Differential Interferometric Phase Contrast Metallographic Microscope Nomarski Prism Design

Bright field, dark field, polarization and differential interference contrast (DIC) microscopy can be used in metallographic microscope, the most powerful one is DIC microscopy. DIC microscopy makes eyes or photographic materials detect the light intensity difference because of the optical path difference caused by tiny height difference on sample surface by using two beam interference of polarized light. It can increase the contrast between the micro organization details and enhance the resolution of the microscope to nanometer scale.The key technology of the DIC microscopy is Nomarski prism’s design. When a beam passes through a Nomarski prism, it will be divided into two beams which are ordinary light and extraordinary light. They have the same direction of propagation and their vibration direction are perpendicular to each other. They produce a very small angle which is less than the resolution limit of microscope, and at the same time, an appropriate optical path difference can be generated. In such circumstances, object organization edge part shows in the form of light intensity difference and shadow effect. The differential interference contrast microscopy is peculiar sense in metallographic microscope.This paper introduces the imaging principle of metallographic microscope and factors which influence the aberration and the image quality, the structure of optical, mechanical, and lighting system, the whole debugging process and some problems needed to pay attention to. This paper focuses on the basic principle of the DIC microscopy as well as the basic conditions of DIC microscopy. The improved Nomarski prism has been designed according to typical prisms, and parameters, such as beam splitting angle and coherent surface, which have been calculated and simulated with MATLAB. The design of the prism has been completed by the use of CAD. According to the results of DIC microscope, it is confirmed that the DIC system design scheme is correct, experimental device is feasible and can be used to realize batch production.