Polyethylene terephthalate cubic nonlinearity coefficient measurement with a modified Z-scan technique

A modified Z-scan technique was used to measure the polyethylene terephthalate (PET) cubic nonlinearity coefficient n ₂ at two different wavelengths (1030 and 515 nm). The proposed technique was benchmarked with the well-studied fused silica (FS) sample. The obtained n ₂ values for fused silica n ₂(F S,1030n m)=1.72, n ₂(F S,515n m)=3.1 and for PET n ₂(P E T,1030n m)=11.5 in the units of 10^-7 c m ²/G W agree well with the previously published data. The nonlinear coefficient for PET at the wavelength of 515 nm n ₂(P E T,515n m)=26.5⋅10^-7 c m ²/G W was obtained in this work, presumably, for the first time, and demonstrates high nonlinearity of PET in the visible band. The proposed modified Z-scan technique exhibits a factor of three better sensitivity with respect to the traditional one, which was crucial for PET measurements due to its low damage threshold.