Add information regarding performance gains and dipole polarization t…

…o cylindrical extraction-efficiency tutorial (#2815)

* add information regarding performance gains and polarization state to cylindrical extraction-effciency tutorial

* mention that the number of independent dipole simulations is the same in cylindrical and 3D coordinates

doc/docs/Python_Tutorials/Near_to_Far_Field_Spectra.md

@@ -660,6 +660,10 @@ if __name__ == "__main__":
 
 [Tutorial/Radiation Pattern of a Disc in Cylindrical Coordinates](Near_to_Far_Field_Spectra.md#radiation-pattern-of-a-disc-in-cylindrical-coordinates) demonstrated the procedure for computing the radiation pattern of a *single* dipole (actually a "ring" current source with angular dependence $e^{im\phi}$). [Tutorial/Nonaxisymmetric Dipole Sources](Cylindrical_Coordinates.md#nonaxisymmetric-dipole-sources) described the method for modeling a point dipole at $r > 0$ in cylindrical coordinates using a Fourier-series expansion of the fields in $\phi$. [Tutorial/Extraction Efficiency of a Light-Emitting Diode](Local_Density_of_States.md#extraction-efficiency-of-a-light-emitting-diode-led) described the procedure for computing the extraction efficiency of a dipole at $r = 0$. These three demonstrations can be combined to compute the extraction efficiency for a point dipole *anywhere* in the cylindrical cell. Computing the extraction efficiency of an actual light-emitting diode (LED), however, involves a collection of spatially incoherent dipole emitters. [Tutorial/Stochastic Dipole Emission in Light Emitting Diodes](Custom_Source.md#stochastic-dipole-emission-in-light-emitting-diodes) described a method for computing the emission of a collection of dipoles using a series of single-dipole calculations and then averaging the emission profiles in post processing. The example used a 2D simulation involving a 1D binary grating (or photonic crystal). This tutorial demonstrates how this approach for modeling spatially incoherent dipoles can be extended to cylindrical coordinates for structures with rotational symmetry.
 
+Note: in the case of a disc, the set of dipoles within the quantum well (QW) which spans a 2D surface only needs to be computed along a line. This means that the number of single-dipole simulations necessary for convergence is the same in cylindrical and 3D Cartesian coordinates.
+
+Note: for randomly polarized emission from the QW, each dipole requires computing the emission from the two orthogonal "in-plane" polarization states of $E_r$ and $E_\phi$ separately and averaging the results in post processing. In this example, only the $E_r$ polarization state is used.
+
 The example uses the same setup as the [previous tutorial](#radiation-pattern-of-a-disc-in-cylindrical-coordinates) involving a dielectric disc above a lossless-reflector ground plane. The dipoles are arranged on a line extending from $r = 0$ to $r = R$ where $R$ is the disc radius. The height of the dipoles ($z$ coordinate) within the disc is fixed. The radiation pattern $P(r,\theta)$ for a dipole at $r > 0$ is computed using a Fourier-series expansion in $\phi$. The *total* radiation pattern $P(\theta)$ for an ensemble of incoherent dipoles is just the integral of the individual dipole powers, which we can approximate by a sum:
 
 $$P(\theta) \approx \int_0^R P(r,\theta) s(r) 2\pi rdr = \sum_{n=0}^{N-1} P(r_n,\theta) s(r_n) 2\pi r_n \Delta r$$,