Applications of electron holography

The development of a coherent field-emission electron beam has facilitated practical applications of electron holography. This paper reviews this field of growing importance, making special reference to the application of electron holography to current technological problems. It is seen that the phase distribution of an electron wave function transmitted through a specimen can be observed as an interference micrograph, thus providing considerable information about the microscopic distribution of electromagnetic potentials. For example, a magnetic sample's contour fringes directly indicate its magnetic lines of force. These fringes can also show the equipotential lines of an electric sample and thickness contours of a homogeneous specimen. Holographic techniques can be effectively employed to improve the accuracy of phase measurements up to an order of $\frac{2\pi }{100}$. This opens the way for use of electron holography as a high-precision measurement method that can cast light on wide regions of the microscopic world pertinent to both basic science and practical industry.