Slice imaging: A new approach to ion imaging and velocity mapping

In this article we present a new approach to the already popular methods of ion imaging and velocity mapping. The novelty of this approach is that the speed and angular distributions are measured directly from the images without the need of inverse Abel transformation as in the conventional approaches. This is achieved by using delayed pulsed extraction of the ions following photodissociation and positioning of the nascent products. Delayed pulsed extraction causes a sufficient velocity spread in the ion cloud such that the time width of the ion packet at the detector is on the order of 500 ns. By using a narrow detector time gate (<40 ns) we are able to image only the center slice of the ion packet. The result is equivalent to that obtained by conventional methods using the inverse Abel transform, however, the artificial noise introduced by this transform is eliminated. The energy resolution of the new approach is at least comparable to that achieved with the velocity mapping technique. (C) 2001 American Institute of Physics.