An experimental technique has been developed to directly measure flow velocity and Mach number in a supersonic hydrogen fluoride laser. The technique uses a tunable diode laser source to probe the laser cavity at an angle to the flow creating a Doppler shifted lineshape. The amount of Doppler shift can be related to the flow velocity. The diode laser was traversed in the vertical direction to produce velocity and Mach number profiles. (C) 2003 Elsevier Science B.V. All rights reserved.