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We report on silicon ablation with a 20 W GHz amplified femtosecond laser source. This novel laser delivers burst energies up to 400 μJ, providing flexible intra-pulse repetition rates of 0.88 or 3.52 GHz, up to 200 pulses with ∼350 fs pulse duration. High-efficiency, high-quality ablation can be achieved through optimally determining the number of pulses, intra-pulse repetition, and average pulse energy within a burst. Due to such optimization, we demonstrate a specific ablation rate of 2.5 mm3/min/W with a burst containing 200 pulses at 0.88 GHz, which is the highest one reported so far for fs laser ablation, to the best of our knowledge. GHz ablation is sensitive to the selection of laser parameters. We conceptually discuss the contributions of the pulses within a burst to heat-accumulation-based incubation and material ablation.

International audience; 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.

International audience; We propose and demonstrate an architecture that achieves passive coherent combination of two femtosecond fiber chirped-pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac interferometer. The experiment shows that the temporal, spectral, and spatial qualities of each beam are retained, with the generation of 250 fs pulses at 35MHz repetition rate, an uncompressed average power of 10W, and a combining efficiency of 96%. The behavior of this architecture in the presence of high accumulated nonlinear phase is investigated.

We demonstrated that Yb:YAG single crystal fibers have a strong potential for the amplification of femtosecond pulses. Seeded by 230 fs pulses with an average power of 400 mW at 30 MHz delivered by a passively mode-locked Yb:KYW oscillator, the system produced 330 fs pulses with an average power of 12 W. This is the shortest pulse duration ever produced by an Yb:YAG amplifier. The gain in the single crystal fiber reached a value as high as 30 in a simple double-pass configuration.

International audience; 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 7:2W 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.

A new concept of laser resonator, which uses two binary transmittance filters in two conjugated Fourier planes, can synthesize various optical waves. We have implemented this method on a Nd:YAG oscillator and produced high-energy (>200-mJ) short-duration pulses with uniform amplitude and spatial phase distribution on a circular cross section.

We report the use of gain guiding in a Ti:Al(2)O(3) rod to produce 150-mJ tunable pulses from a flat-flat resonator with an excellent efficiency. The output beam is Gaussian and 1.3 times diffraction limited.

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 report the generation of 63 fs pulses of 290 nJ energy and 4.1 MW peak power at 1050 nm based on the use of a polarization-maintaining ytterbium-doped fiber parabolic amplification system. We demonstrate that operation of the amplifier beyond the gain bandwidth limit plays a key role on the sufficient recompressibility of the pulses in a standard grating pair compressor. This results from the accumulated asymmetric nonlinear spectral phase and the good overall third-order dispersion compensation in the system.

International audience; We demonstrate spectral coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using active phase stabilization based on an electro-optic phase modulator, an average power of 10 W before compression and a high gain factor of 30 dB are obtained. At this gain value, 130 fs pulses with a spectral width of 19 nm can be generated, highlighting the strong potential of pulse synthesis for the reduction of the minimum duration of ultrashort pulses in fiber chirped-pulse amplifiers.

