Key Calibration Methods for Polarizers in Polarizing Microscopes
Reflective polarizing microscope, also known as mineralogical microscope. In the general optical path of a large microscope, only two polarizing plates need to be added, that is, adding a polarizer in the incident optical path and a polarizer in the observation mirror, to achieve polarized light illumination. In addition to polarizer and analyzer, sometimes a sensitive color plate is also added to detect elliptically polarized light and obtain color polarization.
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, ensuring that the polarized light reflected from the vertical illumination plane glass into the objective lens has the highest 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 strongest, 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.
