Techniques are disclosed for an improved boresighting apparatus and related method for boresighting a light source to an imaging sensor, and for an improved material to be used in a target object in such a boresighting apparatus. For example, an apparatus for use in boresighting may include a catadioptric element and a target object, where the catadioptric element is configured to focus a laser beam from the light source and also to collimate light emitted from the target object at a different wavelength than the laser beam to be detected by the imaging sensor for indicating the location of the focused laser beam. The target object may, for example, comprises a fluorescent optical material doped with one or more optically active ions to absorb light having the wavelength of the laser beam and emit light in one or more wavebands detectable by the imaging sensors.