Thickness determination with chemical identification of double-layered polymeric thin film by using multiplex CARS

By utilizing characteristic Coherent anti-Stokes Raman Scattering (CARS) spectra from different organic polymers of polystyrene (PS) and polymethylmethacrylate (PMMA) coated on the glass substrate, we have determined the thickness of double-layered polymer as well as their chemical identification. We have also discussed about the effects of nonlinear optical interaction between third-order optical susceptibility of neighbored polymer films on the overall CARS signal. The two polymers exhibit very close C–H vibration modes as well as refractive indices, but the dependence of each resonant CARS signal component on focal depth is successively identified with the theoretical description of CARS field.