Hi. I'm trying to model the attenuation (extinction) of a weak laser through a gas sample using the Beer-Lambert law. I've found that the attenuation cross section can be written as the sum of both a scattering and absorption cross section, however I'm having difficulty finding a source that lists equations for both of those. One book I keep seeing referenced, and have been using myself is Loudon's "The Quantum Theory of Light" . He gives a lot of information, but it's confusing me a little bit. In chapter 2 he lists an equation for an attenuation coefficient, and then in chapter 8 he lists the same equation and calls it the Elastic Raleigh scattering cross section. I haven't seen any mention of an absorption cross section anywhere, so I was wondering where that would fit in to this model.