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R. Peters,
C. Kränkel,
S. T. Fredrich-Thornton,
K. Beil,
K. Petermann,
G. Huber, O. H. Heckl,
C. R. E. Baer,
C. J. Saraceno,
T. Südmeyer,
U. Keller
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ABSTRACT: We report on thermal conductivity analysis and thin disk laser power scaling of Yb:Lu2O3, Yb:Sc2O3, and Yb:LuScO3. Using a volume Bragg-grating stabilized pump diode we have obtained cw output powers up to 301W with optical-to-optical
efficiencies of up to 73%. In mode-locked operation of an Yb:Lu2O3 thin disk laser 141W of average output power with 738 fs pulses and an optical-to-optical efficiency of 40% were achieved.
Applied Physics B 04/2012; 102(3):509-514. · 2.19 Impact Factor
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ABSTRACT: Ultrafast thin disk laser oscillators achieve the highest average output powers and pulse energies of any mode-locked laser
oscillator technology. The thin disk concept avoids thermal problems occurring in conventional high-power rod or slab lasers
and enables high-power TEM00 operation with broadband gain materials. Stable and self-starting passive pulse formation is achieved with semiconductor
saturable absorber mirrors (SESAMs). The key components of ultrafast thin disk lasers, such as gain material, SESAM, and dispersive
cavity mirrors, are all used in reflection. This is an advantage for the generation of ultrashort pulses with excellent temporal,
spectral, and spatial properties because the pulses are not affected by large nonlinearities in the oscillator. Output powers
close to 100W and pulse energies above 10μJ are directly obtained without any additional amplification, which makes these
lasers interesting for a growing number of industrial and scientific applications such as material processing or driving experiments
in high-field science. Ultrafast thin disk lasers are based on a power-scalable concept, and substantially higher power levels
appear feasible. However, both the highest power levels and pulse energies are currently only achieved with Yb:YAG as the
gain material, which limits the gain bandwidth and therefore the achievable pulse duration to 700 to 800fs in efficient thin
disk operation. Other Yb-doped gain materials exhibit a larger gain bandwidth and support shorter pulse durations. It is important
to evaluate their suitability for power scaling in the thin disk laser geometry. In this paper, we review the development
of ultrafast thin disk lasers with shorter pulse durations. We discuss the requirements on the gain materials and compare
different Yb-doped host materials. The recently developed sesquioxide materials are particularly promising as they enabled
the highest optical-to-optical efficiency (43%) and shortest pulse duration (227fs) ever achieved with a mode-locked thin
disk laser.
Applied Physics B 04/2012; 97(2):281-295. · 2.19 Impact Factor
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O. H. Heckl,
C. R. E. Baer,
C. Kränkel,
S. V. Marchese,
F. Schapper,
M. Holler,
T. Südmeyer,
J. S. Robinson,
J. W. G. Tisch,
F. Couny,
P. Light,
F. Benabid,
U. Keller
[show abstract]
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ABSTRACT: High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31,
1988; McPherson et al., J. Opt. Soc. Am. B 4:595, 1987) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly
focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is
limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature
424:831, 2003; Südmeyer et al., Nat. Photonics 2:599, 2008; Röser et al., Opt. Lett. 30:2754, 2005; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, 2009) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the
harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped
multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average
power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times,
and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies
were developed: external build-up cavities (Gohle et al., Nature 436:234, 2005; Jones et al., Phys. Rev. Lett. 94:193, 2005) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, 2008). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality,
and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, 2003; Ren et al., Opt. Express 16:17052, 2008; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, 2004; Serebryannikov et al., Opt. Lett. 33:977, 2008; Zhang et al., Nat. Phys. 3:270, 2007). The interaction between the laser pulses and the gas occurs in a Kagome-type Hollow-Core Photonic Crystal Fiber (HC-PCF)
(Benabid et al., Science 298:399, 2002), which reduces the detection threshold for HHG to only 200nJ. This novel type of fiber guides nearly all of the light in
the hollow core (Couny et al., Science 318:1118, 2007), preventing damage even at intensities required for HHG. Our fiber guided 30-fs pulses with a pulse energy of more than
10μJ, which is more than five times higher than for any other photonic crystal fiber (Hensley et al., Conference on Lasers
and Electro-Optics (CLEO), IEEE Press, New York, 2008).
