Someone argues: "For light travelling inside glass of index and meeting an air…

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Wave propagation and light in media · Wave propagation and light in media

What an Instrument Can See, Ch The boundary as a two-port

Problem

Someone argues: "For light travelling inside glass of index

n=1.50

and meeting an air interface at normal incidence, the amplitude transmission coefficient is

t' = \frac{2n}{n+1} = \frac{2(1.50)}{2.50} = 1.20.

Since the transmitted field amplitude cannot be

1.2

times the incident amplitude without creating energy from nothing, either this formula or the Stokes relations that predict it must be wrong." (a) Compute the power reflectance

\mathcal{R}'

and power transmittance

\mathcal{T}'

for this interface (glass to air, normal incidence), using

\mathcal{T}' = (n_{\text{air}}\cos\theta_t/n_{\text{glass}}\cos\theta_i)\,t'^2

with

\theta_i=\theta_t=0

. (b) State whether the claim is correct, and explain the physics that resolves it.

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