Making use of the expression I(y) = I 0 e -y [4.78] for an absorbing medium, we define a quantity called the unit transmittance T

Making use of the expression

I(y) = I₀e^-αy             [4.78]

for an absorbing medium, we define a quantity called the unit transmittance T₁. At normal incidence, Eq. (4.55), T = I_t/I_i, and thus when y = 1, T₁ = I(1)/I₀. If the total thickness of the slides in the previous problem is d and if they now have a transmittance per unit length T₁, show that

T_t = (1 - R)^2N(T₁)^d