The present invention provides for a novel method and apparatus for the simultaneous generation and detection of optical diffraction interference pattern on a photo detector. The monitoring method and apparatus disclosed herein comprises of a (any) continuous wave coherent collimated beam of light (or a laser) falling on an (any) optically reflective coating on the surface of the body with inherent vibrations, or with manifest vibrations induced from another source through any medium where the said light is reflected, and then received on the surface of a (any) photo detector in such a way that the received light falls partially on the active sensing area, and partially on the outer perimeter of the active sensing area.