The minimum thickness = 996.4 A

 alpha = 3.142 for MgF2 and 3.369 for lucite

 For MgF2 : I = (0.000000)*I_0

 For lucite : I = (0.052)*I_0

For Lucite : (0.052)*I_0 , indicates 5.2 percentage  of the incident light is reflected ,so it is less suitable for coating. 