Untersuchung von Laserstrahlquellen mit Erbium-dotiertem YLuAG für Lidar-Systeme zur $CH_{4}$-Detektion

Aachen (2019, 2020) [Dissertation / PhD Thesis]

Page(s): 1 Online-Ressource (112 Seiten) : Illustrationen, Diagramme

Abstract

Merlin (Methane Remote Sensing Lidar Mission) will be the first active satellite-borne Lidar-instrument for measuring the greenhouse gas CH4 and is planned to be launched in 2024. It will contain a laser beam source for producing narrow-linewidth (single-frequency) laser pulses with a wavelength of 1645,552 nm (in vacuum). This beam source will be based on non-linear frequency conversion of laser pulses at 1064 nm. An alternative for producing appropriate laser pulses is its direct generation with an Erbium-doped laser crystal. This approach promises to be more robust, less complex and more efficient. In order to generate precisely the required wavelength an Yttrium-Aluminum-Garnet/Lutetium-Aluminum-Garnet mixed crystal is used. This crystal was developed and grown at the University of Hamburg prior to this work. In this work, investigations into Erbium-doped Yttrium-Lutetium-Aluminum-Garnet (Er:YLuAG) as a laser crystal for pulsed laser beam sources are reported for the first time. In end-pumped q-switched rod oscillators, a pulse energy of up to 6 mJ at a repetition rate of 100 Hz, a pulse duration of 80 ns and an optical efficiency of 2,2 % are measured. These pulses are amplified to 9,8 mJ at an efficiency of 0,2 % in an Innoslab-Amplifier. Appropriate spectral properties of laser pulses in single-frequency operation are demonstrated by measuring the methane absorption line with its sub-structure at 1645,552 nm in a gas cell. A simulation model is validated with the experimental data and used to identify potential for further scaling of efficiency and pulse energy of the laser beam source. It is found that the laser-induced damage threshold (LIDT) is the main technical property that limits the achievable efficiency. LIDT of a coated Er:YLuAG crystal is measured to be in the range of 35-40 J/cm². Finally, radiation resistance of Er:YLuAG with proton and gamma radiation is tested and hence demonstrated, that Er:YLuAG is sufficiently radiation resistant and that codoping the crystal with Cerium further increases the radiation resistance. In total, with the work described herein the feasibility of an Er:YLuAG-based laser beam source for a Merlin-type mission scenario is demonstrated. Technical challenges are identified and possible mitigation strategies are proposed.

Authors

Authors

Meissner, Ansgar

Advisors

Poprawe, Reinhart
Huber, Günter

Identifier

  • REPORT NUMBER: RWTH-2020-05373

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