Time‐dependent number densities of excited atoms in a discharge‐pumped ArF excimer laser were measured through laser absorption probing with a cw dye laser. The He*(2p 3P) and Ne*(3s 3P2) atoms in the discharge using He/Ar/F2and Ne/Ar/F2gas mixtures were studied. The peak of Ne* and He* atom densities were 1.7×1012cm−3and 2.1×1012cm−3, respectively. The number densities of He*, the laser output power, and the discharge voltage were also measured with varying He/Ne mixture ratio in He/Ne/Ar/F2gas mixtures. Effects of He and Ne buffer gases on the excitation mechanisms of atoms are discussed on the basis of those measured results, and compared with the case of XeCl excimer lasers. ©1995 American Institute of Physics.