We report a direct observation of the temperature field on a steel specimen during ablation by multiple fermtosecond laser pulses using an infrared thermography technique. From the experimental results and simulation study of the temperature field, we quantified the deposited thermal power into the specimen during the ablation process. We found that more than two thirds of the incident laser power was deposited in the steel specimen when ablated by multiple fermtosecond laser pulses. This result provides further understanding of the heating effect in materials processing by ultrashort laser pulses. (c) 2007 Elsevier B.V. All rights reserved.