In the context of lifetime of optics in laser systems in space, spot size dependencies of laser induced damage thresholds have been investigated. The measurements were performed with two different Nd:YAG laser systems at 1064 nm with pulse durations of 8 and 50 ns and repetitition rates of 10Hz and 3kHz, respectively. The effective beam diameter was varied in the range of a few microns up to some tens of millimetres using several focussing optics. In preparation of the experimental analysis, simulations have been performed to determine the difference of the linear evaluation algorithm and a more sophisticated theoretical description of the damage threshold. Correspondence of simulated and experimental results should reveal information concerning the applicability of small spot sizes to standardized damage tests.