Advanced Solid-State Lasers Congress

Advanced Solid-State Lasers Congress
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14:00-16:00
AF3A • Yb-Doped Thin Disks
Presider: Valentin Petrov; Max Born Institute, Germany
AF3A.1 • 14:00 Broadly Tunable Yb:CALGO Thin Disk Laser with High Efficiency, Kolja Beill, Christian Krankel1,2, Bastian Deppe l,2; lInstitut fiir Laser-Physik, Germany; 2'The Hamburg Centre for Ultrafast Imaging, Germany. We obtained 90 run wavelength tuning with >20 W between 1022 run and 1072 run with an Yb:CALGO thin disk laser, This is the widest tuning range of any Yb-doped material at this power leveL AF3A.2 • 14:12 62-fs Pulses from a SESAM Modelocked Yb:CALGO Thin Disk Laser, Andreas Diebold l, Florian Emauryl, Clara J. Saracenol,2, Cinia Schriber l , Matthias Gollingl, Thomas Siidmeyer2, Ursul'a Keller l; lInstitute for Quantum Electronics, ETH Zurich, Switzerland; 2Physics Institute, University of Neuchiitel, Switzerland. We demonstrate a SESAM modelocked thin-disk laser (roL) based on Yb:CALGO delivering 62 fs pulses with 5 W of average power. To our knowledge, these are the shortest pulses achieved from a modelocked TDL to-date, AF3A.3 • 14:24 Pulse Energy Scaling of an Yb:YAG Modelocked Thin Disk Laser Operated in a Pressure-controlled Nitrogen Environment, Clara J. Saraceno l,2, Florian Emauryl, Martin Hoffmann!, Cinia Schriberl, Matthias Golling!, Thomas Siidmeyer2, Ursula Kellerl ; lETH Zurich, Switzerland; 2 University of Neuchatel, Switzerland. We present energy scaling of an Yb:YAG thin disk laser operated in a pressure-controlled nitrogen environment. We obtained 29.6flJ pulse energy, 780-fs pulses and 105W of average power, corresponding to 33.3MW of output peak power. AF3A.4 • 14:36 120 W, 41-lJ from a purely Kerr-lens mode-locked Yb:YAG thin-disk oscillator,Jonathan Brons!,2, Oleg Pronin l.2, Marcus Seide)!,2, Vladimir Pervak2, Dominik Bauer3, Dirk Sutter3, Vladimir L. Kalashniko0, Alexander Apolonskp,2, Ferenc Krausz l,2; lMax-Planck-Institut for Quantenoptik, Germany; 2Ludwig-Maximilians-Universitiit Munchen, Germany; 3TRUMPF-Laser GmbH + Co. KG, GermallY; ''lnstitut for Photonik, TU Wien, Austria. We report on a pure hard-aperture Kerr-lens mode-locked Yb:YAG thin-disk oscillator delivering 120-W, 4-flJ, 350-fs in air. This is, to our knowledge, the highest average power and pulse energy achieved from KLM oscillators so far. AF3A.5 • 14:48 Carrier-envelope Phase Stabilized Thin-disk Oscillator, Oleg Proninl, Marcus SeideF, Jonathan Brons 2, Fabian Liickingl, Vladimir Pervak1, Alexander Apolonski l ,2, Thomas Udem 2, Ferenc Krausz1.2; 1 Ludwig-Maximilians-Ulliversity Munich, Germany; 2Max-Planck-Institute of Quantum Optics, Germany. Carrier-envelope phase (CEP) stabilization of thin-disk oscillator with 200 mrad RMS noise measured in out-of-loop interferometer is demonstrated for the first time. The oscillator operates with 5.5% output coupler and delivers 17 W, 0.4 flJ pulses. AF3A.6 • 15:00 Sub-50 fs, Kerr-lens Mode-locked Yb:CaF2 Laser Oscillator Delivering up to 2.7 W, Pierre Sevillano1, Guillaume Machinetl, Romain Dubrasquet2, Patrice Camy 3, Jean-Louis Doualan 3, Richard Moncorge3, Patrick Georges4, Frederic P. Druon4, Dominique Descampsl, Eric Cormier!; lCELlA, France; 2Azur light Systeme, France; 3CIMAP, France; 4[OGS-LCF, France, By means of a high-brightness optical pumping scheme with a fiber laser, we demonstrate Kerr-lens mode locking with an Yb:CaF2laser crystaL Stable 48 fs pulses are produced at an average power of 2.7 W. 80
Advanced Solid-State Laser Congress • October 2013
AF3A.4.pdf
Advanced Solid-State Lasers Congress Technical Digest ©
OSA 2013
120 W, 4 µJ from a purely Kerr-lens mode-locked Yb:YAG
thin-disk oscillator
Jonathan Brons 1,2), Oleg Pronin 1,2), Marcus Seidel 1,2), Vladimir Pervak 2), Dominik Bauer 3), Dirk Sutter 3),
Vladimir Kalashnikov 4), Alexander Apolonskiy 1,2), and Ferenc Krausz 1,2)
1)
Max-Planck-Institut für Quantenoptik, Garching, Germany
Ludwig-Maximilians-Universität München, Garching, Germany
3)
