A glass lens (nglass = 1.52) has an antireflection coating of MgF2 (n = 1.38).

(a) For 545-nm light, what minimum thickness of MgF2 will cause the reflected rays R2 and R4 in FIGURE 28-50 to interfere destructively, assuming normal incidence?

(b) Interference will also occur between the forward-moving rays R1 and R3 in Figure 28-50. What minimum thickness of MgF2 will cause these two rays to interfere constructively?

In figure 28-50

Incident light R2 R1 R4 R3 Glass MgF2 Air (n = 1.52) (n = 1.00) (n = 1.38)