Nanoparticles (NPs) were produced by ablating tungsten and boron-carbide (B4C) target materials in atmospheric pressure nitrogen ambient using ArF excimer laser pulses. The size distributions of the NPs formed during the ablation were monitored-within a 7-133 nm size window-by a condensation particle counter connected to a differential mobility analyzer. The laser repetition rate was varied between 1-50 Hz, and the fluence was systematically changed in the range of 0.5-15 J/cm(2), for both materials, allowing a comparative study in an extended laser parameter regime. The multishot ablation threshold (Phi(th)) of B4C Was determined to be similar to 1.9 J/cm(2) for the laser used (ArF excimer, lambda = 193 nm). Similarly to earlier studies, it was shown that the size distributions consist of mainly small nanoparticles (< similar to 20 nm) attributed to a non-thermal ablation mechanism below Phi(th). An additional broad peak appears (between 20 and 40 nm) above Phi(th) as a consequence of the thermally induced macroscopic ablation. Chemical composition of deposited polydisperse nanoparticles was studied by X-ray photoelectron spectroscopy showing nitrogen incorporation into the boron-carbide. (c) 2005 Elsevier B.V. All rights reserved.