Fluorescence of a two-level atom in a two-dimensional photonic crystal in the vicinity of the saddle point of the photonic band spectrum

Abstract

The fluorescence of a two-level atom embedded into a two-dimensional photonic crystal is considered under the assumption that the electronic transition frequency ω10 is close to the photonic mode frequency ω0 in the saddle critical point of the photonic spectrum. In this case, the density of photonic states has a logarithmic peak, which manifests itself in a considerable rearrangement of the fluorescence spectrum. The Green’s function of the electron-photon system, which contains the description of the dynamics of spectroscopic transitions and the shape of fluorescence spectra, is obtained in the rotating field approximation. Using the Green’s function, the frequency-dependent Lamb shift and the broadening of the atomic transition are calculated. The shape of the fluorescence spectra is studied. At a large oscillator strength of the atomic transition, the fluorescence line splits into two components in the vicinity of the singularity caused by the saddle critical point. This splitting is associated with a specific Fano-type resonance between the discrete spectrum (the atomic states) and the continuum (the dispersion of photons with a saddle critical point). At small detunings δ = ω10-ω0, the components of the fluorescence line have considerably different intensities. As δ increases, the spectral positions of the strong and weak components tend to the frequencies of the atomic transition and the saddle point, respectively. The results obtained show that two-level atoms (or quantum dots) can be used as specific probes of the band spectra of photonic crystals.