Left-circular light of wavelength 590 nm traveling in the z-direction is to be converted into right-circular light by passing perpendicularly through a plate of quartz. The quartz has been cut and polished so that the optic axis is in the y-direction (n_o = 1.5443, n_e = 1.5534) and the face of the plate is the xy-plane.

(a) What is the direction of the fast axis?

(b) How thick, at minimum, should the plate be? Explain your reasoning in detail and draw a diagram.