A dual mode mirror imaging system is described having a Cassegrain-type
objective assembly having a primary mirror with a hole in its center and
a secondary mirror spaced in front of the primary mirror, and imager
optics disposed in the hole. The secondary mirror is adapted to receive
laser wavelength light and infrared wavelength light reflected from the
primary mirror and to reflect the light back through the imager optics to
focal plane. The secondary mirror has one reflecting surface for the
laser light and another reflecting surface for the infrared light. The
pair of reflecting surface is positioned to change the optical path
length between the laser light and the infrared light so that the laser
light and the infrared light are imaged at the same focal plane without
defocusing.