To correct the polarizer of a polarizing microscope, follow these steps
In actual 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 or 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
Check whether the eyepiece crosshairs are orthogonal and 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 crosshair, place the cleavage seam parallel to one of the crosshairs, record the number of scales on the object stage, and then rotate the object stage so that the cleavage seam is parallel to one of the crosshairs. On the other crosshair, record the scale number of the object stage. The difference between the two scale numbers is 90°, indicating that the crosshairs are orthogonal.
2. Determination and correction of the vibration direction of the lower polarizer
Biotite is used to check the vibration direction of the polarizer 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 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 its 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 corrected, remove the sheet, push in the upper polarizer, 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, rotate the upper polarizer until the field of view reaches the darkest level. When rotating, you must first loosen the stop screw of the upper polarizer, and then tighten it after correcting it.
