15) Consider the interface shown in Fig. -7 below This figure shows the interfac

Question

15) Consider the interface shown in Fig. -7 below This figure shows the interface between air and an anti -reflective thin film coating of MgF2 (Magnesium -fluoride. n = 1.38) that is deposited on top of a 1 mm thick glass substrate with n = 1.52 Assuming that the incident ray has wavelength lambda= 550 nm, calculate the critical thickness required for the antireflective MgF2 coating. Choose from the answers provided below a) tc = 25.2 nm b) tc = 99.64 nm C) tc = 200 nm d) tc = 32.5 nm e) Not possible

Explanation / Answer

The condition for distructive interference is

2nt = L/2

t = L/4n_m = 550 nm/ 4(1.38 ) = 99.64 nm

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