In the previous discussion, the radiation propagation in astronomical maser sources was studied assuming that the properties of the pumping process, as summarized by the volume pump rates Pi and loss rates Γi, are given. It is now time to investigate the underlying pumping mechanisms that keep the masers going. This is done in the present chapter, which discusses the various mechanisms that can lead to maser inversion. Most of the information that can be extracted about the physical conditions in maser sources comes from studies of pumping schemes.
KeywordsOptical Depth Brightness Temperature Radiative Pump Pump Rate Escape Probability
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