When a birefringent material is placed between crossed polarizers in an optical microscope, light incident upon the material is split into two component beams whose amplitude and intensity vary depending upon the orientation angle between the polarizer and permitted vibration directions of the material.

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This tutorial explores the effects of polarizer rotation on specimen birefringence as observed in a polarized light microscope with a first-order retardation plate inserted between the specimen and the analyzer. To operate the tutorial, first select a specimen from the pull-down menu labeled Choose A Sample. When the tutorial initializes, the specimen will have both focus and illumination intensity values chosen at random. Use the Focus slider to bring the specimen into focus and the Intensity to optimize specimen illumination. The Polarizer Rotation slider can be used to rotate the position of the polarizer from 0 to 180 degrees. Alternatively, the small blue arrow buttons will change polarizer rotation angle in discrete increments. As the polarizer is rotated, interference colors arising from specimen birefringence will change. The polarizer can be toggled into and out of the light path with the Polarizer radio buttons. Use the Reset button to reinitialize the applet to a different set of random values.

Insertion of a first-order retardation plate or compensator between the specimen and the analyzer changes the optical path difference of light passing through the specimen. Compensator plates providing a retardation of one entire wavelength (550 nanometers) are termed sensitive tint or first-order red plates. These quartz plates can be utilized to determine the sign of birefringence exhibited by the specimen.