A holographic biprism as a perfect energy filter?

It has often been stated that a holographic biprism represents a near perfect energy filter and only elastically scattered electrons can participate in the interference fringes. This is based on the assumption that the reference wave does not contain inelastically scattered electrons. In this letter we show that this is not exactly true because of the delocalised inelastic interaction of the reference wave with the sample. We experimentally and theoretically show that inelastic scattering plays a role in the fringe formation, but it is shown that this contribution is small and can usually be neglected in practice. -- Research highlights: → It is common wisdom that in electron holography only elastic scattering contributes to the fringe pattern. → We demonstrate experimentally that this concept is wrong. → We show theoretically that by including delocalised inelastic scattering also inelastically scattered electrons contribute to the fringe pattern. → The effect is found to be small and inelastic events with energy losses above 5 eV should not considerably influence the reconstructed wave in conventional off-axis electron holography.