where ℏ ℏ ω ω is the probe-photon energy, F λ λ is the oscillator strength of the exciton state λ λ , and γ γ λ λ is the dephasing constant associated with the exciton state λ λ . For a phenomenological description, γ γ λ λ can be used as a single fit parameter, i.e., γ γ λ λ → → γ γ . However, a full microscopic computation generally produces γ γ λ λ ( ω ω ) that depends on both exciton index λ λ and photon frequency. As a general tendency, γ γ λ λ ( ω ω ) increases for elevated E λ λ while the ω ω dependence is often weak.