The surface of a doped semiconductor wafer is heated locally by means of a pump beam whose intensity is modulated at a first frequency. The heated area is sampled by a probe beam whose intensity is modulated at a second frequency. After the probe beam has been modulated (reflected or transmitted) at the first frequency by the wafer, the modulated probe beam is detected at a frequency equal to the difference between the harmonics of the first and second frequencies to determine dose of the dopants in the wafer. Such or similar type of instrument for measuring dose may be combined with an ellipsometer, reflectometer or polarimeter for measuring dose as well as thickness(es) and/or indices of refraction in a combined instrument for measuring the same sample.