Eliminating effects of biprism drift in electron holography

Abstract

Reconstruction of phase images from off-axis electron holograms recorded in a field-emission TEM was for many years a tedious and time-consuming process. The advent of digital imaging systems and ever-faster desktop computers has recently resulted in processing times of a few seconds for a useful phase reconstruction. However, a goal of the “holographer” has been to view the phase images essentially in “live-time”, that is, at least at a few frames per second. This enables effective observation of phase change, through “a window to the phase world,” while the sample is being searched. Chen et al. used a mixture of digital and analog techniques to obtain phase images at nearly TV scan rates. Because optical lens systems provide the fast Fourier processing required for phase reconstructions, their geometry allows phase images to be displayed while the sample is being moved and/or timedependent specimen changes are occurring. Voelkl et al. have described a purely digital system for phase reconstructions from electron holograms that provides several phase images per second, and has several advantages over the mixed system. The refresh rate is presently limited more by the readout time of the slow-scan digital camera than by the computational time of the computer.