through the optical element 16 in the front housing opening 15 forming an optical path for projection of a laser beam 21 from the laser transmission unit 20 the central longitudinal axis of the laser transmission unit 20 extending through the housing forward end opening 15 is defined as the laser beam optical axis 31 in the preferred embodiment a cw laser transmission unit is used having a basic frequency band width in the infrared or visible light range in alternate embodiments a pulsed laser transmission unit may be used a beam splitter 30 is positioned between the laser transmission unit 20 and the housing forward end opening 15 in the optical axis path 31 the beam splitter can be an optic with a hole or a short flat surface the beam splitter 30 in this embodiment of the invention is comprised of a mirror 32 positioned at a 45 degree angle to the optical path 31 however the mirror 32 may be positioned at any other desired angle the mirror 32 has an inner surface 33 and an outer surface 34 the inner surface 33 is defined as that surface generally facing the laser transmission unit 20 the outer surface 34 is defined as that surface generally facing the housing forward end opening 15 the mirror 32 is designed to reflect a certain amount of the energy incident on it and to be transparent to the remaining the.