Research Paper (postgraduate) from the year 2014 in the subject
Physics - Optics, University of California, Berkeley, language: English,
abstract: The transmission electron microscope is an indispensable tool
in science, with applications across medicine, materials science, and
geology, among others. However, it is limited in its ability to operate
with Zernike phase contrast, a technology commonplace in light
microscopy. Zernike phase contrast can be obtained, but only by using
carbon-film phase plates or similar methods, all of which are
short-lived. Electrons moving close to the speed of light cause damage
as they bombard the phase plates. The phase plates need to be replaced
frequently, which introduces inconsistencies due to variations between
the plates as they are replaced. The purpose of this paper is to
demonstrate the plausibility of utilizing ponderomotive forces within an
optical cavity to achieve phase contrast, creating a laser-based phase
plate, thereby replacing the carbon films and eliminating swapping. We
approach this problem by using a Fabry-Perot to concentrate the laser
power to be able to achieve the necessary electron phase shift with
conventional CO2 lasers. We demonstrate a cavity with finesse of 24000
and numerical aperture of .016, and calculate the laser power needed to
be supplied to be 19W, well within the state of art. These results
demonstrate the practicality of laser-based electron microscope phase
plates.
