According to Ref.  (page 27), ‘the correct expressions for the and .. were first obtained by Lavrovskaya et al.’ ). Since the explicit expressions (without walk-off) for the ssf and sff cases are given in Ref. , we first check the expressions above to see if we obtain the same results.
For crystals belonging to point group mm2, there are 5 non-zero d coefficients: d15, d24, d31, d32 and d33. For a Type I (ssf) interaction, deff(ω1) is obtained from Table 3.3 as: