Reliable high energy laser sources had been proven in the past to be the bottle neck for space-borne LIDAR instruments. The presented FULAS laser optical design concept and the developed technologies define a technology baseline for a high variety of potential LIDAR applications. The technology provides a reliable space compatible system design, optimized with respect to lifetime and in especial laser induced contamination. The applied design principles and modularity allow proven energy scalability, flexible modes of operation and a manifold of opportunities for tailoring of the output wavelength. The concept, some details of the design and the potential for future application are addressed in this publication

For the spaceborne laser-altimeter (BELA) of ESA´s Bepi Colombo mission a master-oscillator-power-amplifier system (MOPA) is presented. The system-requirement is a pulsed laser source with a nearly diffraction limited beam (M² < 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 variation 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 due to the longer absorption path less sensitive to pump wavelength variations resulting from temperature changes of the laser pump diodes. The pump-pulse duration of 200 µs represents a trade-off between output energy and efficiency of the whole system. The Nd:YAG oscillator was passively Q-switched with a Cr 4+ :YAG crystal as a saturable absorber. With 100 W of peak pump power a nearly diffraction limited (M² ≈ 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.

We report on a compact Nd:YAG amplifier emitting a maximum pulse energy of 14 mJ. By amplifying a passively Q-switched oscillator (M(2)<1.2) a good beam quality of M(2) approximately 1.7 was achieved. The amplifier is diode pumped by an 8 bar diode stack of 800 W power and a nonimaging optic. This optic homogenizes the pump light and transfers it into a 5 mm diameter core doped rod with a centrally neodymium doped region of 3 mm and a samarium doped YAG cladding. We show that this cladding reduces parasitic effects in the laser rod compared to an undoped YAG cladding. Finally, we compare the compact amplifier with an amplifier, which is mode selectively pumped by a fiber coupled pump diode.

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