Scattering matrix Transmission Matrix lasers
Apparently, these matrices are difficult to measure in the optical domain, that's why there is not much information on them, especially very little easy-to-understand references. However I have found one paper, which is short and very practical and therefore easy to read: Measuring the Transmission Matrix in Optics: An Approach to the Study and Control
of Light Propagation in Disordered Media, PRL 104, 100601 (2010). 

UPDATE: And a nice, though a bit longer, paper on scattering matrices in lasers: Scattering matrix analysis of a triangular ring laser, JLT 12, 202 (1994).

The following is apparently the first use of the scattering matrix for lasers: Studies of semiconductor lasers of the interferometric and ring types, IEEE JQE 18, 610 (1982).