Compensated laser resonant fluorescence beam sensing device for neutral particle beams

Abstract

A device for determining the direction of a neutral particle beam relativeo a reference direction is provided. The technique of laser resonant fluorescence is used. Measurements are made near the doppler free angle and a direct view prism means is used for automatically compensating for small drifts in the laser frequency is used to insure that the most accurate alignment results are obtained even with laser frequency changes.

We claim: 
     
       1. In a system where first and second energy beams are intersecting at an angle at an intersection so as to cause resonant fluorescence in accordance to factors including the magnitude of said angle and the frequency of said first beam, the improvement comprising a direct view prism positioned between said first beam and the intersection of said beams for causing a compensating change in the magnitude of said angle in accordance to a change in the frequency of said first beam. 
     
     
       2. A system as set forth in claim 1 wherein said first beam is a laser beam generated by a laser means and said direct view prism is positioned such that at a predetermined frequency, said first beam will pass through said prism unchanged in angle and at frequencies different from said predetermined frequency will exit said direct view prism at a changed angle and cause the angle of intersection of the two beams to be changed such that resonant fluorescence will still occur barring any change in the factors other than frequency. 
     
     
       3. A system as set forth in claim 2 further comprising a turning mirror positioned between said laser and said direct view prism so that the angle of said turning mirror gives an indication of the angle at which said first beam at said predetermined frequency would intersect said second beam regardless of the amount of shift in the angle presented by the direct view prism due to frequency change of said first beam. 
     
     
       4. A system as set forth in claim 3 further comprising photon detectors located in the vicinity of said intersection so as to generate an output upon the detection of the resonant fluorescence. 
     
     
       5. A system as set forth in claim 4 in which a third beam is located orthogonally to said first beam, and further turning mirrors photon detectors and direct view prisms are provided in the same manner as in the said first beam so as to provide position on said second beam.