Abstract

The sign and the magnitude of both the real and the imaginary part of the third-order optical nonlinear susceptibility χ³ at 532 nm in polythiophene (PT) thin films has been determined by the Z-scan method. Both the real part of χ³_{532 nm} (-6.1 × 10^-9 esu) and the imaginary part of χ³_{532 nm} (-1.9 × 10^-9 esu) are shown to be negative. Strong saturation absorption effects in PT at 532 nm have been observed from open aperture measurements. The results show that the nonlinear response in the single photon π–π^* transition band in polythiophene thin films is dominated by absorption saturation.

© 1991 Optical Society of America