Temporal variations of substrate surface temperature in scanning Ar thermal plasma jet has been investigated based on an analysis of transient changes in optical reflectivity. The accuracy of the temperature measurement has been evaluated to be 30 K at temperature around 1760 K. The maximum surface temperature (T-max) is controlled in the range from similar to 960 to similar to 1780 K with keeping the annealing duration (t(a)) around similar to 3 ms by changing the Ar gas flow rate 0 and distance between the plasma jet and the substrate (a) under a constant scanning speed (v) of 500 mm/s. (c) 2006 Elsevier B.V. All rights reserved.