The prisms may now be rotated in their holders until the scale readings are 0 [+ or -] 180[degrees], and 90 [+ or -] 180[degrees], and the alinement is complete.
Fortunately, with certain assumptions, even in this case alinement may be achieved quite accurately.
It will be noticed that this point is not on the line P = A+[pi]/2 However, if [chi] = 0, then the deepest minimum occurs at zero azimuth for both P and L, and thus either method of alinement may be used if the light is perfectly plane polarized.
A step-by-step procedure for alinement of the ellipsometer is as follows:
This procedure eliminates alinement errors due to ellipticity produced by the polarizer.