content_image/343528.jpg content_image/343529.jpg content_image/343530.jpg
We also recorded the Mueller matrix of the set up with the glass substrate only. Up to a normalization factor we deduced 

<img src='content_image/343528.jpg'>

which satisfies M glass ≃ I with I the identity matrix. It implies that the optical set up do not induce depolarization and that consequently we can rely on our measurement procedure for obtaining M . 

## VI. APPENDIX C: THEORETICAL MUELLER MATRICES. 

The precise form of the theoretical Mueller matrice M $_{L}$th. deduced from equation (1) is 

<img src='content_image/343529.jpg'>

with M th. 00 = (2 | A | 2 + | B | 2 + | C | $^{2}$) / 2, M th. 01 = Re [ BA ∗ + AC $^{∗}$], M th. 02 = Im [ AB ∗ + CA $^{∗}$], M th. 03 = ( | C | $^{2}$− | B | $^{2}$) / 2, M th. 11 = | A | 2 + Re [ B $^{∗}$C ], M th. 12 = Im [ B $^{∗}$C ], M th. 13 = Re [ AC $^{∗}$− BA $^{∗}$], M th. 22 = | A | $^{2}$− Re [ B $^{∗}$C ], M th. 23 = Re [ CA $^{∗}$− AB $^{∗}$], M th. 33 = (2 | A | $^{2}$− | B | $^{2}$− | C | $^{2}$) / 2. Similar formula are obtained for M $_{R}$th. after permuting B and C . $_{L}$th. 

From the previous relations we deduce the useful equations (valid for M ) 

<img src='content_image/343530.jpg'>

Together with equation (3) equation (6) allow us to fit B/A and C/A if we replace M th. by M $_{L}$exp. (a similar procedure is applicable to M $_{R}$exp. after permuting B and C ). 

