Calibration of the MgF2 Biplate Compensator Using a Straight-Through Ellipsometer

Zero order MgF2 compensators are extensively used in deep ultra-violet(DUV) broadband optical instruments. This biplate compensator is made by two MgF2 wave plates. For DUV broadband spectroscopic ellipsometers, the misalignment between the principal axes of the two MgF2 wave plates must be carefully calibrated for the phase-retardance in order for this kind of compensator to be used in a high accuracy measurement. In this paper, we present a novel calibration method for such biplate compensator using a straight-through PCRA (polarizer-rotating compensator-analyzer) ellipsometer. The theoretical formulae of the biplate compensator and the calibration method are derived by means of Jones matrix calculus. The experimental result for characterizing a commercial zero-order MgF2 biplate compensator is presented. This method can be applied to multi-wave plate compensators, for example, achromatic and super achromatic compensators.