Armed with a wavelength$-$optimized emitter, you test out its performance by applying a current and using an infrared viewer to see the beam. You notice that it has a constant radiance at all viewing angles at a drive current of $40$ mA and lower. However, above $40$ mA the radiance drops dramatically at angles larger than $5$ from the normal vector to the emitting surface.

a$)$ What is the emission$/$operational mode of the semiconductor device below $40$ mA$?$

b$)$ What is the emission$/$operational mode of the semiconductor device above $40$ mA$?$

c$)$ Further testing shows that the overlap factor of your propagating mode in the semiconductor device is $80\%$ and that the mode has a propagation loss of $2\mathrm{.}7$ cm$.$ Assuming the $300$m long device has two reflectors with equal reflectance and a gain vs$.$ current relationship of g$($I$)=0\mathrm{.}8($cm$/$mA$),$ what is the reflectance of the two cavity mirrors?