An optical velocimeter probe a device to illuminate a volume of measurement in which there may pass particles, and an optical detector to produce an electrical signal x(t) in response to the passage of a particle in the illuminated volume. It also includes a device to extract information representing the velocity v of particles from the electrical signal, including, in particular, a device to convert the electrical signal x(t) into a complex signal .sub.x (t), an apparatus to set up a self-correlation function r.sub.x (m) of the signal x(t), and a device to estimate the velocity v from the computation of the phase .phi..sub.x (m) of the function r.sub.x (m).