Gaponenko, Maxim

, Gaponenko, Maxim, Kuleshov, Nikolay, Südmeyer, Thomas

We present the first passively Q-switched thulium microchip laser. The diode-pumped laser incorporates a Tm:KYW gain medium and an InGaAs semiconductor saturable absorber mirror. The laser emits pulses with a duration of 2.4 ns at a repetition rate of 1.2 MHz with an average output power of 130 mW at a wavelength of 1905 nm. It operates in a fundamental TEM₀₀ mode with M² < 1.1. The Q-switched pulse train is very stable with pulse-to-pulse intensity fluctuations <10% and a timing jitter of < ± 50 ns. Our microchip laser appears well suited as a seed in pulsed 2-μm fiber amplifier systems for applications like material processing. In addition, we present new power scaling results for continuous-wave Tm-microchip lasers, achieving 1.6 W of output power in a fundamental TEM₀₀ mode. The slope efficiency relative to the absorbed pump power is as high as 74%, and the optical-to-optical efficiency is 41%. A maximum output power of 2.6 W is achieved in a TEM_01∗-doughnutlike transverse mode. In all the cases, no active cooling is applied to the gain medium.

, Labaye, François, Gaponenko, Maxim, Wittwer, Valentin, Diebold, A, Paradis, Clément, Modsching, Norbert Paul, Merceron, Loïc, Emaury, F, Graumann, I.J, Phillips, C.R, Saraceno, C.J, Kränkel, C, Keller, Ursula, Südmeyer, Thomas

We demonstrate a compact extreme ultraviolet (XUV) source based on high-harmonic generation (HHG) driven directly inside the cavity of a mode-locked thin-disk laser oscillator. The laser is directly diode-pumped at a power of only 51 W and operates at a wavelength of 1034 nm and a 17.35 MHz repetition rate. We drive HHG in a high-pressure xenon gas jet with an intracavity peak intensity of 2.8×10¹³  W/cm² and 320 W of intracavity average power. Despite the high-pressure gas jet, the laser operates at high stability. We detect harmonics up to the 17th order (60.8 nm, 20.4 eV) and estimate a flux of 2.6×10⁸  photons/s for the 11th harmonic (94 nm, 13.2 eV). Due to the power scalability of the thin-disk concept, this class of compact XUV sources has the potential to become a versatile tool for areas such as attosecond science, XUV spectroscopy, and high-resolution imaging.

, Modsching, Norbert, Drs, Jakub, Fischer, Julien, Paradis, Clément, Labaye, François, Gaponenko, Maxim, Kränkel, Christian, Wittwer, Valentin, Südmeyer, Thomas

We investigate power-scaling of a Kerr lens mode-locked (KLM) Yb:Lu₂O₃ thin-disk laser (TDL) oscillator operating in the sub-100-fs pulse duration regime. Employing a scheme with higher round-trip gain by increasing the number of passes through the thin-disk gain element, we increase the average power by a factor of two and the optical-to-optical efficiency by a factor of almost three compared to our previous sub-100-fs mode-locking results. The oscillator generates pulses with a duration of 95 fs at 21.1 W average power and 47.9 MHz repetition rate. We discuss the cavity design for continuous-wave and mode-locked operation and the estimation of the focal length of the Kerr lens. Unlike to usual KLM TDL oscillators, an operation at the edge of the stability zone in continuous-wave operation is not required. This work shows that KLM TDL oscillators based on the gain material Yb:Lu₂O₃ are an excellent choice for power-scaling of laser oscillators in the sub-100-fs regime, and we expect that such lasers will soon operate at power levels in excess of hundred watts.

, Gaponenko, Maxim, Kuleshov, Nikolay, Südmeyer, Thomas

We report on a diode-pumped Tm:KYW microchip laser generating 1 W continuous-wave output power. The laser operates at a wavelength of 1.94 μm in the fundamental TEM₀₀ mode with 71% slope efficiency relative to the absorbed pump radiation and 59% slope efficiency relative to the incident pump radiation. The optical-to-optical laser efficiency is 43%.

, Jornod, Nayara, Wittwer, Valentin, Gaponenko, Maxim, Hoffmann, Martin, Hempler, Nils, Malcolm, Graeme P. A, Maker, Gareth T, Südmeyer, Thomas

We report the first optical parametric oscillator synchronously pumped by a SESAM modelocked vertical external-cavity surface-emitting laser (VECSEL). As a nonlinear medium, we use a periodically poled MgO:PPLN crystal. The VECSEL operates at a wavelength of 982 nm and a repetition rate of 198 MHz. The pump radiation is converted to signal and idler wavelengths tunable in the ranges of 1.4-1.8 μm and 2.2-3.5 μm, respectively, simply by a change of the poling period and crystal temperature. The signal pulses have a duration between 2 ps to 4 ps and an average output power up to 100 mW.

, Labaye, François, Gaponenko, Maxim, Modsching, Norbert, Brochard, Pierre, Paradis, Clément, Schilt, Stephane, Wittwer, Valentin Johannes, Südmeyer, Thomas

Ultrafast thin-disk laser (TDL) oscillators provide higher intracavity pulse energy, average power, and peak power levels than any other femtosecond laser oscillator technology. They are suitable for driving extreme nonlinear interactions directly inside the laser oscillator. High harmonic generation (HHG) driven inside ultrafast TDL oscillators is a very recent approach for the generation of coherent extreme ultraviolet (XUV) light at multi-megahertz repetition rates. In this paper, we review the current state of the development, discuss the technological potential, and give an outlook toward the future developments. We compare the current performance to established technologies and evalu-ate possible limitations. We discuss future improvements, such as reduction of the driving pulse duration and increase of the intracavity peak power, efficient extraction of the XUV light from the cavity, and carrier-envelope offset frequency stabilization of the generated XUV light. Due to the power scalability of the TDL concept and the possibility to operate in a spectrally broadened regime with pulse durations below the gain bandwidth limitation, intra-oscillator HHG with TDLs has a high potential for powerful table-top multi-megahertz coherent XUV light sources for science and applications.

, Modsching, Norbert, Paradis, Clément, Labaye, François, Gaponenko, Maxim, Graumann, Ivan J, Diebold, Andreas, Emaury, Florian, Wittwer, Valentin, Südmeyer, Thomas

We demonstrate the first Kerr lens mode-locked Yb:CaGdAlO₄ (Yb:CALGO) thin-disk laser oscillator. It generates pulses with a duration of 30 fs at a central wavelength of 1048 nm and a repetition rate of 124 MHz. The laser emits the shortest pulses generated by a thin-disk laser oscillator, equal to the shortest pulse duration obtained by Yb-doped bulk oscillators. The average output power is currently limited to 150 mW by the low gain and limited disk quality. We expect that more suitable Yb:CALGO disks will enable substantially higher power levels with similar pulse durations.