A fast‐beam deflection technique is used to investigate the transient behavior of a laser‐induced surface plasma generated by CO2‐laser pulses of 2‐kW average power near an aluminum surface in various protective gas atmospheres, with a typical pulse energy of 3.3×10−2J, a pulse repetition rate of 60 kHz, and an average peak power per pulse of 30 kW, corresponding to an intensiy of 6×1012W/m2. As a laterally probing beam, a cw 10‐W CO2laser is used, whose beam is focused into a small volume in front of the surface. The electrons of the laser‐induced plasma passing this volume diffract the cw CO2laser beam, and the resulting beam deflection is determined by means of a partially absorbing CaF2wedge in connection with a fast infrared detector. The evaluation of beam deflection 0.15 cm above the surface renders a maximum electro density of 2×1023m−3for a surrounding argon atmosphere and 0.7×1023m−3for pure helium. Additives of O2reduce the attainable electron density even more. No plasma can be detected below a threshold of, say, 10 mJ energy per laser pulse. It is verified that high electron density as in the case of argon shields the surface against the incoming CO2laser pulses so that material processing, such as welding, is rather poor. Better welding results are achieved in helium‐oxygen mixtures.