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We report on mid-infrared supercontinuum generation from 4 to 9 µm in orientation- patterned gallium-arsenide waveguides pumped by nanojoule-class ultrafast fiber lasers.

We report on the first laser operation of a disordered Tm:CaGdAlO4 crystal on the 3H4 → 3H5 transition. Under direct pumping at 0.79 µm, it generates 264 mW at 2.32 µm with a slope efficiency of 13.9% and 22.5% vs. incident and absorbed pump power, respectively, and a linear polarization (σ). Two strategies to overcome the bottleneck effect of the metastable 3F4 Tm3+ state leading to the ground-state bleaching are exploited: cascade lasing on the 3H4 → 3H5 and 3F4 → 3H6 transitions and dual-wavelength pumping at 0.79 and 1.05 µm combining the direct and upconversion pumping schemes. The cascade Tm-laser generates a maximum output power of 585 mW at 1.77 µm (3F4 → 3H6) and 2.32 µm (3H4 → 3H5) with a higher slope efficiency of 28.3% and a lower laser threshold of 1.43 W, out of which 332 mW are achieved at 2.32 µm. Under dual-wavelength pumping, further power scaling to 357 mW at at 2.32 µm is observed at the expense of increased laser threshold. To support the upconversion pumping experiment, excited-state absorption spectra of Tm3+ ions for the 3F4 → 3F2,3 and 3F4 → 3H4 transitions are measured for polarized light. Tm3+ ions in CaGdAlO4 exhibit broadband emission at 2.3 - 2.5 µm making this crystal promising for ultrashort pulse generation.

We report on a bulk thulium laser operating on the 3H4 → 3H5 transition with pure upconversion pumping at 1064 nm by an ytterbium fiber laser (addressing the 3F4 → 3F2,3 excited-state absorption (ESA) transition of Tm3+ ions) generating 433 mW at 2291 nm with a slope efficiency of 7.4% / 33.2% vs. the incident / absorbed pump power, respectively, and linear laser polarization representing the highest output power ever extracted from any bulk 2.3 µm thulium laser with upconversion pumping. As a gain material, a Tm3+-doped potassium lutetium double tungstate crystal is employed. The polarized ESA spectra of this material in the near-infrared are measured by the pump-probe method. The possible benefits of dual-wavelength pumping at 0.79 and 1.06 µm are also explored, indicating a positive effect of co-pumping at 0.79 µm on reducing the threshold pump power for upconversion pumping.

Driven by many applications in a wide span of scientific fields, a myriad of advanced ultrafast imaging techniques have emerged in the last decade, featuring record-high imaging speeds above a trillion-frame-per-second with long sequence depths. Although bringing remarkable insights into various ultrafast phenomena, their application out of a laboratory environment is however limited in most cases, either by the cost, complexity of the operation or by heavy data processing. We then report a versatile single-shot imaging technique combining sequentially timed all-optical mapping photography (STAMP) with acousto-optics programmable dispersive filtering (AOPDF) and digital in-line holography (DIH). On the one hand, a high degree of simplicity is reached through the AOPDF, which enables full control over the acquisition parameters via an electrically driven phase and amplitude spectro-temporal tailoring of the imaging pulses. Here, contrary to most single-shot techniques, the frame rate, exposure time, and frame intensities can be independently adjusted in a wide range of pulse durations and chirp values without resorting to complex shaping stages, making the system remarkably agile and user-friendly. On the other hand, the use of DIH, which does not require any reference beam, allows to achieve an even higher technical simplicity by allowing its lensless operation but also for reconstructing the object on a wide depth of field, contrary to classical techniques that only provide images in a single plane. The imaging speed of the system as well as its flexibility are demonstrated by visualizing ultrashort events on both the picosecond and nanosecond timescales. The virtues and limitations as well as the potential improvements of this on-demand ultrafast imaging method are critically discussed.

