摘要 |
A method, of detecting the velocity of a moving object (OBJ) comprising the steps of : passing a beam of coherent light through an optical mask (MA) having a pattern of alternating opaque and non-opaque regions formed thereon, whereby an image of alternating light and dark fringes is projected along the light beam,- causing the moving object to pass through the projected image such that a portion of the light beam is reflected from the moving object as a series of pulses; detecting the reflected light pulses and the frequency of the pulses,- and calculating the velocity of the object as a function of the pulse frequency and the known separation of the fringes of the image. |