Adjustment of the Polarizing Light Assembly for Polarizing Microscopes
1, Adjustment of Polarizing Mirror Position: Polarizing mirrors are generally installed in a rotatable circular frame and adjusted by turning them with a handle. The purpose of adjustment is to make the polarized light emitted from the polarizing mirror horizontal, to ensure that the polarized light reflected by the vertical illumination plane glass entering the objective lens has a high intensity and remains linearly polarized light. The adjustment method is to place the polished and uncorroded stainless steel sample (optical homogenizer) on the stage, remove the polarizer, only install the polarizer, observe the intensity of the reflected light on the polished surface of the sample from the eyepiece, rotate the polarizer, and the intensity of the reflected light changes. When the reflected light is strong, it is the correct position of the polarizer vibration axis.
2, Adjustment of polarizer position: After adjusting the polarizer position, install the polarizer and adjust its position. When a dark extinction phenomenon is observed in the eyepiece, it is the position where the polarizer is orthogonal to the polarizer. In practical observation, the polarizer is often deflected at a small angle to increase the contrast of the microstructure. The deflection angle is indicated by the scale on the dial. If the polarizer is rotated 90 degrees in an orthogonal position, the vibration axes of the two polarizers will be parallel, and the effect will be the same as under normal lighting. Many metallographic microscopes have already fixed the direction of the polarizer or the vibration axis of the polarizer at the factory, as long as the position of the other polarizer is adjusted.
3, Adjustment of the center position of the stage: When using polarized light to identify phases, it is often necessary to rotate the stage 360 °. In order to ensure that the observation target does not leave the field of view when the stage rotates, the mechanical center of the stage must be adjusted to coincide with the optical system axis of the microscope before use. Usually, adjustments are made through the centering screws on the stage.
4, Color under polarized light illumination (color polarization): The above is a discussion of the situation under monochromatic polarized light illumination. If the influence of polarized light wavelength is taken into account, that is, using white polarized light illumination will produce color. When observing orthogonal polarized light in a metallographic microscope, inserting a sensitive color plate (currently a full wave plate with λ=5760nm is commonly used) in the optical path will result in different colors of anisotropic metal grains. When observing isotropic metals, without adding sensitive color chips, there will still be different colors, but the colors are not rich. After adding a full wave plate, the colors become vivid. By rotating the stage or sensitive color plate, the color of the grains changes, mainly due to the interference of polarized light. Polarized microscopes, like regular microscope illumination, are divided into two types of illumination: bright field illumination and dark field illumination. Polarized microscope is a type of microscope used to study so-called transparent and opaque anisotropic materials. Any substance with birefringence can be clearly distinguished under a polarizing microscope. Of course, these substances can also be observed using staining methods, but some are impossible and must be observed using a polarizing microscope.