TRUMPF-Laser GmbH + Co. KG, Schramberg, Germany
4)
Institut für Photonik, TU Wien, Vienna, Austria
Author e-mail address: jonathan.brons@mpq.mpg.de
2)
Abstract: We report on a pure hard-aperture Kerr-lens mode-locked Yb:YAG thin-disk oscillator
delivering 120-W, 4-µJ, 350-fs in air. This is, to our knowledge, the highest average power and
pulse energy achieved from KLM oscillators so far.
© 2013 Optical Society of America
OCIS codes: (140.3538); (140.4050)
1. Introduction
Many scientific as well as industrial applications demand high average output power from ultrafast pulsed lasersystems at MHz repetition-rates. Today such systems are mainly represented by master oscillator power amplifier
(MOPA) setups in both bulk and fiber configuration. As an example 830 W and 620 W with sub-ps pulse duration
could be reached from a fiber chirped pulse amplifier (CPA) [1] and a single Innoslab bulk amplifier [2]
correspondingly. With ongoing development of the thin-disk (TD) technology high power mode-locked (ML) thindisk oscillators become increasingly attractive for their potentially shorter pulses, lower noise and compact setup.
The average power from an Yb:YAG SESAM-mode-locked TD oscillator was demonstrated to be 275 W [3] and
pulse energy of >40 µJ [4]. Although the gain-bandwidth of Yb:YAG should allow for sub-200 fs pulses, SESAMmode-locked TD oscillators usually deliver pulses that are longer by a factor of 3 [5] owing to the moderate
modulation-depth of these devices. The first Kerr-lens mode-locked (KLM) TD-oscillator was realized giving
experimental evidence to near bandwidth-limited 200 fs pulses from an Yb:YAG TD oscillator [6]. Recently this
oscillator was carrier-envelope-phase (CEP) stabilized opening the door to many other research applications [7].
Spectral broadening of the output of this KLM TD oscillator in a photonic-crystal fiber and subsequent compression
by chirped mirrors yielded 15 fs pulses at 20 W average power, making it a viable high-power alternative to Ti:Sa
oscillators [8]. Recently a TD KLM ring-oscillator aimed at intra-cavity high harmonic generation was realized [9].
The goal of this work is to give experimental evidence of further power-scalability of the KLM approach in TD
oscillators.
2. Experimental setup
Building a cavity for high-power TD-KLM operation is a challenging task. There are two different guidelines that
can be described independently. 1) A TEM00-mode convex-concave cavity is designed by the use of two mirrors
CM1 and CM2 [10] in Fig. 1. to provide a large mode-size over all cavity elements. This CW-cavity is designed to
operate in the center of stability such that any variations in the TD-curvature have a minimal effect on the modeshape. The Yb:YAG disk, 120 µm thick (Trumpf GmbH), pumped at 969 nm, is one of the folding mirrors. 2) A
focusing imaging section, consisting of two identical concave focusing-mirrors FM1 and FM2, can be inserted
anywhere into the CW-resonator without influencing its’ behavior. This imaging section has two purposes: a) to
provide a strong focus for the Kerr-medium (KM) and b) to bring the cavity to an edge of the stability-zone via
changing the separation-distance of FM1 and FM2 and thus making the oscillator more susceptible to the Kerr-lens
[11].The average mode-radius in the cavity is kept at ~1 mm while the mode radius on the TD is 1.2 mm. The radius
of the pump spot on the TD is 1.6 mm diameter. In previous publications a weak SESAM with <0.1% modulationdepth was used to aid the Kerr-lens in initiating the mode-locking [6, 12]. Such a weak SESAM is not necessary to
start KLM-operation and can be replaced by a hard aperture as was done in this work (see Fig. 1(b)). Mode-locking
could also be initiated with just the soft aperture of the TD. This pure soft-aperture starting-procedure is very harsh
however, creating audible q-switching intensity-peaks that often lead to damage of the Kerr- medium. In contrast, a
hard-aperture strongly increases the stability and makes starting reliable and not very sensitive to the cavity
alignment.
