Polycrystalline CuO samples are irradiated in UHV by excimer laser pulses at 308nm. Mass spectrometry combined with time-of-flight measurements is used to determine the composition of the desorbing particles and the desorption mechanisms. Additional information is provided by Scanning-Electron-Microscopy of the etched surfaces. At fluences below 1.8 J cm−2 the products Cu, O and O2 are desorbed by a purely thermal mechanism at temperatures up to 6000 K and a copper rich surface mask is formed. At higher power densities an additional ablative contribution is monitored which increases with power density, and much less surface area is covered by a Cu-rich mask.