How to correct the polarizer of a polarizing microscope?
During operation, the vibration directions of the upper and lower polarizers of a polarizing microscope should be orthogonal to each other, or in the east-west and north-south directions, and should be consistent with the horizontal and vertical directions of the eyepiece crosshairs. 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 calibrated during operation.
1. Detection of eyepiece crosshairs
Generally, you need to check whether the eyepiece crosshairs are orthogonal and whether they are consistent with the vibration direction of the upper and lower polarizers. At the same time, select a piece of biotite with extremely complete cleavage, move it to the center of the eyepiece crosshairs, and place the cleavage seam parallel to one of the crosshairs. wire, record the number of scales on the object stage, then rotate the object stage so that the cleavage seam is parallel to the other cross hair, record the number of scales on the object stage, the difference between the two scale numbers is 90°, indicating that the cross wires are orthogonal.
2. Determination and correction of the vibration direction of the lower polarizer
Biotite is generally used to check the vibration direction of the polarizer, because biotite is a widely distributed transparent mineral. First, find a piece of biotite that is cleaved and clear, move it to the center of the eyepiece crosshair, push out the upper polarizer, rotate the stage for one turn, and observe the change in the color of the biotite, because biotite has the strongest absorption of vibrational light in the direction of cleavage. Therefore, when the color of biotite reaches the deepest level, the direction of the cleavage seam is the vibration direction of the lower polarizer.
3. Orthogonal correction of upper and lower polarizers
After correcting the direction of the lower polarizer, remove the sheet, push in the upper polarizer, and observe whether the field of view is completely black or in a matted 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 to make the field of view the darkest. When rotating, you must first loosen the stop screw of the upper polarizer, and then tighten it after correcting it.
