How to correct the polarizing plate of a polarizing microscope?
In operation, the vibration directions of the upper and lower polarizing mirrors of the polarizing microscope should be orthogonal to each other, or in the east-west and north-south directions, respectively, consistent with the horizontal and vertical directions of the crosshair of the eyepiece. 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 crosshair in eyepiece
Generally, it is necessary to check whether the crosshair of the eyepiece is orthogonal and consistent with the vibration direction of the upper and lower polarizing mirrors. At the same time, select a piece of biotite with complete cleavage, move it to the center of the crosshair of the eyepiece, make the cleavage seam parallel to one of the crosshair wires, record the scale number of the stage, and then rotate the stage to make the cleavage seam parallel to the other crosshair. Record the scale number of the stage. The difference between the two degree readings is 90 °, indicating that the crosshair is orthogonal.
2. Determination and correction of the vibration direction of the polarizing mirror
Usually, biotite is used to check the vibration direction of polarizing mirrors, because biotite is a widely distributed transparent mineral. Firstly, find a clear and cleaved piece of biotite, move it to the center of the crosshair of the eyepiece, push out the upper polarizer, rotate the stage once, and observe the color change of biotite. Because biotite absorbs the vibration light in the cleavage direction * strongly, when the biotite color reaches its deepest, the direction of the cleavage seam is the vibration direction of the lower polarizer.
3. Correction of orthogonal polarization of upper and lower polarizing mirrors
After aligning the direction of the lower polarizer, remove the thin film and push it into the upper polarizer to observe whether the field of view is completely black or in an extinction state. If it is all black, it indicates that the vibration directions of the upper and lower polarizations are orthogonal to each other. Otherwise, the polarizer must be calibrated to make the field of view * dark. When rotating, the stop screw of the upper polarizer must be loosened first, calibrated correctly, and then tightened.