Spectroscopy and mid-infrared laser operation of Er3+-doped low-phonon-energy fluorite- type crystals, MF2 (M = Ca, Sr, Ba, Ca/Sr and Ba/Sr) were studied. The Er3+:CaF2 laser generated 702 mW at 2.80 μm with a 37.9% slope efficiency.

Excited-state absorption of Tm3+ ions (3F4→3F2,3 and 3H4) in the KLu(WO4)2 crystal is studied. Mid-infrared laser operation (3H4→3H5) is achieved with this crystal under upconversion pumping at 1.06 μm yielding 433 mW at 2291 nm. © 2022 The Author(s)

Transparent ceramics based on “mixed” sesquioxides, Er:(Y,Sc)2O3, are fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. They exhibit inhomogeneously broadened spectral bands. A continuous-wave Er:(Y,Sc)2O3 ceramic laser generates 312 mW at 2716 nm.

Cascade lasing in a Tm:CALGO crystal at 1.8 µm (3F4→3H6) and 2.3 μm (3H4→3H5) is demonstrated with the originality of lacking a competition between the two laser channels, owing to dual-wavelength (direct and upconversion) pumping.

We report on the first, to our knowledge, mid-infrared laser operation of two Er3+-doped barium-containing fluorite-type crystals, BaF2 and (Sr,Ba)F2, featuring a low-phonon energy behavior. A continuous wave 4.9 at.% Er:(Sr,Ba)F2 laser generated 519 mW at 2.79 µm with a slope efficiency of 25.0% and a laser threshold of 27 mW. The vibronic and spectroscopic properties of these crystals are determined. The phonon energy of (Sr,Ba)F2 is as low as 267 cm−1. The Er3+ ions in this crystal feature a broadband emission owing to the 4I11/2 → 4I13/2 transition and a long luminescence lifetime of the 4I11/2 level (10.6 ms) making this compound promising for low-threshold, broadly tunable, and pulsed 2.8-µm lasers.

Picosecond duration terahertz pulses are suitable for many applications and, recently, their ability to trigger electron emission from nanometric samples has been demonstrated [1] , [2] . The development of similar approaches to drive ions emission is very prone to open new application areas notably for matter analysis and manipulation. Field emission of positive ions from a nanometric tip (called field evaporation) is the basic principle of the Atom Probe Tomography (APT), which is a 3D imaging technique based on controlled field evaporation of atoms from a nanometric needle shaped sample under a strong electric field [3] .

High-power wavelength-agile fiber sources are now competitive for many widespread applications such as non-linear imaging or coherent Raman scattering spectroscopy. Soliton self-frequency shift, self-mode conversion and self-phase modulation are commonly used to obtain the necessary wavelength shift but are limited in peak-power scalability due to intensity-related damages. However, it is possible to overcome this limitation by exploiting the broad tunability offered by degenerate four-wave mixing in optical fibers along with chirped-pulse amplification (CPA), then allowing the generation of high-energy fs pulses at different wavelengths [1] - [4] . Moreover, the exploitation of this principle in a fiber optical parametric oscillator (FOPO) with normal dispersion can enable record performances in terms of pulse energy [5] . Combining both concepts to build a fiber optical parametric chirped-pulse oscillator (FOPCPO) is then attractive to enable a full control of the output wavelength and bandwidth, as recently shown in a numerical study [6] . Thereby, we experimentally demonstrate here a high-energy FOPCPO, numerically analyze its operation, and discuss its potential for further energy scaling [7] .

The recent emergence of real-time temporal and spectral characterization techniques such as time lenses [1] and dispersive Fourier transformation (DFT) [2] has opened new horizons by unveiling the shot-to-shot dynamics of ultrafast optical systems. Especially, the ability of DFT to record large ensembles of single-shot spectra has enabled the use of statistical metrics to describe the dynamical behaviours of various optical phenomena. In this frame, spectral correlations have been used for understanding the complex processes involved in supercontinuum generation, modulation instability, four-wave mixing or random lasing. The shaping of spectral correlations has been experimentally demonstrated in fiber systems [3] , [4] and could now drive many quantum optics applications. However, to date, such wavelengths correlations have never been studied within fiber optical parametric oscillators (FOPO), which are now mature and widespread wavelength-agile sources.

