AROMATIC POLYUREA EXHIBITING LARGE 2ND-HARMONIC GENERATION AND UV TRANSPARENCY

We report a new organic nonlinear optical material consisting of urea moieties in the main polymer backbone. This aromatic polyurea is highl y soluble in a variety of solvents and could be cast into flexible, co lorless, transparent films. Aromatic polyurea exhibited high thermal s tability up to 290-degrees-C. From the Maker fringe measurements, the nonlinear d33 coefficient of poled polyurea was found to be 14 times t hat of potassium dihydrogen phosphate (KDP) crystals at 1.064 mum. Aro matic polyurea thin films showed an absorption maximum at 253 nm and t ransparency down to 307 nm. Aromatic polyurea is the first example of an organic material to be used as a frequency doubler at fundamental w avelengths as low as 615 nm. A waveguide mode structure consisting of a 0.2477 mum thick polyurea film has also been demonstrated. Interesti ngly, large second-order optical nonlinearity coupled with unique opti cal transparency in the UV region make polyurea a potentially useful m aterial for nonlinear optics.