AF3A.4.pdf
Advanced Solid-State Lasers Congress Technical Digest ©
OSA 2013
Fig. 1. a) Sketch of the cavity (not to scale): OC: output coupler with 14% transmission, TD: Yb:YAG thin-disk, HD: high dispersive mirrors
with ~ -3000 fs² per bounce, CM1/2: curved mirrors 1/2, FM1/2: focusing mirrors 1/2, KM: 1 mm thick sapphire-plate placed in the focus of
FM1&2, HR: high reflectivity end-mirror. b) Image of the water cooled copper-aperture, the Kerr-medium on a translation-stage and the endmirror. c) Beam-profile of the 120 W oscillator-output. d) poor overlap of the KLM-mode with the pumped region on the TD (fluorescence).
3. Results and discussion
By increasing the distance between the two focusing mirrors FM1 and FM2 (Fig. 1.) we can approach the stabilityedge of the cavity and mode-lock the oscillator through perturbation of one of the focusing mirrors. With a 1 mm
thick sapphire window as Kerr-medium, a total roundtrip GDD of -24000 fs² and 14% output coupler (OC) the
average power of 120 W could be measured from the described oscillator, corresponding to 4.1 µJ pulse-energy at
29 MHz repetition rate. Autocorrelation and spectrum traces indicate near Fourier-limited 350 fs sech pulses. The
average power of 120 W is achieved at 600 W pump power corresponding to a 20% percent optical to optical
efficiency. This efficiency can be considerably improved by adjusting the poor overlap of pump profile and cavitymode depicted in Fig. 1. This should also lead to a shorter pulse-duration. The same cavity with the imaging-focal
lengths of 250 mm and a 10 % output-coupler delivered 300 fs pulses at 60 W average output power with 2 µJ pulse
energy.
Fig. 2. a) Autocorrelation trace for 65 W output from oscillator with 250 mm focal length focusing-mirrors.
trace and spectrum for 120 W output from oscillator with 350 mm focal length focusing-mirrors.
. b) Autocorrelation
.
Compared to a previously published cavity-configuration [6] this resonator has approximately 4 and 1.4 times larger
100
and 70 ) for the different focal lengths 350 mm and 250 mm of
mode-radii in the Kerr-medium (
the imaging systems respectively. Thus the same self-phase modulation can be achieved by increasing the intracavity peak power by a factor of 4 or 2. We would intuitively anticipate an increase in pulse-energy by the same
factors 4 and 2 as long as all other parameters stay fixed. This consideration does not take into account the resulting
longer focal length of the thin Kerr-lens but comparing the intra-cavity pulse-energies of 8, 18 and 29 µJ (150 [6],
250 and 350 mm focal lengths) shows a remarkable correspondence. An estimate of the total nonlinear phase-shift
inside the cavity identifies the Kerr-medium (>90%) as main contributor in this 30 MHz-cavity while air contributes
AF3A.4.pdf
Advanced Solid-State Lasers Congress Technical Digest ©
OSA 2013
<10%. Thus scaling via the KM seems justified and going to vacuum is not necessary for the current cavity
configuration. Using fused silica as Kerr medium at average intra-cavity powers near 1 kW reproducibly resulted in
a strong thermal lens located in the Kerr medium appearing on the order of < 1second after initiation of ML. This
thermal lens then broke the mode-locked operation and forced oscillation in CW. Employing sapphire with a thermal
conductivity ~ 30 times higher than fused silica resulted in stable operation without thermal lens. A strong
correlation between the oscillator’s intensity noise (Fig. 4.) in the high-frequency range (1-4 kHz) and the flow-rate
of the TD cooling is investigated. Future attempts to the oscillator’s intensity-noise will require a less aggressive
cooling approach. The dependence of the oscillator noise on the TD cooling water flow is shown in Fig. 4. At 1.0
l/min coolant flow the oscillator noise hits the noise floor of the oscilloscope in the range of 1 - 4 kHz.