Mid-infrared coherent light sources are of great interest for numerous applications ranging from spectroscopy, biomedicine and surgery, material processing, defense and security, as this spectral region contains the signatures of most basic molecules’ vibrations. Most of these applications require ultrafast lasers to avoid thermal effects e.g. in material processing and surgery or to optimize nonlinear processes, such as those involved in mid-IR supercontinuum generation. In recent years, considerable efforts have been directed towards the development of compact ultrafast sources based on rare earth doped fluoride-zirconate (ZBLAN) fibers. The best performances are obtained using ZBLAN fibers pumped with high power laser diodes around 980 or 1150 nm using, respectively, the 2.8 µm transition from the 4 I 11/2 to the 4 I 13/2 energy levels of erbium ions [1] or the 2.9 µm transition ( 5 I 6 → 5 I 7 ) of holmium-doped ZBLAN fibers [2] . A pulse energy as high as 7.6 nJ with 180 fs pulse duration and 37 kW peak power was then demonstrated [2] . However, these sources are based on the nonlinear polarization evolution technique which is highly sensitive to thermal or mechanical perturbation in its environment. The use of real saturable absorbers to initiate and stabilize the mode-locking regime allows to reduce this sensitivity to the environment in the picosecond regime [3] . Nonetheless, such sources deliver output beams with a highly unstable polarization state, which varies along with the perturbations. Here, we then report on the first demonstration of a passively mode-locked oscillator featuring a polarization maintaining erbium-doped ZBLAN fiber.

Practical realization of stable and high brightness sources of ultra-short electron pulses is an important issue in the development of time-resolved electron microscopy for the study of ultra-fast dynamics in materials. Here, we report on the experimental investigation of static (in the dark) and pulsed (under illumination by sub-picosecond laser pulses at 1040 nm) electron emission from single-crystal diamond needles. A significant increase of electron emission current was detected under laser illumination. The nonlinear dependence of the emission current on the laser intensity and on the angle between the needle and the laser beam polarization axis suggests multi-photon emission processes. This interpretation is in agreement with electron spectroscopy measurements performed for electrons emitted at different bias voltages and different laser power levels and repetition rates. The remarkable feature of the diamond emitters is their stability under high average power of laser radiation. This provides a new highly efficient source of photoemitted electrons based on single-crystal diamond.

We report on the design of OP-GaAs rib waveguides for frequency conversion in the mid-infrared and explore their performances for parametric generation. The samples used are between 10 and 25 mm long and exhibit quasi-phasematched (QPM) periods from 85 to 100 μm. The waveguides are pumped by a femtosecond erbium-doped fluoride fiber laser combined with a soliton self-frequency shift converter delivering sub-300 fs pulses at a wavelength tunable between 2.8 and 3.3 μm. By adjusting the pump wavelength, our OP-GaAs platform can produce ultrashort pulses widely tunable around 4 and 12 μm for the signal and idler, respectively. These results fit quite well our calculations of QPM curves.

Driven by many applications in a wide span of scientific fields, a myriad of advanced ultrafastimaging techniques have emerged in the last decade, featuring record-high imaging speeds abovea trillion-frame-per-second with long sequence depths. Although bringing remarkable insights invarious ultrafast phenomena, their application out of a laboratory environment is however limitedin most cases, either by the cost, complexity of operation or by an heavy data processing. We thenreport a flexible single-shot imaging technique combining sequentially-timed all-optical mappingphotography (STAMP) with acousto-optics programmable dispersive filtering. The full controlover the acquisition parameters is enabled via the spectro-temporal tailoring of the imaging pulsesin an electrically-driven spectral phase and amplitude shaper in which the pulse shaping in boththe temporal and spectral domains is controlled through the interaction of the light field with anacoustic wave. Here, contrary to most single-shot techniques, the frame rate, exposure time and frameintensities can be independently adjusted in a wide range of pulse durations and chirp values, makingthe system remarkably versatile and user-friendly. The imaging speed of the system as well as itsflexibility are validated by visualizing ultrashort events on both the picosecond and nanosecond timescales. With the perspective of real-world applications and to achieve the highest technical simplicity,we eventually demonstrate its lensless operation based on digital in-line holography. The virtues andlimitations as well as the potential improvements of this on-demand ultrafast imaging method arecritically discussed.

