Jerold L. Jacoby

Laser beam active tracking for specular objects to fractions of λ/D

Width modulation of a laser beam produces a far-field diffraction pattern rich in harmonics of the width-modulating frequency as a function of lateral distance from the beam center. A small specular target samples this field, and reflected radiation from the target can be used to close a tracking loop. The concept can be used either as a stand-alone system or as a high-precision addition to conical scan. For transmitter aperture D, the laboratory demonstration yielded crisp lockup on a specular target with an angular track precision of 0.15 λ/D at moderate SNRs.