Mechanically propelled molecular beams: techniques and opportunities

Abstract

The speed of propulsion of molecular beams by a rotating shaft has been extended beyond 2 km s -1 by the use of fibre-reinforced material; the optimization of the design is briefly reviewed. Two such rotors, synchronized and phased-locked to within 1° of arc, enable oppositely directed beams to collide with a fourfold increase of available energy, up to about 4 × 10 -2 eV per unit of molecular mass. The main constructional and operational features of the apparatus are described; it has been used in a preliminary search for photons from colliding atoms of mercury. The full exploitation of the double-rotor system will depend on the understanding and control of the spreads in direction, in speed and in time of the molecules in each pulse. The progress of pulses is therefore followed by elementary calculations that show that the beam intensity could be much higher than has hitherto been used. The double-rotor arrangement can also provide time-of-flight measurement in a manner not available to single-rotor propulsion or to beams from fixed sources. This is applicable when the instant of a collision can be precisely determined, for example by the timing of photon emissions. In such, admittedly exceptional, circumstances it would give improvement both in energy resolution and in the efficiency with which information is gathered.