The generation of sub-10 ps pulses around a wavelength of 2 μm with pulse energy at millijoule-level in a compact CPA-free amplifier chain is presented. This laser source covers a broad range of pulse repetition frequencies from 1 to 100 kHz with a pulse peak power from 136 to 17MW, respectively. We used highly doped Ho:YLF crystals to achieve an overall amplification factor of almost 52 dB. A characterization of these crystals regarding upconversion losses and attainable small-signal gain supports this work.
Amplification of a gain-switched laser diode is demonstrated in an all-fiber based setup. The amplified spontaneous
emission between two consecutive pulses was investigated quantitatively in the time domain. A maximum pulse energy
of 13 μJ at a repetition rate of 1 MHz and a pulse duration of 40 ps was extracted, corresponding to a peak power of 270
KW. Temporal pulse deformation due to intrapulse Raman scattering was observed.
We present experimental results with a 10W-Nd:YVO<sub>4</sub>-laser, which is Q-switched with a single crystal photo-elastic
modulator made of LiTaO<sub>3</sub>. This allows a simple setup driven by voltage amplitudes in the order of 10 V. We observed
stable and unstable pulse sequences. In stable operation a 127 kHz - pulse sequence with 70ns pulse width and 1100 W
peak power was achieved, while the average power remained constant at 10W.
A high-power, single-frequency, ytterbium doped photonic crystal fiber amplifier using a Nd:YAG non-planar ring
oscillator seed source is reported. The system delivers up to 148 W of output power and a slope efficiency of 76% with
respect to the launched pump power. At maximum output power the amplified spontaneous emission was suppressed by
more than 40 dB and a polarization extinction ratio of 28 dB was obtained. Single transverse-mode operation with M<sup>2</sup>
values better than 1.2 was measured by a standard method. To investigate the real overlap of the photonic crystal fiber
transverse-mode with the Gaussian fundamental-mode, sensitive beam quality measurements with a Fabry-Perot ring-cavity
premode cleaner will be presented.
In diode pumped Nd:YAG lasers the quantum defect is the most important parameter determining the thermal load of
the laser crystal. This can be dramatically reduced by pumping directly into the upper laser level. Therefore a high
power end-pumped Nd:YAG laser with direct pumping into the upper laser level will be presented. An 8 bar diode stack
with central wavelength of 885 nm and a spectral width of 2.5 nm was used to pump a diffusion bonded Nd:YAG
crystal with total length of 62 mm and 5 mm in diameter. With an absorbed pump power of 438 W an output power of
250 W was realized. For further power scaling a multi-segmented laser rod was used and up to 276 W of output power
was achieved. Further investigations on thermal load and thermal optical effects will be presented.
For the spaceborne laser-altimeter (BELA) of ESA's BepiColombo mission a master-oscillator-power-amplifier system (MOPA) is presented. The specified system-requirement is a pulsed laser source with a nearly diffraction limited beam (M<sup>2</sup> < 1.6) that combines high pulse energy of about 50 mJ at less than 10 ns pulsewidth and up to 20 Hz pulse repetition rate with the stringent environmental conditions at space missions. A low-mass (< 1.3 kg) and high optical-to-optical efficiency (> 15 %) laser setup is required. Stable operation at a temperature range of at least 25 K for the MOPA system and 15 K for the pump diodes has to be guaranteed. Both oscillator and amplifiers are longitudinally pumped by fiber coupled QCW laser diodes. The performance of a longitudinal pumped system is, because of the longer absorption path, less sensitive to pump wavelength variations due to temperature changes of the laser pump diodes. The pump-pulse duration of 200 μs represents as a trade-off between output energy and efficiency of the whole system. The Nd:YAG oscillator was passively Q-switched with Cr<sup>4+</sup>:YAG crystal as a saturable absorber. With 100 W of peak pump power a nearly diffraction limited (M<sup>2</sup>≈ 1.2) laser pulse with a duration of 2.8 ns and a pulse energy of 2.4 mJ was generated. The output beam of the oscillator was amplified in a two stage amplifier. A maximum of 62 mJ pulse energy was achieved by pumping each crystal with a peak pump power of 600 W.