This work summarizes the results from an extensive test campaign in which space-based laser optics were qualified for the upcoming ESA ADM-Aeolus mission. 14 different types of optical components from different suppliers were tested at the Nd:YAG laser wavelength according to the ISO standard 11 254 -2 for multiple pulse testing. A new technique based on transient pressure sensing was developed to monitor the occurrence of damage on a sample surface exposed to a vacuum environment. Parallel testing of reference samples showed a distinct degradation under vacuum compared to atmospheric or pressurized environment. For all samples tested we found a typical behavior in the characteristic damage curves attained: A sharp drop in LIDT for small pulse numbers followed by a smooth decrease for larger pulse numbers (laser fatigue effect).
Abstract-During the Aeolus laser and instrument transmitter development it was shown that atmosphere quality was one major limiting factor for high energy UV laser operation at ambient pressure. As already proven in literature operation can only be safely obtained in the presence of oxygen ([1] to [6]).Furthermore, air quality has to be adequately controlled and monitored to ensure that no catastrophic event occurs. On-line qualitative (no/no-go discriminator) can be obtained using fluorescence monitoring of the laser beam, while GC-MS remains the technique of choice to quantitatively evaluate suitability of air supply a priori. LIC testing is in the process of being adapted to trace contaminant evaluation.Finally, the formation of laser generated absorbing features is described, during air irradiation. The potential root causes of these absorbing dot-like features are explored, using optical measurements, microscopic inspections and chemical analysis. Current results indicate organic deposits associated with metallic particles and a presence of phosphates.Index Terms-High Energy UV Laser, LIC/LIDT, GC-MS, trace gas analysis, absorbing features.
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