Abstract: The apparatus permits an external target to be viewed along a sight-line by a sensing device and for the projection of a beam of laser radiation (12) towards the target. The apparatus includes a viewing window (10) transparent to radiation at a wavelength to which the sensing device is sensitive and inclined at an angle to the sight-line. The window (10) has a viewing area through which the target may be viewed and a laser output area through which the laser beam passes. An anti-reflection coating is formed on that surface of the viewing window (10) remote from the target. Optical deflector means (16) are provided for deflecting laser radiation reflected from the other surface of the viewing window in the laser output area into the viewing area of the window for reflection into the field of view of the sensing device.