We report on the generation of 830 W compressed average power at 78 MHz pulse repetition frequency and 640 fs pulse
duration. We discuss further power scaling including the issue of transversal spatial hole burning. Therefore, we
describe a low-nonlinearity fiber design capable of producing fundamental mode radiation at ultra high average powers
from short length (range of 1m) and large mode field diameter (>50μm) fibers. In conventional large mode area fiber
most of the core is typically uniformly doped. As a consequence gain factors for the fundamental mode and the next
higher order modes are comparable. Furthermore, the fundamental mode extracts inversion only in the central part of the
core according to its intensity profile, leading at high pump and signal power levels to high and unused inversion density
with a strong overlap with higher order transversal modes. In experiments this leads to a threshold-like onset of mode
instability, originating from mode competition. Finally, this effect avoids further power scaling. The presented fiber
features an optimized doping profile to prefer the amplification of the fundamental mode. In addition non-extracted
inversion is minimized avoiding the issue of transversal spatial hole burning. As a consequence ultrafast fiber laser
systems with novel performance are in reach, i.e. systems delivering simultaneously >1GW peak power and >1kW
average power. In a first iteration a ROD-type fiber with 60μm MFD and 1.7m length was used in a CPA system to
produce pump power limited 355 W of average power at 1 MHz.
In this contribution we introduce a simple scheme to spectrally combine four single beams using three low-cost
dielectric interference filters as combining elements. 25 ns pulses from four independent and actively Q-switched fiber
seed-sources are amplified in a single stage fiber-amplifier. Temporally and spatially combined 208 W of average
power and 6.3 mJ of pulse energy are obtained out of a fiber-based laser system. A detailed observation of beam quality
as well as the thermal behavior of the combining elements have been carried out and reveal mutual dependency. The
deterioration of beam quality can be led back to thermal induced wave-front distortions on the part of the interference
filters. This effect as well as other influences on M2 will be discussed and compared to the competing combining
approach with dielectric gratings.
In this contribution, we report on spectral combination of four sub-5ns pulsed fiber amplifier systems with an average
output power of 200W at 200kHz repetition rate resulting in 1mJ of pulse energy. A dielectric reflection grating is used
to combine four individual beams to one output possessing a measured M2 value of 1.3 and 1.8, respectively,
independent of power level. Extraction of higher pulse energies and peak powers will be discussed.
We report on the generation of microjoule level picosecond pulses from a mode-locked Yb-doped LMA fiber laser
operating in the purely normal dispersion regime. The self-starting oscillator stabilized with slow relaxation
semiconductor saturable absorber (SAM) emits 11 W of average power at a pulse repetition rate of 10 MHz,
corresponding to a pulse energy of 1.1 μJ. The laser produces a 0.4 nm narrow emission line with 310 ps output pulses.
In the femtosecond operation, the oscillator stabilized with fast relaxation SAM emits 9 W of average power at a pulse
repetition rate of 9.7 MHz, corresponding to a pulse energy of 927 nJ. The laser produces positively chirped output
pulses of 8 ps which are compressed down to 711 fs, corresponding to megawatt peak power. To our knowledge this is
the first time that mode-locked fiber oscillators can generate higher pulse energies of beyond microjoule-level at high
average output power.
We show spectral combination of pulsed fiber laser systems for the first time to our knowledge. In this proof of principle
experiment, two directly modulated wavelength-stabilized tunable external cavity diode lasers (ECDL) serve as
independent seed sources. Each signal is amplified in a two stage ytterbium-doped fiber amplifier. The spatial overlap is
created using a transmission grating with a combining efficiency as high as 92 %. No beam quality degradation has been
observed for the combined beam compared to a single emission. An electronic delay is used to adjust the temporal
overlap of the pulses from the spatially separated amplifier setups. The presented approach offers an enormous scaling
potential of pulsed fiber laser systems, which are generally limited by nonlinear effects or fiber damage. We show that
the huge gain bandwidth of Yb-doped fiber amplifiers and the high diffraction efficiency of dielectric reflection gratings
in this wavelength range yield potential for a combination of up to 50 channels. For state-of-the-art ns-amplifier systems
> 100 MW of peak power, > 100 mJ of pulse energy and average powers of > 10 kW seem feasible.
We report on the generation of 265 nJ ultra-short pulses from a mode-locked Ytterbium-doped short-length large-mode-area
fiber laser operating in the dispersion compensation free regime. The self-starting oscillator emits 2.7 W of average
power at a pulse repetition rate of 10.18 MHz. The pulses have been compressed down to 400 fs, corresponding to 500
kW peak power. Numerical simulations confirm the stable solution and reveal the mechanisms for self-consistent intra-cavity
pulse evolution. The pulse energy is one order of magnitude higher than so far reported for fiber oscillators in the
1 μm wavelength region. To our knowledge this is the first time that mode-locked fiber oscillators can compete in terms
of pulse energy and peak power with most advanced bulk solid-state femtosecond lasers.
We report on an optical parametric amplification system which is pumped and seeded by fiber generated laser radiation.
Due to its low broadening threshold, high spatial beam quality and high stability, the fiber based broad bandwidth signal
generation is a promising alternative to white light generation in bulky glass or sapphire plates. As pump source we
propose the use of a high repetition rate ytterbium-doped fiber chirped pulse amplification system.
We report on an Yb-doped photonic crystal fiber based CPA system delivering 90.4
W average power of 500 fs pulses at a repetition rate of 0.9 MHz corresponding to a pulse
energy of 100 &mgr;J.
Photonic crystal fibers consisting of a solid fused silica core surrounded by a regular array of sub-micron air-holes have been shown to operate with single mode core well above 30 μm in active laser geometries as well as passive beam delivery fibers. Novel designs based on the combination of stress applying elements that are index matched to the holey cladding have recently been emerged. In this report we summarize the properties of these polarization maintaining photonic crystal fibers. Beside the characterization of the polarizing window and birefringence, high power laser and amplifier configurations using these fibers are demonstrated and first experiments concerning the temperature sensitivity of the polarizing properties are presented.
The generation of high energy femtosecond pulses in Optical Parametric Amplifier (OPA) pumped by fiber laser at a repetition rate of 1MHz is reported. Highly nonlinear fibers are used to create an intrinsically synchronized signal for the parametric amplifier. Seeding the OPA by a supercontinuum generated in a photonic crystal fiber, large tunability extending from 700 nm to 1500 nm of femtosecond pulses is demonstrated, with pulse energies as high as 1.2 μJ. Generating the seed using only SPM in a standard fiber, broadband amplification over more than 85 nm and subsequent compression down to 46 fs in a prism sequence are achieved. Pulse peak powers pulses above 10 MW together with 0.5 W of average power is achieved. This system appears to be very interesting due to scalability of pulse energy and average power of both involved concepts: fiber laser and parametric amplifier.
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