Applied Physics B 04/2012; 97(2):369-373. · 2.19 Impact Factor
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ABSTRACT: We present for the first time to the best of our knowledge a systematic study of lifetime and damage of semiconductor saturable absorber mirrors (SESAMs) designed for operation in high-power oscillators. We characterize and compare nonlinear reflectivity and inverse saturable absorption (ISA) parameters as well as damage threshold and lifetime of different representative SESAMs under test using a nonlinear reflectivity measurement setup at unprecedented high fluence levels. We investigate the catastrophic damage that occurs at very high fluences by demonstrating a dependence of the damage threshold on the ISA parameter F<sub>2</sub> and the maximum reflectivity fluence F<sub>0</sub>. We can clearly demonstrate that the damage fluence F<sub>d</sub> scales proportionally to √F<sub>2</sub> for all SESAMs. In the case of SESAMs with the same absorber where the product F<sub>sat</sub> .ΔR is constant, the damage fluence F<sub>d</sub> scales proportionally to F<sub>0</sub>. Therefore, damage occurs due to heating of the lattice by the energy absorbed due to the ISA process and is not related to the quantum well (QW) absorbers. Furthermore, we present guidelines on how to design samples with high saturation fluences, reduced induced absorption, and high damage thresholds. Using multiple QWs and a suitable di-electric topsection, we achieved SESAMs with saturation fluences >;200 μj/cm<sup>2</sup>, nonsaturable losses <;0.1%, and reduced ISA. Our best sample could not be damaged at a maximum available fluence of 0.21 J/cm<sup>2</sup> and a peak intensity of 370 GW/cm<sup>2</sup>. These SESAMs will be suitable for future high-power femtosecond oscillators in the kilowatt average output power regime, which is very interesting for attosecond science and industrial material processing applications.
IEEE Journal of Selected Topics in Quantum Electronics 03/2012; · 3.78 Impact Factor
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ABSTRACT: In this study we demonstrate the suitability of Hollow-Core Photonic Crystal Fibers (HC-PCF) for multiwatt average power pulse compression. We spectrally broadened picosecond pulses from a SESAM mode-locked thin disk laser in a xenon gas filled Kagome-type HC-PCF and compressed these pulses to below 250 fs with a hypocycloid-core fiber and 470 fs with a single cell core defect fiber. The compressed average output power of 7.2 W and 10.2 W at a pulse repetition rate of approximately 10 MHz corresponds to pulse energies of 0.7 µJ and 1 µJ and to peak powers of 1.6 MW and 1.7 MW, respectively. Further optimization of the fiber parameters should enable pulse compression to below 50 fs duration at substantially higher pulse energies.
Optics Express 09/2011; 19(20):19142-9. · 3.59 Impact Factor
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ABSTRACT: The authors present the first thin-disk laser based on the new sesquioxide material Yb:(Sc,Y,Lu)<sub>2</sub>O<sub>3</sub> (Yb:ScYLO). The emission cross section exhibits a peak at 1037 nm and an emission bandwidth of 18.5 nm FWHM, making this material an interesting candidate for short-pulse generation. For the initial cw multimode laser experiments we used a 200 μm thick 3 at.%-doped Yb:ScYLO disk as an active mirror in a simple linear resonator consisting only of an output coupler with a radius of curvature of 100 mm and a highly reflective disk at a distance of 7 cm. The authors pumped the disk at the zero-phonon line using a Volume Bragg Grating stabilized fiber-coupled laser diode emitting at 976 nm with an emission bandwidth of 0.6 nm. The pump module supports 24 absorption passes through the disk. With a 1,9-mm pump spot diameter on the disk and an outcoupling rate of 2.1%, the authors obtained an output power of 50 W for 90.4 W of pump power. This corresponds to an optical-to optical efficiency of 55% and a slope efficiency of 72%.
Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 06/2011
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ABSTRACT: We present the first cw and modelocked thin-disk laser based on the broadband sesquioxide material Yb:(Sc, Y, Lu)<sub>2</sub>O<sub>3</sub>. We demonstrate 50 W in cw operation with a slope efficiency >;70% and 3.9 W in 236-fs pulses in modelocked operation.
Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
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ABSTRACT: We report on two pulse compressors for a high-power thin disk laser oscillator using rod-type fiber amplifiers. Both systems are seeded by a standard SESAM modelocked thin disk laser that delivers 16 W of average power at a repetition rate of 10.6 MHz with a pulse energy of 1.5 μJ and a pulse duration of 1 ps. We discuss two results with different fiber parameters with different trade-offs in pulse duration, average power, damage and complexity. The first amplifier setup consists of a Yb-doped fiber amplifier with a 2200 μm2 core area and a length of 55 cm, resulting in a compressed average power of 55 W with 98-fs pulses at a repetition rate of 10.6 MHz. The second system uses a shorter 36-cm fiber with a larger core area of 4500 μm2. In a stretcher-free configuration we obtained 34 W of compressed average power and 65-fs pulses. In both cases peak powers of > 30 MW were demonstrated at several μJ pulse energies. The power scaling limitations due to damage and self-focusing are discussed.
