  In this paper we explore the desirability of a transmission electron
microscope in which the phase of the electron wave can be freely controlled. We
discuss different existing methods to manipulate the phase of the electron wave
and their limitations. We show how with the help of current techniques the
electron wave can already be crafted into specific classes of waves each having
their own peculiar properties. Assuming a versatile phase modulation device is
feasible, we explore possible benefits and methods that could come into
existence borrowing from light optics where so-called spatial light modulators
provide programmable phase plates for quite some time now. We demonstrate that
a fully controllable phase plate building on Harald Rose's legacy in aberration
correction and electron optics in general would open an exciting field of
research and applications.
