天文脉泽和Dicke超辐射
Astronomical masers and Dicke's superradiance
摘要：
本文从麦克斯韦-布洛赫方程出发，研究了粒子数反转气体的辐射性质和辐射过程。我们专注于脉泽行动和迪克的超辐射建立他们的关系，在整个辐射过程中的时间演化的系统作为一个功能的位置。我们表明，脉泽行动和超辐射不是竞争的现象，而是互补的，并定义两个不同的辐射强度的限制。当粒子数反转密度和偏振振幅在时间尺度上的变化长于影响其演化的非相干过程的时间尺度时（例如，碰撞），而超辐射定义了当这些条件逆转时发生的快速瞬态状态。我们展示了如何从脉泽制度的超辐射的过渡将发生每当达到临界阈值的列密度的粒子数反转，在这一点上建立了一个强有力的相干性水平的系统和一个强大的辐射突发可以在瞬态制度。这个临界水平也决定了从不饱和脉泽制度过渡到饱和脉泽制度的空间区域，因此超辐射可以被看作是两者之间的中介。我们还量化了相对于两个脉泽制度的超辐射阶段期间获得的辐射强度的增益，并展示了超辐射期间的强相干水平如何很好地适合解释揭示脉泽托管区域中强烈和快速辐射耀斑的观测结果。
英文摘要：
We consider the radiation properties and processes of a gas with a population inversion using the formalism based on the Maxwell-Bloch equations. We focus on the maser action and Dicke's superradiance to establish their relationship in the overall radiation process during the temporal evolution of the system as a function of position. We show that the maser action and superradiance are not competing phenomena but are rather complementary, and define two distinct limits for the intensity of radiation. Masers characterise the quasi-steady state limit, when the population inversion density and the polarisation amplitude vary on time-scales longer than those of non-coherent processes affecting their evolution (e.g., collisions), while superradiance defines the fast transient regime taking place when these conditions are reversed. We show how a transition from a maser regime to superradiance will take place whenever a critical threshold for the column density of the population inversion is reached, at which point a strong level of coherence is established in the system and a powerful burst of radiation can ensue during the transient regime. This critical level also determines the spatial region where a transition from the unsaturated to the saturated maser regimes will take place; superradiance can thus be seen as the intermediary between the two. We also quantify the gain in radiation intensity attained during the superradiance phase relative to the two maser regimes, and show how the strong coherence level during superradiance is well suited to explain observations that reveal intense and fast radiation flares in maser-hosting regions.
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