Optics Express 01/2011; 19(2):1395-407. · 3.59 Impact Factor
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ABSTRACT: Yb:YCOB is a very attractive material for femtosecond pulse generation given its broad emission bandwidth. We demonstrate continuous-wave power scaling in the thin disk geometry to the 100-W level with a 40% optical-to-optical efficiency in multi-mode operation. Furthermore, we present initial modelocking results in the thin disk geometry, achieving pulse durations as short as 270 fs. The modelocked average power is, however, limited to less than 5 W because of transverse mode degradation. This is caused by anisotropic thermal aberrations in the 15% Yb-doped thin disks which were 300 to 400 µm thick. This result confirms the potential of Yb:YCOB to generate short femtosecond pulses in the thin disk geometry but also makes clear that significantly thinner disks are required to overcome the thermal limitations for high power operation.
Optics Express 08/2010; 18(18):19201-8. · 3.59 Impact Factor
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ABSTRACT: We present successful power-scaling of an Yb:Lu(2)O(3) thin disk laser to record high-power levels both in cw and mode-locked operation. In a simple multimode resonator we achieved 149 W of output power in cw operation with 73% optical-to-optical efficiency (eta(opt)). Building an 81 MHz fundamental transverse mode resonator with dispersion compensation and a semiconductor saturable absorber mirror (SESAM) for passive mode locking we achieved 63 W of average power in 535 fs pulses (eta(opt)=35%). The output beam is nearly diffraction limited (M(2)<1.2). The 0.78 microJ pulses with a peak power of 1.28 MW had a central wavelength of 1034 nm and were close to the Fourier transform limit. With an SESAM with a larger modulation depth we obtained pulses as short as 329 fs at 40 W average power corresponding to a pulse energy of 0.49 microJ and a peak power of 1.32 MW.
Optics Letters 09/2009; 34(18):2823-5. · 3.40 Impact Factor
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ABSTRACT: The highest average output power and pulse energy from mode-locked laser oscillators are currently achieved using semiconductor saturable absorber mirror (SESAM) mode-locked thin disk lasers (TDL). The new mixed sesquioxide Yb:LuScO<sub>3</sub> provides a nearly doubled gain bandwidth compared to Yb:Lu<sub>2</sub>O<sub>3</sub> of more than 20 nm and supports the generation of significantly shorter pulses. Here we present the results of our experiments on SESAM mode-locking of this material in the TDL setup. In a 66.5-MHz cavity the Yb(3%):LuScO<sub>3</sub> thin disk of 250 mum thickness was used as a folding mirror. A fiber coupled diode with an emission bandwidth of 3 nm at the center wavelength of 976 nm was used as a pump source in a TDL head with 24 passes of the pump light through the gain medium. The cavity contained two dispersive mirrors introducing a total of ~2200 fs<sup>2</sup> of negative group delay dispersion (GDD) per cavity roundtrip. A 5-mm thick fused silica plate was inserted at Brewster's angle and is accountable for the self-phase modulation required in soliton mode-locked lasers.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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ABSTRACT: In this work, we demonstrate the successful power scaling of Yb:Lu<sub>2</sub>O<sub>3</sub> in pulsed and cw-operation. We used an Yb:Lu<sub>2</sub>O<sub>3</sub> disk with a thickness of 250 Im and a Yb-doping concentration of 2%. The disk was pumped at 976 nm with a 0.5 nm broad fiber coupled diode. The pump spot diameter was 1.9 mm. In a simple multimode resonator with a curved outcoupling mirror (R = 100 mm, T = 2.7%) we obtained 149 W continuous wave (cw) output power at 1034 nm. The incident pump power was 204 W, which corresponds to an optical-to- optical efficiency (77opt) of 73%. This is the highest output power reported from an Yb:Lu<sub>2</sub>O<sub>3</sub> laser so far.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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O.H. Heckl,
C.R.E. Baer,
C. Krankel,
S.V. Marchese,
F. Schapper,
M. Holler,
T. Sudmeyer,
J.S. Robinson,
J.W.G. Tisch,
F. Couny,
P. Light,
F. Benabid,
P.S.J. Russell,
U. Keller
[show abstract]
[hide abstract]
ABSTRACT: Hollow-core photonic crystal fibers (HC-PCF) offer a combination of long effective interaction length and small mode areas which has resulted in several major breakthroughs in low-power nonlinear optics. Recently, it was shown numerically that such fibers offer unique properties in terms of efficiency and low threshold for high harmonic generation. In addition to the substantial decrease in pump threshold, the efficiency is expected to be significantly enhanced by guiding and improved phase-matching using optimized dispersion engineering in PCFs. This paper presents the high harmonic generation (HHG) in a HC-PCF. An extremely low threshold pulse energy for HHG of 440 nJ is observed.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
