[VARR-11b]
F. Varray, A. Ramalli, C. Cachard, P. Tortoli, and O. Basset,
"Fundamental and second-harmonic ultrasound field computation of inhomogeneous nonlinear medium with a generalized angular spectrum method",
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, vol. 58, no. 7, pp. 1366-1376, 2011

.