High resolution voltage dependent tilt angle studies using optical excitation of half-leaky guided modes have been conducted on a homeotropically aligned ferroelectric liquid crystal mixture (Merck SCE13) in the SAphase. Uniform homeotropic alignment is realised, with no surface aligning layer, by the application of an in-plane DC electric field when the liquid crystal is in the SC* phase. The applied field unwinds the pitch of the SC* chiral helix and gives a uniformly tilted homeotropic monodomain. On warming into the SAphase, detailed studies of the voltage induced tilt, the electroclinic effect, are then conducted at various temperatures. Because there is no influence of surface anchoring forces, the linear relationship between the induced tilt angle and the DC field is obtained even under very weak fields. Further, the relationship between induced tilt and temperature confirms the predictions of a second order Landau mean-field theory with a coupling term between the tilt angle and the DC field.