A Doppler broadened two-level medium, saturated by a strong beam with
finite diameter, and probed by a wide weak beam gives rise to non-lore
ntzian lineshapes whose derivatives linewidths are almost free from sa
turation effects. Experiments with a CO2 laser on SF6 verified such li
nes which can be useful for measuring collisional relaxation rates fre
e from saturation broadening.