Figure 5
Temperature-induced mode switching in the cup-cavities.
(a) SEM and μ-CL images (orthogonal view) of the same InN crystal recorded at 5 K and 300 K showing the change of the dominant mode type from azimuthal to radial. (b) The simulated distributions of electromagnetic field intensity, as seen in the plane and cross-section of the crystal, shown together with the schematic shape used in these simulations. (c) Variation of the refractive index derived from the fitting of the WGMs at low (squares) and room (triangles) temperatures; the dotted lines is their polynomial fitting; the solid lines indicate the index dependencies derived from the integral optical spectra. (d) Teraherz spectrum shown together with the peak of the NIR emission comprising two unstable WGM-related lines. The energy scale is taken as 
, where 
is the peak energy of the first line for the NIR emission, while for the THz band 
.
