Heat maps displaying the transverse electric polarisation for a wide range of propagation angles and different combinations of β_p and β_e/β_p as a function of the wavenumber in units of ${\rho }_{\mathrm{L}}^{-1}$ and for different combinations of β_p and kρ_p as functions of β_e/β_p. The white lines indicate the contour of Re[iE_x/E_y] = 0 and black lines represent contours of characteristic values of −γ/Ω_p, where γ is the imaginary part of the wave frequency.