An aluminum‐coated tapered fiber probe, as used in near‐field scanning optical microscopy (NSOM), is heated by the light coupled into it. This can destroy the probe or may modify the sample, which can be problematic or used as a tool. To study these thermal effects, we couple modulated visible light of various power through probes. Simultaneously coupled infrared light senses the thermal effects. We report their magnitude, their spatial and temporal scales, and real‐time probe damage observations. A model describes the experimental data, the mechanisms for induced IR variation, and their relative importance. © 1995 American Institute of Physics.