The escape factor in plasma spectroscopy. I - The escape factor defined and evaluated. II - The case of radiative decay. III - Two case studies

In plasma spectroscopy, it is frequently convenient to treat the effect of self-absorption parametrically as a reduction in the spontaneous transition probability by a parameter known in the literature relating to lab studies as the escape factor. In the present paper the concept of the escape factor is developed in a systematic way; a definition is given and the escape factor is evaluated for Gaussian, Lorentzian, and Holtsmarkian profiles, for upper and lower limits to the source function, and for infinite plane-parallel slab and infinite cylinder geometries. In addition, a case study of the escape factor for a source decaying radiatively is presented. This is followed by a discussion of two contrasting approaches to the evaluation of the escape factor.