We have discussed cryo-electron microscopy several times and noted various efforts and difficulties to introduce simple, stable phase contrast. Recall that phase contrast greatly enhances the signal to noise ratio, and thus makes possible reduced sample dose and concomitant damage.
In this morning’s arXiv preprints one can find Schwartz et al., “Laser control of the electron wave function in transmission electron microscopy”, in which the researchers demonstrate a proof of principle experiment. They establish a standing wave in a Fabry-Perot cavity, and use the spatially varying field to differentially retard the unscattered electrons vs. those electrons scattered by the specimen.
There is an associated US patent application which spells out how a TEM incorporating such a phase device might look.
Schwartz et al., “Laser control of the electron wave function in transmission electron microscopy”, arXiv:1812.04596.
Axelrod et al., “OPTICAL-CAVITY BASED PONDEROMOTIVE PHASE PLATE FOR TRANSMISSION ELECTRON MICROSCOPY”, US Patent Application 20180286631.