0$ $nm$. Gaussian beam incidence with $W=0000$ $nm$. \[fig:prb0\](a): $\protect\lambda =000$ $nm$ (on resonance), $\protect\theta_ o=0^o$. \[fig:prb0\](b): $\protect\lambda =000$ $nm$ (on resonance), $\protect\theta_o=00^o$. \[fig:prb0\](c): $\protect\lambda =000$ $nm$ (off resonance), $\protect\theta_o=00^o$. \[fig:prb0\](