Pure Superradiance from the Inverted Levels of Spin Triplet States Coupled to Resonator

The theory of the pure superradiance (SR) from the coupled system “inverted transition of the spin-triplet states (STSs) plus resonator” is developed in the case, when the linewidth of the magnetic resonance of the transition is less than the bandwidth of the resonator. The magnetic resonance of the STS transition is described with the help of the single transition operators. The initial state of spins is assumed incoherent. The interaction of spins with a resonator is taken into account in the frames of the semiclassical model. If the initial negative polarization of spins is above the threshold, this interaction leads to the coherent motion of spins and to the delayed pulse of the radiation from the resonator, the power of which is proportional to the radiator number squared─i.e., to the pure SR. The parameters of SR are calculated: the time dependence of the pulse power, the delay time, the pulse width, the power dependence on the detuning of the resonator natural frequency with respect to the transition resonant frequency. The results obtained are in the qualitative and quantitative agreement with the experiment on photoexcited pentacene molecules in p-terphenyl. The article is devoted to 85th birthday of V. A. Atsarkin.