Abstract. Laser nitriding of Armco iron in nitrogen was studied for KrF-excimer-laser irradiation. The influence of the energy density and number of pulses on the nitrogen take-up and the nitride phases formed was investigated using Resonant Nuclear Reaction Analysis (RNRA) and Mssbauer spectroscopy. Besides the original -iron, austenite -Fe(N), martensite -Fe(N), -Fe N, and -Fe N , were identified. The fraction of the -phase was found to increase with the number of pulses and the energy density. A threshold energy density of 1.8(2) J/cm for the laser nitriding process was found.