Erratum: Complete Mueller matrix from a partial polarimetry experiment: the nine-element case (J. Opt. Soc. Am. A (2019) 36 (403) DOI: 10.1364/JOSAA.36.000403)

In the definition of the covariance matrix given by Eq. (3) of [1], the second Pauli matrix sj in the Kronecker product must be complex conjugated. However, the explicit form of the covariance matrix reported in the same equation is correct. The quantities E1 through E4 entering Eq. (4) must not be squared, in agreement with their definition in Eq. (2). In Appendix B, Eqs. (B7a) and (B7b), the matrix element M22 must actually be M12, as evident from Eqs. (B5a) and (B5b). More importantly, besides the condition given by Eq. (B9), the additional condition must be used in order to find the actual solutions in the special case of completing the Mueller matrix of a retarder, i.e., a matrix having strictly zero first row and column (except for the leading element M11). Being partially based on the results from Appendix B, Appendix C is also affected by the above condition. Note however that experimental Mueller matrices never have strictly zero first rows and columns because of measurement noise so that the use of condition (B10) is superfluous in practical applications.