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The European Space Agency is developing its first spaceborne LIDAR for global monitoring of wind velocities. ALADIN, to be launched on board ADMAeolus in 2008, is a pulsed Nd:YAG laser with about 120 mJ of pulse energy at 355 nm and a repetition rate of 100 Hz during bursts. Within the projected mission duration of three years, this gives a lifetime requirement of close to 5 billion pulses. While laser-induced damage thresholds of optics in vacuum (possibly contaminated by small amounts of organic compounds) can differ from atmospheric conditions, their damage behaviour is generally poorly understood. The European Space Agency has therefore established a test campaign to measure the power handling of all the instrument optics with several European laboratories participating. In the Optics and Opto-Electronics laboratory at ESTEC, a laser-induced damage threshold (LIDT) test facility has been set up with a 50 Hz Nd:YAG test laser. The pulse energy is 700 mJ at 1064 nm. This allows us to recreate the laser pulse conditions to which the ALADIN optics will be exposed. The flattop beam profile of the test laser irradiates the optics with uniform fluences and relatively large spots (up to 1mm across) at damaging intensities. Damage tests are performed with up to 1 million pulses per test spot according to the S-on-1 test ISO-11254 standard, requiring typically 10 days to test one sample. With such extended tests, we can predict the laser-induced damage threshold over the ALADIN lifetime with improved accuracy.

Laser-induced damage testing of optics for the ALADIN laser