A diagnostic method for high power CO2laser beams is presented. The technique features imaging of high intensity infrared radiation via the thermally induced luminosity of high velocity charcoal particles contained within an air stream. The method is particularly convenient for determination of focal position, depth of field, beam diameter, and spot size. Variations of these parameters with power level are easily observed utilizing this charcoal powder imaging method. Using this ‘‘real‐time’’ technique, focal spot size and location accuracy are ±0.1 and ±1 mm, respectively. Results are shown to be independent of micro‐particle size within specified limits. As a result, periodic, fine laser‐workpiece adjustment is now cost effective when working with high power lasers. ©1994 American Institute of Physics.