Optical excitation of a half leak guided modes has been used for characterising in detail the optical tenser profile in a homeotropically aligned ferroelectric liquid crystal (SCE8) layer. In the S-A phase it is found, by careful fitting of multilayer Fresnel theory to angle dependent transverse magnetic to transverse electric conversion reflectivity data, that at 1 degrees C above the S-c* to S-A phase transition there is a finite pre-tilt of the S-A layers. Further fitting of similarly recorded data in the S-c* phase gives details of the cone angle and the chiral pitch of the S-c* phase. These results not only serve to obtain material parameters for this S-c* phase but also illustratee fully the enormous potential of the half leaky guided mode technique.