A certain birefringent material has refractive indices m and n2 for the two perpendicular components of linearly polarised light passing through it. Therefore wavelengths within the material of the two perpendicular components of linearly polarised light are A1 = Ap/m and A2 = Ap2, where do is the wavelength of the light in a vacuum. If the crystal is to function as a quarter-wave plate, the number of wavelengths of each component must differ by 1/4. Which of the following formulas gives the minimum thickness for a quarter-wave plate? Assume nj > n2. O d = 3Ao / [4(n1-n2)] O d = Ao / [2(nj-n2)] O d = 4ho / [(n1-n2)] O d = Ap / [4(n1-2)]