We report a MOPA laser system near 910nm employing Nd-doped PM-fibers and a SESAM for mode-locking. SPM-induced spectral broadening in a W-type Nd-doped fiber amplifier allows pulse recompression to 300fs and pulse energy of 11nJ.

This Letter presents the efficient laser operation of a

International audience; Yttrium orthoaluminate (YAlO3) is an attractive laser host crystal for doping with thulium (Tm3+) ions. We report on the absorption and stimulated-emission (SE) cross-sections of this orthorhombic (sp. gr. Pnma) Tm:YAlO3 crystal for the principal light polarizations, E || a, b and c. Polarized absorption data lead to the Judd-Ofelt parameters Ω2 = 1.46, Ω4 = 2.82 and Ω6 = 1.09 [10-20 cm2]. In particular, for the 3H4 → 3H5 transition, it is found a stimulated emission cross section of 0.86×10-20 cm2 at 2278 nm corresponding to an emission bandwidth of ~12 nm (for E || b). Continuous-wave laser operation on this 3H4 → 3H5 transition is achieved with an 1.8 at.% Tm:YAlO3 crystal under laser-pumping at 776 nm. The mid-infrared Tm:YAlO3 laser generated 0.96 W at ~2274 nm with a slope efficiency of 61.8% and a linear laser polarization (E || b). Tm:YAlO3 is promising for mode-locked lasers at ~2.3 μm.

We report on Czochralski growth, detailed ground- and excited-state absorption and emission spectroscopy and highly-efficient mid-infrared (∼2.3 µm) laser operation of a cubic potassium yttrium fluoride crystal, Tm:KY

A Tm: KY3F10 laser operating on the 3H4 →3H5 transition (2340 nm) is mode-locked by a semiconductor saturable absorber mirror. A strong etalon effect originating from the SESAM is observed limiting the pulse duration to ~100 ps.

We report on mid-infrared optical parametric generation in the 4–5 μm and 9–12 μm bands by pumping custom-designed orientation-patterned gallium arsenide (OP-GaAs) rib waveguides with an ultrafast femtosecond fiber laser system. This pump source is seeded by a mode-locked fluoride fiber laser with 59 MHz repetition rate and can be tuned between 2.8 and 3.2 μm using a soliton self-frequency shifting stage. The single TE and TM modes OP-GaAs crystals feature quasi-phase-matched grating periods of 85 and 90 μm and different transverse sizes thus allowing a wide spectral tunability.

Fluorite-type 5 at.% Er3+:(M1,M2)F2 (M1 = Ca, Ba; M2 = Sr) crystals were grown by the conventional Bridgman technique and a comparative study of their spectroscopic properties was performed. The vibronic properties of the fluorite-type crystals were studied by Raman spectroscopy. The Er:(M1,M2)F2 crystals exhibited a slightly inhomogeneous broadening of mid-infrared luminescence spectra as compared to the ‘parent’ compound, Er:SrF2. The luminescence lifetimes of the 4I11/2 and 4I13/2 manifolds were measured, e.g., for the Er:(Ca,Sr)F2 crystal, the luminescence lifetimes were estimated to be 8.64 ms and 5.64 ms, respectively, representing a favorable ratio for mid-IR laser operation.

