Pulse poling of high performance nonlinear chromophores in polymers

Conjugated chromophores with permanent dipole moments can be aligned by heating a thin polymer film containing chromophores in an external electric field. The heated "guest-host" system is then cooled in the field to maintain the chromophores' alignment. Dielectric breakdown and charge transfer, however, often limit the external electric field to about 100 V/μm of film thickness. It was hypothesized that electrical pulses could increase the voltage of the poling field without damaging the sample films. This was achieved by combining an amplified waveform from a function generator with the DC poling field. Pulse amplitudes were varied from 10 to 103 V. Pulse frequencies were varied from 10-1 to 103 Hz with a duty cycle of up to 50% of the pulse period. Pulse amplitudes were found to have optimum effects at less than 15% of the DC field at low frequencies, 0.1-10 Hz, with a sinusoidal pulse shape. It was found that this technique induced up to a 20% improvement in optical properties without damaging the sample films.