Phase sensitive OCT enables the measurement of thermal expansion in laser irradiated material at high lateral and temporal resolution. In principle, a calculation of the 3D temperature distribution and its temporal evolution should be possible by evaluating the local expansion. This could be utilized for a non-invasive and very fast temperature measurement, e.g. to realize an online dosimetry for photocoagulation. The possibilities of quantitative investigations at high axial and lateral resolution are demonstrated by imaging the reversible thermal expansion in laser irradiated multilayer silicone phantoms.