Hello, iam new to polariton lasing and have to hold a speech about it. So ive got some questions and it would be great if someone could answer them. In a polariton laser, lower polaritons form a quasi bose einstein condensat at k=0. [My most important question:] I dont get it when the coherent photons are emitted (what process actually causes this). Why are the photons conherent? Is there some kind of chain reaction involved (does the emission of photons cause other photons to emit)? Would polariton lasing be possible without the bottleneck in the dispersion relation? Could it be possible to build a exciton laser this way (why it have to be polaritons?)? At high polariton densitys (caused through high pumping energy or?) the polariton laser becomes a photon laser. What causes the emission of coherent photons in this case? Does the polaritons still exist in this regime? I often read about stimulated and spontaneous scattering. Stimulated scattering occurs if the final state (k=0) is populated. In case of two polariton scattering, is there a need of population of the final state of the idler polariton? What is spontaneous scattering? Could someone name some applications of polariton lasers?