International audience; We implement both chirped pulse amplification and divided pulse amplification in the same femtosecond fiber amplifier setup. This scheme allows an equivalent stretched pulse duration of 2.4 ns in a compact tabletop system. The generation of 77 W of compressed average power at 4.8 MHz, together with 320 fs and 430 μJ pulses at a repetition rate of 96 kHz, is demonstrated using a distributed mode-filtering, rod-type, ytterbium-doped fiber. Limitations in the temporal recombining efficiency due to gain saturation inside the fiber amplifier are identified. A very efficient way of scaling the energy of amplified femtosecond pulses was provided by the chirped-pulse amplification (CPA) method [1]. This technique consists in temporally spreading the ultrashort pulse prior to amplification using a highly dispersive optical setup, thereby reducing the peak power by up to four orders of magnitude. This process can be reversed after the amplification to reveal the true amplified peak power. Although CPA is used in virtually every amplified femtosecond system, its implementation is increasingly difficult and costly when the desired stretched pulse duration is greater than 1 ns, due to the increasing size of the gratings and overall optical setup. Such long stretched pulse durations are therefore not used for compact tabletop or industrial systems. The divided-pulse amplification (DPA) idea was proposed more recently [2] and is similar to CPA in the sense that it also consists in redistributing the pulse energy over a time interval larger than the initial pulse width to reduce the peak power. In this scheme, a train of several orthogonally polarized delayed pulse replicas is generated and amplified before final recombination. The technique has been successfully implemented to amplify picosecond pulses [3,4], for which it is difficult to use the CPA method because of the small optical bandwidth available. It has also been used to amplify femtosecond pulses in the parabolic regime [5], which necessitates un-chirped pulses at the input of the amplifier. In both cases the delay between two successive replicas was of the order of a few picoseconds and was therefore advantageously realized using centimeter-long, highly birefrin-gent vanadate crystals. In this Letter, we propose and demonstrate for the first time a femtosecond fiber amplifier that uses both concepts simultaneously to scale the output energy of a ta-bletop femtosecond fiber system. Because the CPA stretched-pulse duration is of the order of hundreds of picoseconds, the DPA delays are implemented using free-space interferometers with reasonable arm lengths of up to 1.32 m. Because the energy of the amplified pulses is not negligible compared to the saturation energy of the fiber amplifier, a decrease of the temporal combining efficiency appears, related to the different levels of saturation of the gain medium seen by the replicas in the train, leading to different phase accumulations due to self-phase modulation (SPM) and Kramers–Krönig (K–K) effects. Despite this limitation, our experiment allows the generation of 320 fs, 430 μJ pulses at a repetition rate of 96 kHz, corresponding to 42 W average power, using a distributed mode filtering (DMF) rod-type large-mode-area fiber [6] with a combining efficiency of 82%. The 1.2 m × 0.4 m footprint experimental arrangement is depicted in Fig. 1. The DPA setup is included inside a moderately nonlinear fiber CPA in which the impact of nonlinearities can be partially compensated by the dispersion mismatch of the stretcher and compressor units [7]. The front end is composed of a passively mode-locked ultrafast oscillator, a pulse picker, a stretcher, and a low-power fiber preamplifier. The oscillator generates pulses at the central wavelength of 1030 nm and pulse duration of 200 fs. The repetition rate of the oscil-lator of 25 MHz is divided by an acousto-optic modulator pulse picker. In this experiment, two repetition rates of 4.8 MHz and 96 kHz are selected to investigate the linear and nonlinear regimes, respectively. The stretching ratio is designed to preserve a pulse duration above 500 ps after the power amplifier when operated at maximum gain. The low-power fiber preamplifier is used to boost the average power to a few tens of mW to ensure efficient operation of the power amplifier. An optical isolator is placed after the front end to prevent any optical feedback

We report the use of cross-polarized wave generation to perform both pulse shortening and temporal cleaning of a high-energy ytterbium-doped fiber-based femtosecond laser system. The nonlinear processes allow both a highly efficient nonlinear conversion of 20% and a large compression ratio of 3.5, with inherently improved coherent and incoherent contrasts. This results in the generation of 37 μJ, 115 fs pulses at a repetition rate of 100 kHz with high temporal quality.

International audience; We present a diode-pumped regenerative amplifier based on an Yb:CaF2 crystal optimized to produce short pulses for various repetition rates ranging from 100 Hz to 10 kHz. The shortest pulse duration generated is 178 fs, and the corresponding energy is 1:4 mJ before compression (620 μJ after), at a repetition rate of 500 Hz for 16 W of pump power. The bandwidth is 10 nm centered at 1040 nm. Higher repetition rate regimes have also been explored, allowing an optical-to-optical efficiency up to 10% at a high repetition rate.

We report on a compact double-stage ytterbium-doped-fiber chirped-pulse amplifier system delivering high temporal quality 270 fs pulses of 100 microJ energy at a repetition rate of 300 kHz resulting in a peak power of 340 MW. The recompression down to 1.1 times the Fourier limit is based on the exploitation of nonlinear phase shifts associated with mismatched stretcher-compressor units. A 1-m-long ytterbium-doped 80 mum core diameter photonic crystal fiber is implemented as the power amplifier and allows the production of 143 microJ pulses before compression with an accumulated B integral of 17 rad throughout the amplification stages.