n₁ sin θ₁ = n₂ sin θ₂; total internal reflection at θ_c = sin⁻¹(n₂/n₁); evanescent wave in forbidden medium (frustrated TIR).
n₁ sin θ₁ = n₂ sin θ₂; total internal reflection at θ_c = sin⁻¹(n₂/n₁); evanescent wave in forbidden medium (frustrated TIR).