How to calibrate the polarizer of a polarizing microscope?

　　(1) Detection of eyepiece crosshairs

Generally, it is necessary to check whether the crosshairs of the eyepiece are orthogonal and whether they are consistent with the vibration direction of the upper and lower polarizers. At the same time, select a very completely cleaved biotite and move it to the center of the crosshairs of the eyepiece, and make the cleavage slit parallel to one of the crosshairs. For silk, record the number of scales on the download stage, and then turn the animal platform to make the cleavage seam parallel to the other crosshairs, and record the number of scales on the download stage. The difference between the two scales is 90°, indicating that the crosshairs are orthogonal.

　　(2) Determination and correction of the vibration direction of the polarizer

　　 Generally, biotite is used to check the vibration direction of the lower polarizer. This is because biotite is a widely distributed transparent mineral, which is very characteristic under single polarized light. First find a piece of cleavage and clear biotite, move it to the center of the eyepiece crosshairs, push out the upper polarizer, rotate the stage for a week, and observe the color change of the biotite, because the biotite absorbs the strongest vibrational light in the cleavage direction. Therefore, when the biotite color reaches the deepest, the direction of the cleavage seam is the vibration direction of the lower polarizer.

　　(3) Correction of orthogonal upper and lower polarizers

　　 After correcting the direction of the lower polarizer, remove the sheet and push the upper polarizer to observe whether the field of view is completely black, that is, whether it is in the extinction state. If it is completely black, it indicates that the vibration directions of the upper and lower polarized lights are orthogonal to each other. Otherwise, the upper polarizer must be corrected, that is, turn the upper polarizer to make the field of view reach the darkest. When rotating, the stop screw of the upper polarizer must be loosened first, and then tightened after calibration.