Saturation absorption and Kerr susceptibility in polydiacetylene Langmuir-Blodgett film.

Direct measurements of the saturation absorption from Langmuir- Blodgett films of a polydiacetylene have been carried out in picosecond time domain. Using a photoacoustic technique, we have obtained directly the imaginary part of Kerr susceptibility, x sup (3) (-omega,omega,omega,-omega). The magnitude of x sup (3) is found to be in excess of 10 sup (-8) e.s.u., and the associated ground state recovery time is less than the laser pulse width of 3 ps. These results are discussed in terms of phase space filling model for a one-dimensional exciton.