used and are readily available to supply power for the requirements of the invention simple low powered lasers are well known in the art which generate a visible laser beam small dc powered laser diodes are well known and commercially available the function of the horizontal scan mirror is to rapidly and repeatedly direct the laser beam along a horizontal path the u201c y u201d axis this is accomplished by providing a rotating horizontal scan mirror which comprises a plurality of vertical reflecting surfaces 20 in a horizontal cross section the horizontal scan mirror is a symmetrical regular polygon as shown in fig1 in the one embodiment illustrated the polygon has 16 sides and therefore has 16 reflecting surfaces 20 as the mirror 12 is rotated about the u201c z u201d axis and the laser beam is reflected from one end of a reflecting surface to the other the angle of incidence u03b8 between the laser beam at the reflecting surface changes as a result the laser beam oscillates along the u201c x y u201d plane the frequency of oscillation is determined by the speed of rotation of the horizontal scan mirror and the number of reflecting surfaces around the circumference of the mirror for example if the horizontal scan mirror shown in fig1 is rotated at 2 revolutions per second the laser beam will oscillate 32 times per second or at 32 hz the vertical scan mirror is configured and positioned to receive the laser beam reflected off the horizontal scan mirror in one embodiment the vertical scan mirror is an elongated mirror assembly having a.