What is reflected source illumination and how does it function in metallurgical microscopy?

Reflected light illumination is an illumination technique used in metallurgical microscopy to observe opaque samples such as metals and alloys. Its working principle is to irradiate the light emitted by the light source to the sample surface through the objective lens, and then reflect it from the sample surface back to the objective lens, and finally form an image for observation and analysis. This process emits light through a light source, and the light is guided to the objective lens through a semi-transparent mirror or other optical elements, and then emerges from the objective lens and illuminates the sample surface. When light strikes the surface of an opaque metal sample, it is reflected back to the objective lens. The objective lens collects the reflected light and focuses it into the microscope's imaging system, thereby presenting an image of the sample's microstructure.

The role of reflected light source illumination in metallurgical microscopes is mainly reflected in the following aspects. First, it enables efficient observation of opaque samples such as metals and many other materials that cannot be observed with transmitted light. Secondly, it can significantly improve the contrast and resolution of sample surface details, making microstructures such as grains, phase boundaries, and precipitates clearer. In addition, the reflected light source illumination supports multiple observation modes, such as bright field, dark field, differential interference (DIC) and polarized light, to adapt to different types of metal analysis needs. It is also capable of detailed observation and analysis of surface defects of metal samples, such as cracks, holes and corrosion, as well as surface treatment effects, such as coating quality and polishing effect. In metallurgical research, through reflected light source illumination, the phase transformation process and grain structure changes of metals under different processing conditions can be analyzed.