Each imaging principle of metallurgical microscope
1,Bright field, dark field
Bright field of view is the most basic type of microscope observation of samples, in the field of view area of the microscope presents a bright background. The basic principle is that when the light source is illuminated vertically or nearly vertically through the objective lens to the sample surface, the sample surface is reflected back to the objective lens to make its image.
Dark-field illumination and bright field of view is different in that, in the microscope field of view area presents a dark background, bright field of view of the irradiation method for the vertical or vertical incidence, while the dark-field irradiation method for the illumination of the sample through the objective lens outside of the surrounding oblique illumination sample, the sample will play a role in the illumination of the light scattering or reflecting the role of the light scattered or reflected by the sample into the objective lens to make the sample imaging. Dark-field observation, the bright field of view is not easy to observe the colourless, small crystals or light-coloured small fibres, in the dark field of view clearly observed.
2, polarised light, interference
Light is a kind of electromagnetic wave, and electromagnetic wave is a transverse wave, only transverse waves have polarisation. It is defined as the electric vector relative to the direction of propagation in a fixed way vibration of light.
The phenomenon of polarisation of light can be detected with the help of an experimental setup. Take two pieces of the same polarizer A, B, will be the first natural light through the first polarizer A, at this time the natural light also becomes polarized light, but because the human eye can not be identified, so you need a second polarizer B. Polarizer A fixed, polarizer B placed in the same level with A, rotate the polarizer B, you can find that the intensity of the transmitted light with the rotation of the B and the emergence of a cyclic change in light intensity for every 90 ° turn will gradually diminish from the maximum to * dark, the intensity of transmitted light can be found as B rotated and periodic changes in every 90 ° turn from Maximum light intensity will gradually weaken to the darkest, and then turn 90 ° light intensity will be gradually enhanced from the darkest to the brightest, so the polariser A is called a bias initiator, polariser B is called a bias detector.
Interference is the superposition of two coherent waves (light) in the interaction zone is produced by the phenomenon of strengthening or weakening the intensity of light. The interference of light is mainly divided into double-slit interference and thin-film interference. Double-slit interference for two independent light sources are not coherent light, double-slit interference device so that a beam of light through the double-slit into two beams of coherent light, in the light screen through the formation of stable interference fringes. In the double-slit interference experiment, a point on the light screen to the double slit distance difference for an even number of times the half-wavelength, the point of the bright fringe; light screen to a point on the double slit distance difference for an odd number of times the half-wavelength, the point of the dark fringes for the Young's double-slit interference. Thin-film interference for a beam of light reflected by the two surfaces of the film, the formation of two beams of reflected light interference phenomenon called thin-film interference. In thin-film interference, before and after the surface of the reflected light by the thickness of the film to determine the distance difference, so thin-film interference in the same bright fringes (dark fringes) should appear in the thickness of the film in the same place. Because the wavelength of light waves is extremely short, so when thin film interference, the medium film should be thin enough to observe the interference fringes.
