Aromatic polyurea exhibiting large second harmonic generation and UV transparency

Abstract We report a new organic nonlinear optical material consisting of urea moieties in the main polymer backbone. This aromatic polyurea is highly soluble in a variety of solvents and could be cast into flexible, colorless, transparent films. Aromatic polyurea exhibited high thermal stability up to 290 °C. From the Maker fringe measurements, the nonlinear d 33 coefficient of poled polyurea was found to be 14 times that of potassium dihydrogen phosphate (KDP) crystals at 1.064 μm. Aromatic polyurea thin films showed an absorption maximum at 253 nm and transparency down to 307 nm. Aromatic polyurea is the first example of an organic materials to be used as a frequency doubler at fundamental wavelengths as low as 615 nm. A waveguide mode structure consisting of a 0.2477 μm thick polyurea film has also been demonstrated. Interestingly, large second-order optical nonlinearity coupled with unique optical transparency in the UV region make polyurea a potentially useful material for nonlinear optics.