Is the transmission matrix of a scattering medium a unitary matrix ?

Hi Sanjiv,

In short, no.

The total scattering matrix, composed of the transmission matrices and reflexion matrices from both sides, is unitary if the scattering medium is non-absorbing but the transmission matrix itself, even the complete one, is not.

If the transmission matrix where unitary, that would mean that all the energy you send from one side goes to the other one. This is not possible as a significant part of the light is reflected back.

Best,

Sebastien