We average over the temperature while the ball is in contact and out of contact with the surface. For the second measurement, we synchronize the gating of the Ar laser with the arrival of the ball bearing in the contact region. By incrementally increasing the delay between initial contact and the Ar pulse, we can sweep out the temperature rise as a function of position within the contact region. We average over several contacts at each delay to improve the signal to noise ratio. Shown below are some results from sliding experiments at high velocities and low loads.
Temperature measurements are accurate to within about two degrees.