an Ybdoped multi-core fiber amplifier emitting 536 W

Cesar Jauregui, Fabian Stutzki, Jens Limpert, 2014, 2014 Conference on Lasers and Electro-Optics (CLEO) - Laser Science to Photonic Applications.

Fiber-based source for multiplex-CARS microscopy based on degenerate four-wave mixing.

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2012, Optics express.

105 kHz, 85 ps, 3 MW Peak Power Microchip Laser Fiber Amplifier System

Jens Limpert, Andreas Tünnermann, Oliver Schmidt, 2008 .

Carbon chloride-core fibers for soliton mediated supercontinuum generation.

Jens Kobelke, Fabian Stutzki, Jens Limpert, 2018, Optics express.

High-power very large mode-area thulium-doped fiber laser.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2012, Optics letters.

Fiber lasers and amplifiers: an ultrafast performance evolution.

Jens Limpert, Andreas Tünnermann, Thomas Schreiber, 2010, Applied optics.

Sub 25 fs pulses from solid-core nonlinear compression stage at 250 W of average power.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2012, Optics letters.

100 W average power femtosecond laser at 343 nm.

Jens Limpert, Andreas Tünnermann, Marco Kienel, 2016, Optics letters.

Self-starting passively mode-locked chirped-pulse fiber laser.

Jens Limpert, Andreas Tünnermann, Bülend Ortaç, 2007, Optics express.

530 W, 1.3 mJ, four-channel coherently combined femtosecond fiber chirped-pulse amplification system.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2013, Optics letters.

Temperature-induced index gratings and their impact on mode instabilities in high-power fiber laser systems.

Cesar Jauregui, Tino Eidam, Hans-Jürgen Otto, 2012, Optics express.

High-average-power femtosecond laser at 258 nm.

Jens Limpert, Andreas Tünnermann, Arno Klenke, 2017, Optics letters.

Electro-optical sampling of ultrashort THz pulses by fs-laser pulses at 530 nm with BaTiO3

Jens Limpert, Andreas Tünnermann, Stefan Nolte, 2007 .

High-repetition-rate sub-5-fs pulses with 12 GW peak power from fiber-amplifier-pumped optical parametric chirped-pulse amplification.

Jens Limpert, Andreas Tünnermann, Christoph Jocher, 2011, Optics letters.

Optimization of high performance ultrafast fiber laser systems to >10 GW peak power

Jens Limpert, Andreas Tünnermann, Damian N. Schimpf, 2010 .

Dependence of the mode instability threshold of high-power fiber laser systems on core co-dopants

Cesar Jauregui, Jens Limpert, Andreas Tünnermann, 2017, 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC).

Nonlinear compression to sub-30-fs, 0.5 mJ pulses at 135 W of average power.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2013, Optics letters.

2.4 mJ, 33 W Q-switched Tm-doped fiber laser with near diffraction-limited beam quality.

Cesar Jauregui, Fabian Stutzki, Florian Jansen, 2013, Optics letters.

High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules.

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2016, Optics express.

Continuously chirped fiber Bragg gratings by femtosecond laser structuring.

Fabian Stutzki, Jens Limpert, Andreas Tünnermann, 2008, Optics letters.

High average power large-pitch fiber amplifier with robust single-mode operation.

Cesar Jauregui, Tino Eidam, Fabian Stutzki, 2011, Optics letters.

Divided Pulse Nonlinear Compression

Tino Eidam, Jens Limpert, Andreas Tünnermann, 2013 .