9. (a) A glass block (n = 1.50) is separated by a thin air-gap, a tenth of a wavelength wide, from a second glass block
with n = 1.60. Light striking the first interface at 60 degrees
reaches the second glass block due to frustrated total
internal reflection. Determine the power transmittance for an s-type electric field.
(b) What is the penetration length when light strikes the first interface exactly at the critical angle?