How to Calibrate a Polarizing Microscope's Polarizer
In actual operation, the vibration directions of the upper and lower polarizers of the polarizing microscope should be orthogonal to each other, or the east-west or north-south directions, respectively consistent with the horizontal and vertical directions of the eyepiece reticle. 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. Detection of eyepiece reticle
It is necessary to check whether the reticle of the eyepiece is orthogonal and whether it is consistent with the vibration direction of the upper and lower polarizers. At the same time, choose a piece of biotite that has been completely cleaved, move it to the center of the eyepiece crosshair, and make the cleavage seam parallel to a thread of the crosshair, record the scale number of the stage, and then turn the stage to make the cleavage seam parallel to For the other crosshair, record the scale number of the objective stage, the difference between the two scale numbers is 90°, indicating that the crosshair is orthogonal.
2. Determination and correction of the vibration direction of the lower polarizer
The use of biotite to check the vibration direction of the polarizer is because biotite is a widely distributed transparent mineral that is very characteristic under single polarized light. First find a piece of biotite that is cleaved and clear, move it to the center of the reticle of the eyepiece, push out the upper polarizer, rotate the stage for a week, and observe the color change of biotite, because biotite has the strongest absorption of vibration light in the direction of cleavage , so when the color of biotite reaches the deepest, the direction of the cleavage seam is the vibration direction of the lower polarizer.
3. Orthogonal correction of the upper and lower polarizers
After the direction of the lower polarizer is calibrated, remove the sheet, push the upper polarizer in, and observe whether the field of view is completely black, that is, whether it is in an extinction state. If it is completely black, it means 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 turning, the stop screw of the upper polarizer must be loosened first, and then tightened after calibration.