We report on a diode-pumped Tm:LiYF4 laser operating on the 3H4 → 3H5 transition (at ∼ 2 . 3 μ m) passively Q-switched by a Cr2＋:ZnSe saturable absorber. This laser delivers a maximum average output power of 130 mW at 2304.6 nm with a nearly diffraction limited beam, a linear polarization ( π ) and no colasing at ∼ 1 . 9 μ m. The corresponding pulse characteristics (duration/energy) are 1.24 μ s/3.6 μ J at a repetition rate of 36 kHz. By power scaling under quasi-CW pumping, even shorter pulse durations of 870 ns and higher pulse energies of 6.1 μ J are achieved. The performance of the laser is simulated using a model of a quasi-four-level gain medium and a “slow” saturable absorber showing a good agreement with the experiment. The effect of the thermal lens of the saturable absorber on the pulse characteristics is discussed.

We report on the successful operation of a dissipative soliton fiber laser mode-locked with a bulk InGaAs-based saturable absorber mirror forming a resonant micro-cavity. Highly-chirped pulses with several nanojoules of energy are thus produced. Remarkably, the laser performances in terms of output power and amplitude stability are comparable to those obtained with their multiple-quantum-well-based counterparts. This letter suggests that this simplified approach for saturable absorber mirrors can be considered as a promising alternative regarding ultrafast optics applications.

The orthorhombic Tm

We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm

High-brightness and tunable lasers operating in the 1800–2000 nm wavelength region are very attractive for applications such as spectroscopy, atmospheric remote sensing and medical surgery. So far, Tm3+-doped crystalline hosts, such as YLF and YAG, have proven to be ones of the most interesting gain materials [1, 2]. Among other available hosts, Tm:CaF 2 offers a high thermal conductivity and a very broad emission bands due to multisite crystal structure. Therefore, Tm:CaF 2 is a good candidate for high-power and broadband tunable laser emission between 1750 nm and 2000 nm. However, there are only a few reports on Tm:CaF 2 laser operation, mainly because of the lack of powerful pump sources at the optimum absorption wavelength of 767 nm, when using cross-relaxation process [3]. In comparison, in-band pumping of Tm-doped materials can be very efficient as the quantum defect may approach 85% [4, 5].

International audience; We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm3+:LiYF4/LiYF4 epitaxies via diamond-saw dicing. They are pumped by a RFL based on an erbium master oscillator power amplifier and a GeO2-doped silica fiber and emit polarized output at 1679 nm. A CW in-band-pumped (H63→F43) Tm3+:LiYF4 WG laser generates up to 2.05 W of a linearly polarized single-transverse-mode output at 1881 nm with a slope efficiency of 78.3% and a laser threshold of only 12 mW (versus the absorbed pump power).

Quasi-continuous-wave laser operation of 20 at.% Tm:LiYF

International audience

Novel upconversion pumping schemes based on excited-state absorption (ESA) and photon avalanche are proposed for 2.3 μm (3H4→3H5) Thulium lasers. Low-threshold Tm3+:LiYF4 laser pumped at 1040 nm generates 102 mW at 2302 nm.

We demonstrate a fiber optical parametric chirped-pulse oscillator (FOPCPO) pumped in the normal-dispersion regime by chirped pulses at 1.036 µm. Highly chirped idler pulses tunable from 1210 nm to 1270 nm with energies higher than 250 nJ are generated from our system, along with signal pulses tunable from 870 nm to 910 nm. Numerical simulations demonstrate that further energy scaling is possible and paves the way for the use of such FOPCPOs for applications requiring high-energy, compact, and low-noise sources, such as in biophotonics or spectroscopy.

Low-loss surface channel waveguides with a cross-section of 30 × 30 μm

The first holmium fluoride waveguide laser, to the best of our knowledge, is reported using a 25-μm-thick Gd

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The 3H4→3H5 transition of Tm3+ in LiYF4 is characterized. Efficient 2.3-μm bulk and waveguide lasers are demonstrated. A CW diamond-saw-diced channel waveguide laser generated 147 mW at 2306 nm with a slope efficiency of 33.5%.

The first Holmium fluoride waveguide laser is reported using a 25-^m-thick Tm,Ho:LiYF4 layer grown by liquid phase epitaxy. Pumped at 797.2 nm, it generates 81 mW at 2051 nm with a slope efficiency of 24%.

