[en] Subsurface damage in silicon formed by ion implantation and the residual damage after annealing have been successfully evaluated by measuring the photo-acoustic displacement (PAD) induced by an intensity modulated pump beam. The PAD was detected by a laser interferometric probe with a sensitivity of 0.1 picometers in a noncontact manner. A temperature rise within the subsurface damage due to a decrease in the thermal conductivity leads to significant thermal expansion and causes a displacement on the sample surface. Therefore, subsurface damage can be monitored by measuring the PAD. Experimental results for As⁺ and B⁺ implanted samples indicate that recrystallization of ion implant damage by annealing can be monitored by this technique. Samples of higher doses (> 10¹⁴/cm²) have residual damage even after annealing at 800 C for 30 minutes. The results for high-energy (2MeV) implanted samples also show that the secondary defects after annealing, which are formed in a deep region a few microns under the surface, can be detected with high sensitivity