Successful ignition of direct drive targets in an IFE power plant requires a reliable system for tracking the location of the target in flight and illuminating it by many separate laser beams with a high degree of precision. As part of a coordinated effort in the High Average Power Laser (HAPL) program, we have developed and tested an interferometric technique for measuring the position and velocity of targets along their axis of motion. The technique involves reflecting light from the moving target and combining it with a reference beam in order to produce interference fringes at a rate corresponding to the movement of the target.

A scaled benchtop experiment has been built and tested to characterize the performance of this technique of axial target tracking. Results are presented here together with recommendations on improvements needed for a full-scale performance demonstration.