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A passively mode-locked Tm:YLF laser emitting at 2.3 μm is reported for the first time, to the best of our knowledge. The continuous-wave stable mode-locking operation is obtained with a semiconductor saturable absorber mirror at a repetition rate of 100 MHz. The average output power is 165 mW for a pulse duration of 94 ps.

The development of high energy short pulse sources at 2 μm wavelength range demonstrates a steady progress during recent years. Real world applications such as medical surgery and polymer micromachining [1] require compact, monolithically integrated all-fibered configurations. While table-top systems deliver outstanding performances on the order of hundreds of μJ and 2 GW peak power in 200 fs compressed pulses [2], the few μJ level is still a hurdle for monolithic all-fiber systems. The best results obtained in relatively compact systems are achieved using thulium-doped fiber master oscillator power amplifier (MOPA) systems operating at center wavelengths around 2 μm to avoid water vapor absorption in the air near the optimal 1.9 μm regime of thulium. Several microjoules of energy with sub-picosecond pulses were achieved with such configurations [3] [4]. In this communication, we present a 10 μJ-class ultrafast thulium-doped fiber MOPA system operating at 1940 nm. The chirped pulse amplification (CPA) approach was applied for the seed pulses directly generated at the operating wavelength of 1940 nm. Our main oscillator is working in the dissipative soliton (normal dispersion) regime [5]. This concept allows all-fibre integration [6] and offers several advantages such as i) high seed average power, ii) adjustable broad spectrum to fit dispersive components transmission band and iii) pre-stretched pulse. To make the total system compact, free-space elements must be avoided. This architecture requires the use of step-index large mode area (LMA) active fibres in the power amplifier stage instead of rod-type photonic crystal fibers. Therefore, the final stage in our MOPA scheme (amplifier N 2 in Fig.1a) is based on highly doped thulium doped fibre featuring 25-micron core diameter. In order to boost the pulse energy above the μJ level, the nonlinear threshold, imposed by active fibre core size, is increased by stretching the seed pulse to 550 ps by means of a chirped fiber Bragg grating (CFBG) stretcher. The system also includes fiberized acousto-optical modulator for repetition rate control. Finally, the output pulse was compressed using chirped volume Bragg grating (CVBG). The linear amplification regime was preserved up to the maximum available pump power where output average power reached P out = 2.4 W at a repetition rate of 100 kHz (Figure 1b, bottom x-axis, left y-axis). After compression with 80 % efficiency this corresponds to P compressed = 1.9 W. The AC trace for maximum achieved performance is presented in Figure 1b (top x-axis, right y-axis). The careful evaluation of the energy concentrated in the central part of the pulse (∼54%) led to a pulse energy E p = 10.3 μJ and to a peak power of 5.1 MW in 2 ps pulses (slightly higher than the Fourier limit of 1.6 ps). Corresponding optical spectrum is presented in Figure 1c (black) together with that measured directly at the amplifier output (red).

A passively mode-locked Tm:YLF laser at 2.3µm is reported for the first time. The sustained mode locking operation is obtained with a SESAM and leads to an average output power of 70 mW with a repetition rate of 100 MHz.

Solitonic effects, including multi-solitonic fission and subsequent self-frequency shift, are used to tailor ultrashort (sub-100 fs) pulses with carrier wavelength broadly tunable in spectral regions between fixed laser lines. Although high-energy pulses can be obtained in stiff waveguides, the benefit of pulse delivery through bends is lost. Here, we report on the generation, sustained propagation, and large frequency shift of megawatt-class pulses in all-silica antiresonant fibers with ultra-large mode area. We designed and fabricated a flexible fiber with a 2710 μm2 effective mode area and a 10 cm critical bend radius. When pumped by a sub-picosecond thulium-doped fiber-based chirped pulse amplifier, the fiber delivers 90 fs pulses at 2220 nm with a 2.8 MW peak power. The system might be used to drive high-order harmonic generation in solids.

