A magnifying lens for velocity map imaging of electrons and ions

We have designed and implemented an electrostatic lens that magnifies the images of an existing velocity map imaging apparatus up to a factor of 20. The lens can be used to vary the magnification while keeping the field strength in the interaction region constant. For the region of interest where magnification is required (low energy ions or electrons, in a high external field) the lens does not add any observable aberrations to the imaging. We have characterized the performance of the lens using the imaging of slow photoelectrons.