Cesar Jauregui

..6 W of mid-IR radiation at 2570 nm were generated simultaneously with 14.4 W at 672 nm. These power levels of picosecond red radiation are among the highest reported so far for a diffraction limited beam quality in this wavelength region...

..Consequently new analytical formulas for the Raman threshold are obtained and their accuracy is tested. Using these new formulas, the dependence of the Raman threshold on various parameters is studied...

..According to the model presented in this paper, the most likely cause for the beam quality degradation is an inversion-induced grating created by the interplay between modal interference along the fiber and transversal hole burning...

..The relevance of such gratings in the context of the recently observed mode instabilities of high-power fiber laser systems is discussed...

..In a chirped-pulse amplification system we extracted up to 303 W of average power from this fiber with a measured M2 value of 1.4...

..Although the physical origin of this effect is not yet fully understood, we discuss possible explanations. Accordingly, several solutions are proposed in this paper to raise the threshold of this effect...

..CARS spectroscopy and microscopy is demonstrated, probing different molecular vibrational modes within the accessible region between 1200cm(-1) and 3800cm(-1)...

..It is pointed out that an inappropriate choice of pump core diameter, bending radius and/or index depression may lead to avoided crossings that manifest themselves in unwanted deformations of the output beam...

..This work marks a significant step towards a simple and powerful all-fiber, maintenance-free multiplex-CARS source for real-world applications outside a laboratory environment...

..Compared to previous active large-mode area designs, the threshold of mode instabilities is increased by a factor of about 3...

..Finally, it is experimentally shown that the larger the mode-field area, the slower the mode-instability fluctuation is. The observations support the thermal origin of mode instabilities...

..As a proof of principle, we filter azimuthally polarized light in a commercially available fiber in which a fiber Bragg grating has been written by a femtosecond pulsed laser...

..As it is discussed in the paper, this description of mode instabilities can explain many of the experimental observations reported to date...

..Furthermore, the strength of the actual index change is experimentally estimated, and its use to overcome avoided crossings is discussed and experimentally demonstrated...

..This record performance is enabled by a large-pitch fiber with a core diameter of 135 µm. This fiber allows for effective single-mode operation with mode field diameters larger than 90 µm even at average output powers exceeding 100 W...

..These measurements confirm that energy transfer between the fluctuating transversal modes takes place in millisecond-time-scale...

..It is shown that a pentagonal design can increase the mode discrimination and, simultaneously, also improve the beam quality of Large-Pitch Fibers with mode field diameters well beyond 100 µm...

..8 GW could be achieved by combining active phase shaping with an efficient reduction of the acquired nonlinear phase. Therefore, we used an Ytterbium-doped large-pitch fiber with a mode field diameter of 105 µm as the main amplifier...

..57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub-100 fs, leading to pulse peak powers as high as 3.2 MW...

..In this Letter, we present the experimental realization of thulium-doped very large mode-area fibers based on the large-pitch fibers with record mode-field diameters exceeding 60 μm and delivering more than 52 W of output power...

..This causes a very homogenous energy distribution during the burst. The output burst has a repetition frequency of 20 Hz, is 200 μs long and, therefore, contains 2000 pulses at a pulse repetition rate of 10 MHz...

..Due to its simplicity and maintenance-free operation, the laser scheme holds great potential for bio-medical applications outside laser laboratories...

..The most promising design is evaluated in terms of mode area scaling with a view to mode field diameters above 100 µm. Detailed requirements on the accuracy of the core index matching are deduced...

..This study provides guidelines for the use of spectral filtering elements, such as long period gratings, for Raman scattering inhibition in real-world high power fiber amplifiers...