Simultaneous measurement of temperature-dependent refractive index and depth-resolved thermal deformation fields inside polymers

Based on phase-contrast spectral optical coherence tomography, a method of simultaneously measuring the temperature-dependent refractive index and depth-resolved thermal deformation field inside polymers is proposed. The interference spectra are acquired before and after the change in the polymer temperature, and the geometrical and optical thickness variations of the polymer are decoded from the spectra. The temperature-induced refractive index change is subsequently estimated using the measured thicknesses variations. With the estimated refractive index change and the phase difference map decoded from the spectra, the depth-resolved thermal deformation field inside the polymer can be evaluated. To validate the method, silicone rubber and epoxy resin films were measured while their temperatures were increased from 50 °C to 100 °C. The measured linear thermal expansion coefficients of the silicone rubber and epoxy resin films were 3.74 × 10−4 and 5.85 × 10−5, respectively, which are close to the existing recommended data. The advantages of the method are that the depth-resolved thermal deformation field inside the polymers can be measured in real time while eliminating the errors caused by changes in both the polymer refractive index and the medium temperature, as well as system vibration.