Depolarization and principal mueller matrix measured by null ellipsometry

Methods for accurately measuring depolarization and principal Mueller matrix by null ellipsometry are devised. The measurement errors obtained with these methods are analyzed, and methods to correct for the errors are devised. The depolarization spectrum measured directly by null ellipsometry for a sapphire slab agrees excellently with the depolarization spectrum reduced indirectly from the retardance spectrum measured by rotating analyzer ellipsometry and the depolarization spectrum simulated for the retardance spread caused by a finite bandwidth of monochromator [J. Opt. Soc. Am. A 17, 2067 (2001)]. The measured cross-polarized depolarization for the sapphire slab is much smaller than the total depolarization.