François Salin

High-power rod-type photonic crystal fiber laser

We report on a novel ytterbium-doped fiber design that combines the advantages of rod and fiber gain media. The fiber design has outer dimensions of a rod laser, meaning a diameter in the range of a few millimeters and a length of just a few tens of centimeters, and includes two important waveguide structures, one for pump radiation and one for laser radiation. We obtained 120-W output power in single-mode beam quality from a 48-cm-long fiber cane that corresponds to an extracted power of 250 W/m. The fiber has significantly reduced nonlinearity, which therefore allows for scalability in the performance of a high-peak-power fiber laser and amplifier system.

High power ytterbium-doped rod-type three-level photonic crystal fiber laser

In this paper, we investigate power scalability of ytterbium-doped ultra large core photonic crystal fiber laser operating on the zero-line transition. We first report on an 80 microm core diameter ytterbium-doped rod-type photonic crystal fiber laser emitting up to 94 W in continuous wave regime when operating at 977 nm, 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 three-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 977 nm.

Generation of 90-fs pulses from a mode-locked diode-pumped Yb 3+ :Ca 4 GdO(BO 3 ) 3 laser

A diode-pumped Yb>(3+):Ca(4)GdO(BO>(3))(3) (Yb:GdCOB) laser generating 90-fs pulses at a center wavelength of 1045 nm is demonstrated. This is, to our knowledge, the shortest pulse duration obtained from an ytterbium laser with a crystalline host. This laser is mode locked with a high-finesse semiconductor saturable-absorber mirror and emits 40 mW of average power at a repetition rate of 100 MHz.

Photodarkening and photobleaching of an ytterbium-doped silica double-clad LMA fiber

We studied the temporal behaviour of photodarkening in an Yb-doped LMA fiber and show photobleaching of the same fiber. The absorption spectra and the influence on the lasing properties are shown.

Millijoule pulse energy Q-switched short-length fiber laser

We report on a Q-switched short-length fiber laser producing 100 W of average output power at 100 kHz repetition rate and pulse durations as short as 17 ns. Up to 2 mJ of energy and sub-10-ns pulse duration are extracted at lower repetition rates. This performance is obtained by employing a rod-type ytterbium-doped photonic crystal fiber with a 70 microm core as gain medium, allowing for very short pulse durations, high energy storage, and emission of a single-transverse-mode beam.

Compensation of pulse-distortion in saturated laser amplifiers.

We derive an expression describing pre-compensation of pulse-distortion due to saturation effects in short pulse laser-amplifiers. The analytical solution determines the optimum input pulse-shape required to obtain any arbitrary target pulse-shape at the output of the saturated laser-amplifier. The relation is experimentally verified using an all-fiber amplifier chain that is seeded by a directly modulated laser-diode. The method will prove useful in applications of high power, high energy laser-amplifier systems that need particular pulse-shapes to be efficient, e.g. micromachining and scientific laser-matter-interactions.

High-power picosecond fiber amplifier based on nonlinear spectral compression

We report on the rare-earth-doped fiber-based generation of nearly transform-limited 10-ps pulses based on self-phase-modulation-induced spectral compression. An ytterbium-doped low nonlinearity photonic crystal fiber is used as a gain medium. An average power of as much as 97 W at a repetition rate of 47 MHz, corresponding to a peak power as high as 200 kW, was obtained. Furthermore, efficient second-harmonic generation by application of this high-power laser source is discussed.

Ultra-broad bandwidth parametric amplification at degeneracy

We report on a novel approach of ultra-broad bandwidth parametric amplification around degeneracy. A bandwidth of up to 400 nm centered around 800 nm is amplified in a BBO crystal by using chirped pump pulses with a bandwitdth as broad as 10 nm. A supercontinuum signal is generated in a microstructured fiber, having to first order a quadratic chirp, which is necessary to ensure temporal overlap of the interacting waves over this broad bandwidth. Furthermore, we discuss the potential of this approach for an octave-spanning parametric amplification.

Inner cladding microstructuration based on symmetry reduction for improvement of singlemode robustness in VLMA fiber

Very large mode area, active optical fibers with a low high order mode content in the actively doped core region were designed by removing the inner cladding symmetry. The relevance of the numerical approach is demonstrated here by the investigation of a standard air-silica Large Pitch Fiber, used as a reference. A detailed study of all-solid structures is also performed. Finally, we propose new kinds of geometry for 50 μm core, all-solid microstructured fibers enabling a robust singlemode laser emission from 400 nm to 2200 nm.

Portable, tunable, high-luminosity spherical crystal spectrometer with an x-ray charge coupled device, for high-resolution x-ray spectromicroscopy of clusters heated by femtosecond laser pulses

A portable (200×100×100 mm3), high-luminosity, spherically bent crystal spectrometer was designed for measuring in a wide spectral range of 1.2–19.6 A very low emissivity x-ray spectra of different clusters heated by 35 fs laser radiation. This spectrometer is associated with a custom design x-ray charge coupled device that features a large sensitive area (24.6×24.6 mm2) and a small pixel size (24×24 μm2). This apparatus provides simultaneous high spectral (λ/δλ∼1000–5000) and spatial (40–80 μm) resolution. A large (30×10 mm2) open aperture mica crystal with R=100 mm is used as the dispersive and focusing element. The large tuneability of the spectrometer makes it possible to record high-resolution spectra of H-like ions of oxygen (CO2 clusters) in a spectral range of 15–17 A, Ne-like like ions of Kr in a spectral range of 5–5.7 A, and He-like spectra of Ar in a spectral range of 3.0–3.4 and 3.7–4.4 A without any adjustment of the spectrometer setup. Thanks to the high luminosity (high collection efficien...