Polarization correction method for polarizing microscope
In practical operation, the vibration directions of the upper and lower polarizers of the polarizing microscope should be orthogonal to each other, or in the east-west and north-south directions, each consistent with the transverse and longitudinal directions of the cross hairs of the eyepiece. Sometimes only one lower polarizer is used for observation, and the vibration direction of the lower polarizer must be determined, so the polarizer must be corrected during operation.
(1) Inspection of cross hairs in eyepieces
Generally, it is necessary to check whether the cross hairs of the eyepiece are orthogonal and consistent with the vibration direction of the upper and lower polarizers. At the same time, select a piece of black mica with complete cleavage and move it to the center of the cross hairs of the eyepiece. Place the cleavage seam parallel to one strand of the cross hairs, record the number of scales on the loading stage, and then turn the animal stage to make the cleavage seam parallel to another cross hairs. Record the number of scales on the loading stage, and the difference between the two notches is 90 °, indicating that the cross hairs are orthogonal.
(2) Determination and Correction of the Vibration Direction of the Lower Polarization Mirror
Generally, black mica is used to check the vibration direction of the polarizer, because black mica is a widely distributed transparent mineral that has characteristics under unipolar light. Firstly, find a piece of cleavage and clear biotite, move it to the center of the eyepiece cross hair, push out the upper polarizer, rotate the stage for one cycle, and observe the color change of the biotite. Because biotite absorbs the strongest vibration light in the cleavage direction, when the color of the biotite reaches * depth, the direction of the cleavage seam is the vibration direction of the lower polarizer.
(3) Correction of orthogonality between upper and lower polarizers
After adjusting the direction of the lower polarizer, remove the thin film and push it onto the upper polarizer to observe whether the field of view is completely black, i.e. whether it is in an extinction state. If it is all black, it indicates that the vibration directions of the upper and lower polarized light are orthogonal to each other. Otherwise, the upper polarizer must be corrected by rotating it until the field of view reaches its darkest point. When rotating, the stop screw of the upper polarizer must be loosened first, calibrated, and then tightened.
