Collective atomic effects in resonance fluorescence: The "scaling factor"

In this Comment we study the resonance fluorescence of a system of two atoms separated by an arbitrary distance $R$ in an on-resonance laser field. The steady-state spectrum is calculated in the strong-field limit both for negligible and for non-negligible dipole-dipole interaction. The singlet state of the system is included throughout, even for small interatomic separations. We show that the so-called "scaling factor," or the enhancement of the integrated fluorescence by $N$ atoms (above the expected factor of $N$), predicted in the literature by many authors, does not, in fact, exist.