We report on damage-free fiber-guidance of milli-Joule energy-level and 600-femtosecond laser pulses into hypocycloid core-contour Kagome hollow-core photonic crystal fibers. Up to 10 meter-long fibers were used to successfully deliver Yb-laser pulses in robustly single-mode fashion. Different pulse propagation regimes were demonstrated by simply changing the fiber dispersion and gas. Self-compression to ~50 fs, and intensity-level nearing petawatt/cm(2) were achieved. Finally, free focusing-optics laser-micromachining was also demonstrated on different materials.

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A mode-locked thin-disk laser based on Yb:CALGO is demonstrated for the first time. At an average output power of 28 W we obtained pulses with a duration of 300 fs and a pulse energy of 1.3 μJ. 197 fs pulses with 0.9 μJ of energy were achieved at an average output power of 20 W. The shortest pulse duration measured in our experiments was 135 fs with a spectrum centered at 1043 nm. The experiments also revealed a very broad tunability from 1032 to 1046 nm with sub-200 fs pulses.

We demonstrate coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using a feedback loop based on an electro-optic phase modulator, an average power of 7.2 W before compression is obtained with a combining efficiency of 90%. The spatial and temporal qualities of the oscillator are retained, with a recombined pulse width of 325 fs. This experiment opens up a way to scale the peak/average power of ultrafast fiber sources.

We report on crater formation, line scribing and cavity milling experiments on Silicon, Copper, Aluminum and stainless steel with GHz bursts of femtosecond pulses. The intra-burst repetition rate has been varied between 0.88 and 3.52 GHz, the number of pulses per burst between 50 and 3200, the burst fluence between 8 and 80 J/cm2. For these experiments, a 100-W femtosecond GHz-burst laser has been developed on an industrial laser basis, delivering a total burst energy up to 1 mJ at 100 kHz, with an adjustable number of pulses per burst. The results highlight the conditions to obtain high-ablation efficiency, show how to optimize the machining quality and point out the burst duration as the relevant parameter for femtosecond GHz machining.

We demonstrate nonlinear temporal compression of a high-energy Yb-doped fiber laser source in a multipass cell filled with argon. The 160 μJ 275 fs input pulses are compressed down to 135 μJ 33 fs at the output, corresponding to an overall transmission of 85%. We also analyze the output beam, revealing essentially no space-time couplings. We believe this technique can be scalable to higher pulse energies and shorter pulse durations, enabling access to a wider parameter range for a large variety of ultrafast laser sources.

We report on the study of direct amplification of femtosecond pulses in an 80 mum core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a 1250 line/mm (l/mm) grating-based compressor, pulses as short as 49 fs with 870 nJ pulse energy and 12 MW peak power are obtained. Alternatively, the use of a 1740 l/mm grating allows the production of higher quality pulses of 70 fs, 1.25 microJ pulse energy, and 16 MW peak power.

We demonstrate a versatile femtosecond power amplifier using a Yb:YAG single crystal fiber operating from 10 kHz to 10 MHz. For a total pump power of 75 W, up to 30 W is generated from the double-pass power amplifier. At a repetition rate of 10 kHz, an output energy of 1 mJ is obtained after recompression. In this configuration, the pulse duration is 380 fs, corresponding to a peak power of 2.2 GW. The M 2 beam quality factor is better than 1.1 for investigated parameters. © 2013 Optical Society of America OCIS codes: 320.7090, 140.3615.Ultrafast lasers are now a common tool for scientific and industrial applications. Over the past decade, many technological developments of diode-pumped solid-state laser systems have allowed tremendous improvements of their performance, reliability, and cost. In order to achieve high energy per pulse in the femtosecond regime, master oscillator power amplifier systems are commonly used. Regenerative amplifiers based on bulk or thin disk Yb-doped crystals can amplify ultrashort pulses to several tens of millijoules [1,2]. They can provide high gain and high output energy at a low repetition rate, but they are limited in terms of repetition rate to a few hundreds of kilohertz due to the high-voltage-driven switch speed. Ytterbium-doped optical fibers can also be used to amplify ultrashort pulses. Their high surface-to-volume ratio provides good thermal management and allows attainment of high average powers of several hundreds of watts [3]. However, the signal confinement in smallcross-section cores induces nonlinear effects, such as self-phase modulation and self-focusing, which limit the peak power and the pulse energy. Femtosecond pulses with an energy of 2.2 mJ were obtained using the well-known chirped pulse amplification technique together with large-core-diameter photonic crystal fibers [4]. Another approach consists in amplifying femtosecond pulses directly in Yb-doped crystals using multipass amplifiers without active elements. Although it requires quite complex systems, the slab geometry has proven to be a very successful approach. Up to 1.1 kW [5] average power and 20 mJ [6] energy were obtained with an Yb:YAG Innoslab amplifier. Significant improvement of the emission cross section and the thermal conductivity can be observed at cryogenic temperatures in most Ybdoped crystals. 40 mJ output energy was obtained using a cryogenic Yb:YAG double-pass amplifier [7]. However, stronger spectral narrowing at low temperatures induces longer optical pulses of several picoseconds. Finally, the single crystal fiber (SCF) concept lies between fibers and crystals and can contribute to original performance for femtosecond systems. SCFs are long, thin crystal rods with a diameter lower than 1 mm and a typical length of a few centimeters.