Abstract: The surface wettability and mechanical properties of Nd: YAG crystals were investigated to study the influence of plasma jet on Nd: YAG crystals by using self-developed plasma equipment at room temperature． The results show that the plasma has significant effects on surface properties of Nd: YAG crystals，and the wettability of Nd: YAG crystals with three different roughness is improved after plasma modification． Especially，the smooth surface changes from hydrophobic to super-hydrophilic，and the good state of hydrophilicity lasts 30 hours． The improvement of wettability of Nd: YAG surface mainly lies in the increase of oxygen-containing functional groups on the surface of the modified Nd: YAG crystals． The microhardness remains unchanged within 0 to 11h，decreases first and then increases within 11 to 22h，and remains stable within 22 to 35h after the modification． Especially，a minimal microhardness occurs between 11 to 22 h after the modification． Under the peak load of 15. 0，30. 0 and 70. 0mN，the average microhardness decreases by 56. 2%， 45. 0% and 31. 6%，respectively． And the morphology of some indentations shows features of“ladder”and“shadow” due to the rapid increase of plasticity on Nd: YAG surface 11 hours after the modification．

Key words: plasma, modification, Nd, YAG crystal, wettability, nanoindentation, microhardness