Fig. 4

Heat engine efficiency. Efficiency as a fraction of the Carnot efficiency for an exciton heat engine. Results are shown as functions of the spectral chirp (a, horizontal axes) and the pulse area (Θ₀, vertical axes) of the driving pulse used for the heat absorption stroke. The panels correspond to different values of the detuning, δ, and unchirped pulse duration, τ₀. a δ = 0 ps⁻¹, τ₀ = 2 ps⁻¹. b δ = 2.5 ps⁻¹, τ₀ = 2 ps⁻¹. c δ = 0 ps⁻¹, τ₀ = 0.5 ps⁻¹. d δ = 2.5 ps⁻¹, τ₀ = 0.5 ps⁻¹