Polarization errors associated with zero-order achromatic quarter-wave plates in the whole visible spectral range

By a combination of quarter-wave plates made of different birefringent mate rials it is possible to produce achromatic quarter-wave plates whose degree of achromatism is dependant on the dispersions of birefringence and on the thicknesses of the individual quarter-wave plates. These waveplates are wi dely used in optical instrumentation and the residual errors associated wit h these devices can be very important in high resolution spectro-polarimetr y measurements. The misalignment of optic axis in a double crystal waveplat e is one of the main source of error and leads to elliptical eigenpolarizat ion modes in the retarder and the oscillation of its orientation according to the wavelength. This paper will discuss, first, how the characteristics of a quartz-MgF2 quarter-wave plate is affected by such a misalignment. A c orrelation with the experiment is then achieved in order to highlight the i nterest of taking a possible tilt error into consideration when doing polar imetric measurements. (C) 2001 Optical Society of America.