Figure 4: (a) Real and (b) imaginary parts of the complex optical conductivity (solid line) of a superconductor as a function of frequency based on generalized Mattis-Bardeen theory [27] for and a finite scattering rate [28]. Dashed lines disentangle the contributions of both the thermal electrons [first term in (1) and dashed arrows in Figure 3(b)] and photon-activated electrons [second term in (1) and solid arrow in Figure 3(b)] to the conductivity. Insets of (a) and (b) show and for different temperatures ( = 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, and 0.1) and scattering rates ( = 40, 20, 4, 2, 0.8, 0.4, and 0.04 , respectively. (Used parameters , K, and ) (after [72]).