Pierre Sevillano

32-fs Kerr-lens mode-locked Yb:CaGdAlO 4 oscillator optically pumped by a bright fiber laser

In this study, we report on a pure Kerr-lens mode-locked Yb:CaGdAlO₄ oscillator optically pumped by a diffraction-limited fiber laser. At the repetition rate of 96 MHz, several configurations have been studied to achieve either pulse duration of 40 fs with average powers up to the watt level or shorter pulse duration down to 32 fs. To the best of our knowledge, this represents the shortest pulse duration ever achieved with an Yb-doped bulk material and the highest average power for sub-40-fs Kerr-lens mode-locked Yb-bulk oscillator.

High-brightness fiber laser-pumped 68 fs-2.3 W Kerr-lens mode-locked Yb:CaF2 oscillator.

By using a high-brightness fiber pump laser, we demonstrate a pure Kerr-lens mode-locked (ML) Yb:CaF(2) oscillator. The laser delivers 68 fs pulses with 2.3 W average power at 73 MHz repetition rate and an optical-to-optical efficiency of 33% is achieved. To the best of our knowledge, this is the first demonstration of Kerr-lens mode-locking in Yb:CaF(2). Incidentally, we report here the highest average power ever achieved for a sub-100-fs active Kerr-lens ML Yb-bulk oscillator.

Sub-50 fs, Kerr-lens mode-locked Yb:CaF2 laser oscillator delivering up to 2.7 W

By means of a high-brightness optical pumping scheme with a fiber laser, we demonstrate Kerr-lens mode locking (KLM) with an Yb:CaF2 laser crystal. Stable 48 fs pulses are produced at an average power of 2.7 W.

High power green lasers for gamma source

A high intensity Gamma source is required for Nuclear Spectroscopy, it will be delivered by the interaction between accelerated electron and intense laser beams. Those two interactions lasers are based on a multi-stage amplification scheme that ended with a second harmonics generation to deliver 200 mJ, 5 ps pulses at 515 nm and 100 Hz. A t-Pulse oscillator with slow and fast feedback loop implemented inside the oscillator cavity allows the possibility of synchronization to an optical reference. A temporal jitter of 120 fs rms is achieved, integrated from 10 Hz to 10 MHz. Then a regenerative amplifier, based on Yb:YAG technology, pumped by fiber-coupled QCW laser diodes, delivers pulses up to 30 mJ. The 1 nm bandwidth was compressed to 1.5 ps with a good spatial quality: M2 of 1.1. This amplifier is integrated in a compact sealed housing (750 x 500 x 150 mm), which allows a pulse-pulse stability of 0.1 % rms, and a long-term stability of 1,9 % over 100 hours (with +/-1°C environment). The main amplification stage uses a cryocooled Yb:YAG crystal in an active mirror configuration. The crystal is cooled at 130 K via a compact and low-vibration cryocooler, avoiding any additional phase noise contribution, 340 mJ in a six pass scheme was achieved, with 0.9 of Strehl ratio. The trade off to the gain of a cryogenic amplifier is the bandwidth reduction, however the 1030 nm pulse was compressed to 4.4 ps. As for the regenerative amplifier a long-term stability of 1.9 % over 30 hours was achieved in an environment with +/-1°C temperature fluctuations The compression and Second Harmonics Generation Stages have allowed the conversion of 150 mJ of uncompressed infrared beam into 60 mJ at 515 nm.

Laser-induced damage threshold of Yb:YAG crystals at stretched 150-ps pulses (Conference Presentation)

High power high energy lasers have recently emerged as potential solution for several applications such as secondary rays generation, nuclear fusion and medical therapy. One major limitation of such systems for high energy extraction is the laser-induced damage threshold (LIDT) of laser components. In this context, many studies have been devoted to the determination of the LIDT of laser materials under certain operational conditions and the identification of the limiting factors at the nanoseconds and femto/sub-picoseconds regime 1–3.However, these measurements do not consider that in most high intensity laser chains such as chirped pulsed amplification (CPA), pulses are stretched to larger duration such as hundreds of picoseconds. Thus, measuring the LIDT of laser materials under stretched pulses irradiation becomes critical. In this work, we report a study of the influence of the coating treatment and fatigue in the LIDT of Yb:YAG crystals under stretched pulses by means of 1-on-1, Rasterscan and S-on-1 tests. We use a 1mJ, 1kHz laser (S-Pulse model from Amplitude Systemes) modified to support 150 ps-pulse duration. We show a lower LIDT of the AR-coating compared to that of the HR-coating (7J/cm2) and preliminary outcomes point out a non-deterministic effect of the fatigue at this regime of pulse duration. These results show the importance of testing critical components at hundred-picoseconds regime for high power and high energy lasers. 1. Sozet, M. et al. Laser damage density measurement of optical components in the sub-picosecond regime. 40, 2–5 (2015). 2. Smith, A. V & Do, B. T. Bulk and surface laser damage of silica by picosecond and nanosecond pulses at 1064 nm. (2008). 3. Jensen, L. O. et al. Investigations on SiO 2 / HfO 2 mixtures for nanosecond and femtosecond pulses a Laser. 7842, 1–10 (2017).

Fiber laser pumped Yb:CaF 2 regenerative amplifier delivering 130 fs pulses with 4.3 W output power

High repetition rate femtosecond lasers able to deliver pulse energies ranging from few hundred microjoules to the millijoule level is a very active and competitive field in laser research. In laser bulk technology, major improvements toward high average power were (i) the reduction of the pump heat load through Yb-doped crystals development and (ii) the availability of low cost and bright diode-laser pump sources. Nodaways, Yb:YAG laser sources provide few hundreds of watts at multi-kHz repetition rates in thin disk [1] or slab [2] amplifier configurations with pulse duration close to the picosecond level due to the restricted gain bandwidth of Yb:YAG. Shortening the pulse duration of high average power laser, without the help of self-phase modulation process inside or outside the amplifier, requires Yb-doped crystal hosts associating broad gain bandwidth and good thermal conductivity. So far, Yb-doped regenerative amplifiers delivering multi-watt at multi-kHz repetition rate provide pulse duration close to 300 fs in Yb:CALGO [3] and 200 fs in Yb:CaF2 at cryogenic temperature [4]. In this work, we report on the first 130 fs room temperature Yb:CaF2 chirped pulse regenerative amplifier delivering an average power exceeding 4.3 watts when the laser system operates from 5 kHz to 50 kHz. By means of an Yb-doped fiber pump source, a long Yb:CaF2 crystal with low doping concentration has been used to increase the heat load volume and therefore reduce the amplifier temperature while maintaining high optical efficiency and broad effective bandwidth emission.

High-power sub-50 fs, Kerr-lens mode-locked Yb:CaF2 oscillator pumped by high-brightness fiber- laser

We investigated the influence of the spatial pump beam quality on the generation of ultra-short pulses in high-brightness Yb:fiber laser-pumped pure Kerr-lens mode-locked Yb:CaF2 oscillators. We report pulse duration as short as 48 fs with an average output power of 2.7 W.

Sub 40 fs Kerr-lens mode-locked Yb:CALGO laser oscillator with more than 1 W

We report on Kerr lens mode locking of Yb:CALGO by means of high-brightness optical pumping with a diffraction limited fibre laser. Various cavity configurations have been investigated to deliver sub-40 fs pulses at watt level and pulse duration as short as 32 fs.

Pumping Yb:doped Bulk Materials with 976-nm Fiber Lasers

Advanced Solid State Lasers (ASSL)