The paper offers a discrete thermodynamic model of lasers. Laser is an open system; its equilibrium is based on a balance of two thermodynamic forces, one related to the incoming pumping power and another to the emitted light. The basic expression for such equilibrium is a logistic map, graphical solutions to which are pitchfork bifurcation diagrams. As pumping force increases, the relative populations on the ground and lasing branches tend to zero and unity correspondingly. An interesting feature of this model is the line spectrum of the up and down transitions between the branches beyond bifurcation point. Even in a simple case of 2-level laser with only 2 possible transition types (up and down), the spectra look like sets of the line packets, starting well before the population inversion. This effect is an independent confirmation of the Einstein's prohibition on practical realization of 2-level laser. Multilevel lasers may be approached by employing the idea of thermodynamic activity for the emitting atoms. Considering coefficient of thermodynamic activity of the lasing level atoms to be proportional to the ratio of life times on the upper and lasing (the 3d) levels, one can derive a new basic map for the multilevel laser system. For a modest ratio only of 0.01, spontaneous transitions between levels are pushed to the area beyond population inversion, opening a space for the functioning of laser.
Discrete Cavity Dynamics in Free-Space Brillouin Laser
Helmholtz-Institut Jena（亥姆霍兹耶拿研究所）；Abbe Center of Photonics, Friedrich Schiller University Jena（弗里德里希·席勒大学耶拿阿贝光子学中心）；Center for Advanced Laser Technology, Hebei University of Technology（河北工业大学先进激光技术研究中心）；Hebei Key Laboratory of Advanced Laser Technology and Equipment（河北省先进激光技术与装备重点实验室）；Collaborative Innovation Center for Diamond Laser Technology and Applications（金刚石激光技术与应用协同创新中心）；Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitat Jena（弗里德里希·席勒大学耶拿理论物理研究所）
Mimicking the earth core conditions with ultrafast laser materials interaction
The Ohio State University（俄亥俄州立大学）；CNRS, Institut d’Optique Grduate School, Laboratoire Hubert Curien UMR 5516, Université Jean Monnet（法国国家科学研究中心，光学研究生院，居里安实验室，圣艾蒂安大学）；Center for Electron Microscopy and Analysis（电子显微镜与分析中心）；Colorado State University（科罗拉多州立大学）；XUV Lasers Inc（XUV激光公司）
