A light beam with a wavelength of $600$nm is incident on calcite in a direction perpendicular to the optical axis $($where n is parallel $=1\mathrm{.}43,$ n is perpendicular $=1\mathrm{.}55).$ What are the requirements for making a half$-$wave plate and a quarter$-$wave plate? What is the minimum thickness of the wave plate that should be designed?