How to Calibrate Polarizers for Polarizing Microscopes
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 and north-south directions, which are 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 the eyepiece reticle
Generally, it is necessary to check whether the eyepiece reticle is orthogonal and whether it is in the same vibration direction as the upper and lower polarizers. At the same time, select a piece of biotite that has been completely cleaved, move it to the center of the eyepiece reticle, and place the cleavage seam parallel to one of the reticle. record the scale number of the stage, and then turn the stage so that the cleavage seam is parallel to the other cross wire, record the scale number of the stage, the difference between the two scale numbers is 90°, indicating that the cross wire is orthogonal.
(2) Determination and correction of the vibration direction of the lower polarizer
Generally, biotite is used to check the vibration direction of the polarizer, because biotite is a widely distributed transparent mineral, which 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 circle, and observe the color change of biotite, because biotite has the strongest absorption of vibrational light in the cleavage direction, Therefore, 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 upper and lower polarizers
After the direction of the lower polarizer is calibrated, remove the sheet, push the upper polarizer, and observe whether the field of view is completely black, that is, whether it is in a 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.
