Testing of laser optical components for spaced-based laser systems

Abstract

In this paper we address the qualification of optical components used in space based laser systems with special emphasis on nonlinear optical crystals, performed at the DLR optics qualification laboratory. The motivation for this activity is due to upcoming ESA space laser missions like ADM-Aeolus, EarthCARE, or BEPI Colombo. The ADM-Aeolus satellite is operating a Doppler wind LIDAR laser source named ALADIN (Atmospheric Laser Doppler Instrument), and will be the first system to be launched, scheduled in 2011. ALADIN aims at measuring wind profiles on a global scale as required by the climatology and meteorology fraternities. In all these missions, high performance laser systems rely on the efficient and long term stable operation of passive and active optical components. Active optical components like nonlinear crystals are more vulnerable to degradation than conventional passive optics due to the necessity of operating them at high fluence values to increase the efficiency, their susceptibility to various deleterious effects (e.g. gray tracking) and available crystal and surface quality. Nonlinear optical crystals under inspection which are suitable for SHG and THG conversion are LBO, BBO, KTP and BiBO. As the optics will be exposed to relatively high fluence levels (up to 20 J/cm2) at various wavelengths (1064 nm, 532 nm, 355 nm) of nanosecond pulses (typically 3,5 ns FWHM) and are required to have a lifetime of several years equating to several billions of laser shots emitted overall, there are stringent requirement necessitating extensive test campaigns to identify critical laser optics for risk mitigation purposes. In addition to the laser-damage tests, frequency conversion crystals are exposed to high energy radiation at doses which are typical in the space environment to identify