Vacuum laser damage test bench

Abstract

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).

Laser-induced damage testing of optics for the ALADIN laser

“…Space qualification of the laser requires that every batch of unique component is tested with respect to their laserinduced damage threshold in vacuum. This is particularly significant since experiment shows that the damage threshold of coatings in vacuum can be lower than in air [2] and may hence deviate from manufacturer specifications. A second risk is optical fatigue in the course of the mission.…”

“…We have plotted the function specified by the ISO standard [6] (1) where H thr (N) is the threshold for N shots, H thr,1 and H thr, are the damage threshold for one shot and an infinite number of shots, respectively, and specifies the rate of aging. For the purpose of comparison, we have also included the function proposed by Allenspacher et al from DLR in [2]. At 5 billion pulses, the ISO-standard extrapolation gives an estimate of 3.7±0.7J/cm 2 , while the DLR function extrapolates to 5.2±1.0J/cm 2 , demonstrating the importance of the model used and the difficulty in performing an extrapolation.…”

“…For the purpose of comparison, we have also included the function proposed by Allenspacher et al from DLR in [2]. At 5 billion pulses, the ISO-standard extrapolation gives an estimate of 3.7±0.7J/cm 2 , while the DLR function extrapolates to 5.2±1.0J/cm 2 , demonstrating the importance of the model used and the difficulty in performing an extrapolation. …”

“…In a very limited period of a few months DLR tested all the unique optics of the ALADIN laser. The tests themselves have all been described in [2], and will not be described in more detail here.…”

Degradation mechanism of laser-induced damage of porous ZrO2/SiO2 high reflective films in vacuum

“…However, the reason why the laser-induced damage threshold (LIDT) of high reflective films is decreased in vacuum [5][6][7] has not yet been well understood and further studies are required to elucidate the factors that influence this damage threshold. These factors influencing laser-induced damage in vacuum were complicated, and many studies put more focus on the external causes such as organic contaminations outgassing from materials present in vacuum environment.…”