Laser operation at 2 µm is reported using an epitaxial, highly Tm-doped, 240 µm thick LiYF4 layer grown by liquid phase epitaxy. Simulation of laser operation is compared to experiments.

We report on a monolithically integrated high repetition rate all-fiber format femtosecond laser operating at 1650 nm. We explore its potential for biological microscopy by imaging mouse brain tissue.

International audience; We report on a mode-locked all-normal dispersion fiber laser featuring a large-mode-area all-solid photonic bandgap fiber. The self-starting chirped-pulse laser delivers 660 mW of average power at a repetition rate of 30 MHz, leading to 22 nJ energy. The output pulses are dechirped outside the cavity to nearly transform-limited duration of 50 fs. Numerical simulations are in good agreement with experiments and highlight the key role of passive spectral filtering on pulse shaping.

Introduction Les kystes colloides du troisieme ventricule sont des tumeurs rares, dont la taille varie generalement de quelques millimetres a 3 cm. Ils se manifestent souvent par des signes d’hypertension intracrânienne par obstruction du foramen de Monro, mais leur risque majeur reste la mort subite. On se propose d’etudier les caracteristiques cliniques, radiologiques et les modalites therapeutiques de cette tumeur a partir d’un cas et d’une revue de la litterature. Materiel et methodes Nous rapportons le cas d’un patient âge de 65 ans sans antecedents pathologiques admis dans un tableau d’hypertension intracrânienne evoluant depuis 1 mois et dont l’exploration radiologique a montre un enorme processus expansif intracrânien au niveau du 3e ventricule faisant 5,7 cm de grand axe associe a une dilatation ventriculaire. L’etude anatomopathologique apres exerese chirurgicale complete a conclu a un kyste colloide. Discussion Les kystes colloides du 3e ventricule sont rares et constituent 0,5 a 1 % des tumeurs cerebrales. La plupart des cas surviennent entre la 3e et la 5e decades. Ils font generalement quelques millimetres a 3 cm de diametre. Ils depassent rarement les 4 cm. Vu leur localisation anatomique, les kystes colloides du troisieme ventricule se manifestent souvent par un tableau d’hydrocephalie d’evolution plus ou moins rapide, voire paroxystique. Cette evolution intermittente et paroxystique est due a l’occlusion intermittente des voies d’ecoulement du liquide cephalorachidien au niveau des foramen interventriculaires. Les troubles de la marche peuvent etre isoles, mais sont souvent associes a un tableau d’hydrocephalie a pression normale. Mais, c’est la mort subite qui constitue la gravite des kystes colloides du V3 et dont le mecanisme serait en rapport avec un blocage ventriculaire ou la compression des centres. Une prise en charge therapeutique rapide, voire urgente, s’impose des lors que le kyste est symptomatique. Parfois, le kyste reste longtemps asymptomatique, et de simples cephalees peuvent etre retrouvees a l’interrogatoire. C’est ce qui expliquerait la taille parfois volumineuse de ces lesions. Le traitement est chirurgical. Mais parfois, l’abstention peut etre discutee. Conclusion Les kystes colloides sont les principales lesions du 3e ventriculaire. Ils ont souvent un aspect clinique et radiologique typique meme si des cas atypiques peuvent survenir. Les voies transcalleuse et transcorticale transventriculaire sont indiquees pour les lesions calcifiees, a contenu solide ou de grande taille.

In this article, we discuss recent advances in ultra-short pulse generation with ytterbium-doped fiber lasers. We discuss the fundamental properties and technical challenges of mode-locked single-mode fiber lasers operating in the 1-μm range, and the methods to achieve high peak-powers. We demonstrate a high-power passively mode-locked fiber laser based on a photonic crystal fiber featuring large-mode-core and short absorption length that greatly exceed the power limitation of single-mode fiber oscillators. Multi-watts average powers in sub-picosecond pulses are obtained. This open new avenue to new performance levels of ultra-short pulse solid-state lasers.