Anti-reflective coating effect on total internal reflection? If the surface of prism is coated with an anti-reflective coating, (specifically an index matching, refractive index gradient, or moth-eye structure), and light impinges at a greater than critical angle (i.e. would otherwise be reflected by total internal reflection), at what angle does the light exit the prism?
 A: Answer: you can ignore the coating (assuming monotonic index of refraction); light does not exit if incident ray is beyond critical angle
Reasoning: Snell's Law states
$$n_1 \sin \theta_1 = n_2 \sin \theta_2,$$
where $n_1$ and $n_2$ are indexes of reflection within media $M_1$ and $M_2$, and 
$\theta_1$ and $\theta_2$ are the angle between the normal and the light ray within the respective media.
I presume by "prism" you mean an interface $M_1$ to $M_2$, with $n_1 > n_2$.  
Total internal reflections (TIR) occur when $\sin \theta_2 = \frac{n_1}{n_2}  \sin\theta_1 > 1$, i.e., where transmission would be absurd since there is no real solution for $\theta_2$.
Now consider the case with $3$ media $M_1$, $M_2$, $M_3$ with parallel interfaces. Snell's law becomes
$$n_1 \sin \theta_1 = n_2 \sin \theta_2 = n_3 \sin \theta_3 = \text{constant}.$$
So it doesn't mater what $n_2$ is. As long as $\sin\theta_3 = \frac{\text{constant}}{n_3} > 1$, then $\theta_3$ has no real solution, and light will not enter $M_3$ (in fact, TIR may occur from the $M_1$-$M_2$ interface and never reach $M_3$ in the first place).
We can generalize the above to multiple layers. In the limit we would have a (assumed monotonic) gradient of index of fractions from $n_1$ to $n_2$, for each plane parallel to a common plane (from which the normal is defined).
Now consider a light ray coming from $M_1$ that would normally undergo TIR against $M_2$.  For the gradient case, the light ray would bend and become increasing parallel to the plane, until it encounters a layer $M_i$ with $\frac{n_1}{n_i} \sin \theta_1 = 1$. Thereafter the ray bends back toward $M_1$, effectively undergoing TIR.
(Edit: updated "Answer" section part to match what the question is asking)
