thanks for your help so far, is in reflection and a continuous laser, I put a linear polarizer and after it a lambda half plate rotated it, but the dispersion relation did not change, I am not sure if I also have to put something in the detection path?
thanks a lot for your answer, basically I just put a lambda half plate in my excitation path and find the highest/lowest energy dispersion on higher k vectors yes? and nothing in my signal path ?
in my case it is a 1 dimensional ridge GaAs