Fig. 3. Intensity noise of the oscillator with 1, 1.2 and 3 l/min cooling-flow on the TD.
4. Conclusion
We demonstrate a KLM Yb:YAG TD oscillator delivering 120 W avg. power and 4.1 µJ pulses with 350 fs duration
in air environment. Suffering no thermal instabilities from a sapphire Kerr-medium we expect to scale the power
further above 150 W. The TD coolant was identified as a strong contributor to noise in the oscillator which can be
significantly reduced at a flow rate around 1 l/min.
5. References
[1] T. Eidam, S. Hanf, E. Seise, T. V. Andersen, T. Gabler, C. Wirth, T. Schreiber, J. Limpert, and A. Tünnermann, “Femtosecond fiber CPA
system emitting 830 W average output power,” Opt. Lett. 35, 2, 94-96 (2010).
[2] P. Russbueldt, T. Mans, J. Weitenberg, H. D. Hoffmann, and R. Poprawe, “Compact diode-pumped 1.1 kW Yb:YAG Innoslab femtosecond
amplifier,” Opt. Lett. 35, 24, 4169-4171 (2010).
[3] C. J. Saraceno, F. Emaury, O. H. Heckl, C. R. E. Baer, M. Hoffmann, C. Schriber, M. Golling, T. Südmeyer, and U. Keller, “275 W average
output power from a femtosecond thin disk oscillator operated in a vacuum environment,” Opt. Express 20, 21 (2012).
[4] C. J. Saraceno, C. Schriber, F. Emaury, O. H. Heckl, C. R. E. Baer, M. Hoffmann, K. Beil, C. Kränkel, M. Golling, T. Südmeyer, and U.
Keller, “Cutting-Edge High-Power Ultrafast Thin Disk Oscillators,” Appl. Sci. 3, 355-395 (2013).
[5] D. Bauer, I. Zawischa, D. H. Sutter, A. Killi, and T. Dekorsy, “Mode-locked Yb:YAG thin-disk oscillator with 41 µJ pulse energy at 145 W
average infrared power and high power frequency conversion,” Opt. Express 20, 9, 9698–9704 (2012).
[6] O. Pronin, J. Brons, C. Grasse, V. Pervak, G. Boehm, M.-C. Amann, V. L. Kalashnikov, A. Apolonski, und F. Krausz, “High-power 200 fs
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[7] O. Pronin, M. Seidel, J. Brons, F. Lücking, V. Pervak, A. Apolonski, T. Udem, and F. Krausz, “CEP stable thin-disk oscillator,” Advanced
Solid-State Lasers submitted (2013).
[8] M. Seidel, O. Pronin, J. Brons, V. Pervak, A. Apolonskiy, and F. Krausz, “Approaching the Few-Cycle Pulse Regime with Thin-Disk
Oscillators,” Advanced Solid-State Lasers submitted (2013).
[9] A. A. Eilanlou, Y. Nabekawa, M. Kuwata-Gonokami, and K. Midorikawa, “Kerr lens mode-locking of a high-average-power thin-disk ring
oscillator“, in CLEO: 2013 Technical Digest, CTh1H.3 (Optical Society of America 2013).
[10] W. Koechner, Solid-State Laser Engineering, 7th ed. Springer, 2006.
[11] V. Magni, G. Cerullo, and S. De Silvestri, “Closed form gaussian beam analysis of resonators containing a Kerr medium for femtosecond
lasers,” Optics Communications 101, 5–6, 365–370 (1993).
[12] O. Pronin, J. Brons, C. Grasse, V. Pervak, G. Boehm, M.-C. Amann, A. Apolonski, V. L. Kalashnikov, and F. Krausz, “High-power Kerrlens mode-locked Yb:YAG thin-disk oscillator in the positive dispersion regime“, Opt. Lett. 37, 17, 3543–3545 (2012).