Johan Boullet

Generation of high energy and high quality ultrashort pulses in moderately non-linear Fiber Chirped Pulse Amplifier

We report the generation of high temporal quality high energy ultra-short pulses from a moderately non-linear fiber chirped pulse amplifier. The system is based on a two amplification stages and delivers 270 fs pulses of 100 μJ energy at a repetition rate of 300 kHz. The excellent temporal quality of the recompressed pulses, down to 1.1 the Fourier limit, allows the production of ~ 340 MW of peak power. The fibre chirped pulse amplifier is design to compensate the nonlinear phase shift accumulated throughout the amplifier stages by third order of dispersion provided by mismatched temporal stretcher and compressor units.

Laser surface texturization for high power cladding light stripper

We demonstrated herein a new type of cladding light strippers suitable for high power systems. By precisely micro-machining the surface of the fiber we create CLS with efficiencies as high as 97 % for large NA, multi-mode, cladding light (NA = 0.3), and 70 % for single-mode, low NA, light. The NA of the cladding light is reduced from 0.3 down to 0.08. The CLS exhibit a 1°C/stripped-Watt temperature elevation making them very suitable for high power applications. This fabrication method is simple and reliable. We have tested different texturization geometries on several different fibers: 20/400 from Nufern, KAGOME, and LMA 10 and LMA 15 fibers (results not shown herein) and we observed good efficiencies and temperature elevation behavior for all of them. Finally, large scale production of CLS with this method is possible since the time necessary to prepare on CLS is very small, in the order of few seconds.

Photodarkening kinetics in a high-power YDFA versus CW or short-pulse seed conditions

We propose an innovating model to describe the kinetics of competing photo-darkening and photo-bleaching phenomena in high-power, Ytterbium-Doped-Fibre-Amplifiers. This model makes use of aggregated species of trivalent Ytterbium and divalent ions, which operate as primarily efficient color-centers. This ensures multi-photon excitation, partly from the pump and partly from the signal. The fit of numerical computations with dedicated experiments help to validate our theoretical assumptions, in the definition of the involved physics. Potential applications of this study include further discussions for the selection of processing options with fibre-manufacturers and the optimization of operating conditions.

Multi-100W class, fully integrated, monolithic ytterbium-doped photonic-crystal fiber amplifier module

We report a high performance, fully monolithic 40 μm core, Yb-doped photonic crystal fiber amplifier module. The developed fused combiner allows us to couple 6 pumps of 50 W at 976 nm and 5 W of signal at 1064 nm in the PCF amplifier. We then produced up to 210 W of average power at 1064 nm which is the highest power ever delivered by a fully monolithic PCF amplifier. The module is entirely thermally controlled in a rugged package, and has run more than 25 days at > 100W average power with an excellent peak to peak power stability < 1%.

Yb-doped fiber laser system generating 12-ns 0.7-mJ pulses at 82 kHz at 977 nm

We demonstrate an Ytterbium-doped fiber laser system generating high energy pulses at the non-conventional wavelength of 977 nm. An actively Q-switched master fiber oscillator delivers 1.2 W of average power in 12 ns pulses at 82 kHz of repetition rate. This pulsed fiber source is then amplified in an ultra-large core photonic crystal fiber amplifier up to 71 W. Deducing the fraction of power contained in interpulse ASE, we obtained 0.7 mJ pulses at 977 nm, resulting in a pulse peak-power of >55 kW. To the best to our knowledge, this system delivers the highest performances ever demonstrated in this spectral window.

94-W ytterbium-doped single-mode rod-type photonic crystal fiber operating at 977 nm

In this contribution, we report on an 80-μm core diameter Yb-doped rod type photonic crystal fiber laser emitting up to 94W in CW regime when operating at 977nm, which is to our knowledge the highest output power ever achieved from a single-mode solid-state laser operating at this wavelength. Key parameters of ytterbium doped 3-level laser, such as transparency pump intensity, pump absorption saturation, and gain competition between three and four level laser operation are then discussed in the particular context of high power fiber laser operating at 977nm. Possible applications of the demonstrated source are then discussed.

Regime dependence of photo-darkening-induced modal degradation in high power fiber amplifier (Conference Presentation)

Thermally induced transverse modal instabilities (TMI) have attracted these five years an intense research efforts of the entire fiber laser development community, as it represents the current most limiting effect of further power scaling of high power fiber laser. Anyway, since 2014, a few publications point out a new limiting thermal effect: fiber modal degradation (FMD). It is characterized by a power rollover and simultaneous increase of the cladding light at an average power far from the TMI threshold together with a degraded beam which does not exhibit temporal fluctuations, which is one of the main characteristic of TMI. We report here on the first systemic experimental study of FMD in a high power photonic crystal fiber. We put a particular emphasis on the dependence of its average power threshold on the regime of operation. We experimentally demonstrate that this dependence is intrinsically linked to regime-dependent PD-saturated losses, which are nearly three times higher in CW regime than in short pulse picosecond regime. We make the hypothesis that the existence of these different PD equilibrium states between CW regime and picosecond QCW pulsed regime is due to a partial photo-bleaching of color centers in picosecond regime thanks to a higher probability of multi-photon process induced photobleaching (PB) at high peak power. This hypothesis is corroborated by the demonstration of the reversibility of the FMD induced in CW regime by simply switching the seed CW 1064 nm light by a short pulse, picosecond oscillator.

Single frequency, ultra-low noise, CW, 4W 488nm fiber laser

We have recently developed an industrial laser platform emitting in the non-conventional range around 976 nm. This 15 W continuous wave spatially single mode linearly polarized fiber laser can be forced to work in narrow line width or single frequency configuration. Its frequency doubling at 488 nm can be used to replace argon gas laser technology in many applications. We have studied the second harmonic generation of our source to verify its suitability with several industrial application needs in terms of efficiency, temporal stability and noise level.

High order harmonic generation at ultra high repetition rate from ytterbium doped fiber chirped pulse amplification

We report on the first experimental demonstration of high order harmonic generation in rare gases directly from a high power Ytterbium doped fiber chirped pulse amplification system. The laser delivers 270 fs pulses in the 30-100 μJ energy range at repetition rate varying from 100 kHz to 1 MHz. A proper focalization allows reaching several 1013W/cm2 in the gas jet. We have been able to produce and detect harmonics up to order 31 in Ar, Kr, and Xe at 100kHz repetition rate. Harmonic generation at 1 MHz is also demonstrated in Xe up to harmonic 15.