The plot shows the total electric field intensity $|E_{\text{tot}}|^2$ as a function of $z_0$. You can observe the oscillating behavior caused by the interference of the two waves, with peaks at constructive interference points and zero intensity at destructive interference points, such as $z_0 = \frac{\lambda}{2}$.

Summary:

1. The net Poynting vector at $z_0 = \frac{\lambda}{2}$ is zero, indicating complete destructive interference.
2. The plot of $|E_{\text{tot}}|^2$ as a function of $z_0$ shows constructive and destructive interference patterns, with maximum values where the waves reinforce each other and minimum values where they cancel out.

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Would you like further details or have any questions? Here are some related questions to consider:

1. What happens to the Poynting vector at points of constructive interference?
2. How does the wavelength affect the interference pattern?
3. Can interference occur in non-planar wave geometries?
4. What role does the phase difference play in this type of interference?
5. How would this analysis change if the amplitude of the two waves were different?

Tip: Interference patterns are sensitive to both the phase and amplitude of the waves involved, leading to a rich variety of behaviors depending on their relative values.