Detection of birefringes

Hi again,

a question regarding the sorting of the qs:

Line 504 in 1f62af2

if np.abs(Cp_t1-Cp_t2) > qsd_thr: ## birefringence

this statement is used to detect birefringes for a layer and to decide if eq (13) or (15) is used for qualculation of the Cps.

I am wondering if the birefringes criterium for a single layer can't be done by checking for off-diagonal elements in the Euler-transformed epsilon 3x3 matrix?

in the best case one saves to calculate Cp_t1 and Cp_t2 and it would be also more simple and intuitive in my opinion.

Best

Daniel

I am not 100% sure on this, the way I see it there is an implication but not 100% reciprocity: you need off-diagonal terms in the rotated epsilon tensor to get birefringence, but if by chance these give you degenerate eigenmodes then you want to sort again on the s/p pol. So the first criterion is really the power flow (i.e. the Cps)

Thanks a lot for the clarification. Then I stick with the criterion but will return the result, isBirefringent as output of the method instead of storing it in the layer. This makes also sense as the birefringence/sorting of the layer/qis can be zeta and frequency dependent.