A Babinet compensator is positioned at 45° between crossed linear polarizers and is being...

A Babinet compensator is positioned at 45° between crossed linear polarizers and is being illuminated with sodium light. When a thin sheet of mica (indices 1.599 and 1.594) is placed on the compensator, the black bands all shift by  of the space separating them. Compute the retardance of the sheet and its thickness.