Shared aperture dichroic active tracker with background subtraction

#1. Technical Field

#The present invention relates generally to systems for tracking moving objects in conjunction with a laser beam and, in particular, to a self-referencing, imaging tracker that separately images target and target laser hit spot radiation to directly reference the laser hit spot relative to the target in a common coordinate system, thereby allowing the laser weapon to be locked onto, and maintained at, a desired target aim point until a target kill is achieved.

#2. Discussion

#FIG. 1A is a block diagram illustrating the tracker according to a preferred embodiment of the present invention;

#FIG. 1B is a block diagram illustrating the tracker according to a second preferred embodiment of the present invention;

#FIG. 2A illustrates the components of the optical subsystem of the first preferred embodiment shown in FIG. 1A in more detail;

#Referring to FIG. 1A, a missile tracker according to a first preferred embodiment of the present invention is shown generally at 10. The tracker is implemented in conjunction with a laser weapon 12 to steer a laser beam 14, produced by the laser weapon, into engagement with a target, such as the missile shown at 16. The tracker functions first to lock the target in its field-of-view, then to drive the difference between the desired target aim point, indicated by the cross hairs at 18, and an actual laser beam target engagement point, referred to as the laser beam hit spot 20, to zero, thereby increasing the probability of a target kill.

#As will now be described, the tracker of the present invention images both the missile 16 and the laser beam hit spot 20 in a manner that minimizes loss of missile information using one of two possible implementations which will be referenced throughout as variant 1 and variant 2. FIGS. 6 and 7 illustrate an alternative embodiment of the invention which utilizes a shared aperture for the outgoing mid IR range radiation of the laser beam 14 and the near IR range indication reflected from the target 16.

#In variant 1, as shown in FIG. 1A, the system includes an illuminator laser 22 that preferably operates in the near infrared band. The laser 22 illuminates the missile 16 with a series of short pulses of light 23a. The illuminator laser 22 creates an enhanced image of the missile 16 contained in the reflected radiation 23a, that includes minimal background interference because of its short pulse length image gating. The reflected radiation 23b, in combination with radiation 24 reflected from the target hit spot 20, form an input beam of radiation, indicated generally at 25.