Quantum counter for far-infrared radiation

Two types of three-level quantum counters, based on the Bloembergen and the inverted scheme, are discussed with respect to their application for up-conversion of far-infrared (FIR) radiation to visible light. It is reported on a tunable quantum counter of the inverted type: in optically pumped ruby, photons at 29 cm-1are absorbed by the transitionbar{E}(2E) →2bar{A}(2E) and lead to an increased R2- fluorescence radiation. By Zeeman splitting of the2Elevels, tuning of the detected frequency from 29 cm-1to higher and lower frequencies is possible (with 1 cm-1/Tesla). Using the 891-GHz radiation of an HCN laser we determine for the quantum counter a power conversion efficiency of the order of 10-6and a frequency bandwidth of 360 MHz. We find the interesting result that phonon bottleneck due to resonant trapping of 29 cm-1phonons can lead to an increase of the quantum efficiency by orders of magnitude

First-order phase transitions in outbreaks of co-infectious diseases and the extended general epidemic process

In co-infections, positive feedback between multiple diseases can accelerate outbreaks. In a recent letter Chen, Ghanbarnejad, Cai, and Grassberger (CGCG) introduced a spatially homogeneous mean-field model system for such co-infections, and studied this system numerically with focus on the possible existence of discontinuous phase transitions. We show that their model coincides in mean-field theory with the homogenous limit of the extended general epidemic process (EGEP). Studying the latter analytically, we argue that the discontinuous transition observed by CGCG is basically a spinodal phase transition and not a first-order transition with phase-coexistence. We derive the conditions for this spinodal transition along with predictions for important quantities such as the magnitude of the discontinuity. We also shed light on a true first-order transition with phase-coexistence by discussing the EGEP with spatial inhomogeneities.Comment: 6 pages, 3 figure