Numerical and experimental work is presented to show the effects on the shape, magnitude, and phase of a photothermal deflection (PTD) signal due to changes in the thermophysical properties of the target and deflecting medium, and the distance of the probe beam from the surface. The PTD signals show qualitative agreement with the temperature gradient normal to the surface, calculated with a numerical model. The results also show that a maximum in time-response profile of the PTD signal occurs in certain instances due to asymmetric changes in the temperature field over time. The effect of a changing temperature field on the PTD signal may be used to detect the onset of phase change in a target.