Ytterbium-doped Large Pitch Fibers with very large mode areas are investigated in a high power fiber amplifier
configuration. An average output power of 294 W is demonstrated, while maintaining robust single-mode operation with
a mode field diameter of 62 μm. Compared to previous active large mode area designs the threshold of mode instabilities
is increased by a factor of about 3.
We report on nonlinear optical compression of passively Q-switched pulses accessing sub-10 ps domain, which is so far
dominated by mode-locked systems. The concept implements the SPM-induced spectral-broadening of passively Q-switched
microchip pulses in optical waveguides and a supplementary compression with bulk optics e.g. a pair of
diffraction gratings or a chirped-Bragg-grating. Used seed-source is a fiber-amplified, passively Q-switched microchip
laser operating on a single longitudinal mode and consists of a monolithically bonded combination of Nd:YVO<sub>4</sub>-crystal
and semiconductor saturable absorber mirror. The microchip laser provides pulses with durations of 100-150 ps, pulse
energies of ~200 nJ at various repetition rates from hundreds of kilohertz to more than a megahertz, and line width of
~20 pm at wavelength of 1064nm. During the amplification process in the photonics crystal fiber, the pulses are
spectrally broadened to up to ~0.7nm at energy of 17μJ. Using a diffraction grating compressor with 1740 l/mm, the
pulses are compressed to duration as short as 6ps assuming a numerically calculated de-convolution factor of 0.735. To
the best of our knowledge, this is the first reported realization of nonlinear compression of the Q-switched pulses and the
shortest pulses from a passively Q-switched laser system.
We report on a diode-pumped, monolithic and passively Q-switched microchip laser generating 200 ps pulses at a
wavelength of 1064 nm with a repetition rate of up to 2 MHz. By varying the pump intensity we can change the
repetition rate in the range from 100 kHz to 2 MHz and achieve pulse energies from 400 nJ to 130 nJ respectively, while
still maintaining singe transversal and longitudinal mode operation. The microchip laser is based on Nd:YVO<sub>4</sub> as the
gain medium and a SESAM as the passive Q-switch. It is monolithically bonded with spin-on-glass as the bonding
agent. The timing jitter was measured to be shorter than 40 ns for low and 2.5 ns for high repetition rates resulting in a
relative timing jitter smaller than 1%. The output of this type of laser can be amplified easily to the range of few tens of
watts using only one amplification stage based on a photonic crystal fiber. The combination of picoseconds pulses, high
average power and high repetition rates makes this system very interesting for many applications like e.g.
micromachining with high processing speed and nonlinear frequency conversion with high average power.
We report on a hybrid fiber MOPA + solid-state amplifier for frequency conversion and compare a hybrid
scheme versus all- fiber MOPA. Using a thoroughly designed master oscillator and optimized fiber amplifiers we were
able to achieve 15-30ns long pulses at average powers above 20 W with a good spectral quality and suppressed SBS.
Bulk Vanadate amplifiers boosted the 1064nm output power to greater 65W at pulse repetition rates of 300-500 kHz.
More than 35 W in green and 20 W of UV light has been obtained at pulse repetition rates above 300 kHz and pulse
energies of 30-100 μJ.