As part of the European Space Agency's AEOLUS mission, the global wind distribution in the atmosphere is currently being measured with a satellite based Doppler lidar. For the AEOLUS-2 mission, a more powerful laser is required which can emit single frequency pulses of 150 mJ energy at a pulse repetition rate of 50 Hz and a wavelength of 355 nm. Fraunhofer ILT is currently developing an engineering model of the laser beam source in cooperation with Airbus Defense and Space Germany. The work on the laser housing and heat removal system is performed by Airbus whereas the work on the laser opto-mechanical assembly is performed by ILT. This work is based on the results of previous projects and focuses on maximizing the use of heritage: The required optical parameters in the infrared have been validated by means of a breadboard demonstrator within the NIRLI project and the optomechanical platform suitable for AEOLUS-2 has been developed in the frame of the OPTOMECH, FULAS and MERLIN projects. For the engineering model presented in this article the proven optical design supplemented by a frequency tripling unit is transferred to the proven and to a large extent space qualified optomechanical platform with an adapted heat removal system. The design is ready, pending the detailed review.
Airbus Defense and Space GmbH, in cooperation with Fraunhofer ILT, is currently developing an engineering model (EM) of the laser transmitter for the AEOLUS-2 mission in frame of the ESA contract ALTA. . For this follow-up mission, a more powerful Laser transmitter is required, to provide single frequency laser pulses of 150 mJ energy. The design focuses on maximizing the use of the heritage from previous space-borne laser designs of the projects FULAS (ESA, EM-like Technology Demonstrator) and MERLIN (DLR/CNES, French-German Climate Mission). The FULAS laser comprises INNOSLAB based MOPA delivering IR laser pulses in the 100 mJ class at 100 Hz PRF. It has undergone a test program demonstrating outstanding thermal insensitivity and robustness and optical and mechanical stability, showing no degradation or misalignment at all after seven years. The laser transmitter of MERLIN, evolved from FULAS, comprises a scaled MOPA, combined with a subsequent Optical Parametric Oscillator (OPO) for frequency conversion. While the Laser opto-mechanical assembly (LASO) is developed by Fraunhofer ILT, Airbus Defence and Space GmbH is in charge of the system concept and the hermetically sealed Laser Housing (LASH) as well as the innovative thermal control system. This publication will provide insight in the transfer of the FULAS and MERLIN system concepts to the Doppler Wind LIDAR Transmitter. Emphasis will be on the robust thermo-mechanical design, with its thermally and mechanically decoupled optical bench and the sophisticated thermal control system based on heat pipes for effective heat removal directly from the individual heat sources of the system. This design is chosen to provide hands off operation of the Transmitter over life time.
The Franco-German »MERLIN Project« was initiated in 2010. The small satellite MERLIN (Methane Remote Sensing LiDAR Mission) will map the methane in the earth’s atmosphere. Fraunhofer ILT has developed the LiDAR laser source and is currently integrating the Engineering Qualification Model. The laser consists of a laser oscillator pumped by fiber coupled diode laser modules, an INNOSLAB amplifier and KTP-based frequency converter. The amplifier pump is based on qcw stacks which are homogenized in the slow axis direction and focused in the fast axis direction. We will present the design of the pump optics and results of reliability tests. In addition, we will give an outlook on the development of a laser source for a future wind LiDAR mission.
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