Holographic system for interactive target acquisition and tracking

Abstract

A holographic laser target acquisition and tracking system with aberration compensation including a detector array, a master-oscillator (MO), a hologram processor, a spatial light modulator (SLM) and a slave oscillator which is referred to as a Holographic Interactive Tracker system. The operation of the system consists of two steps. In step one, an acquisition step, a diverging laser beam (acquisition beam) from the laser oscillator is transmitted to a target 38. The beam divergence is typically much larger than the target angular extent. A fraction of the diverging energy intercepted by the target is returned, as a beam or as diffuse radiation, and collected by a receiver optic. This target return is interfered with a master oscillator beam from the MO on the electronic detector array, thereby forming an electro-optic hologram. The detector array is read out pixel by pixel and applied to the hologram processor which enhances the hologram by subtracting out the d.c. component. The hologram is processed, and the resulting pattern is transferred pixel by pixel to the spatial light modulator (SLM) where the electronic hologram is written in as a phase hologram. In step two, an engagement step, a beam from the same or a separate laser oscillator is reflected off the SLM. The SLM output consists of multiple beams (orders) of radiation, one of which is the conjugate of the target return radiation. Through the properties of phase conjugation, this beam retraces the target return path while, at the same time, the wavefront distortions are undone, resulting in maximum energy delivery to the target. By repeating acquisition and engagement steps one and two as the target moves, the system automatically tracks it.