Abstract

Degenerate four-wave mixing (DFWM) is a standard technique for measuring the nonlinear third-order susceptibility (χ⁽³⁾). In the usual DFWM experiment the modulus of (χ⁽³⁾) is measured. We have used DFWM in the nanosecond regilne to investigate the third-order nonlinear properties of diphenyl polyenes in solution. In these experiments we observe a double-peak structure in the phase conjugate pulse. We have interpreted this structure as the result of a slow grating, induced by two-photon absorption (TPA), superimposed in time on a fast grating.¹ We describe here an analysis of these experimental results, which allows simultaneous measurements of the real and imaginary parts of χ⁽³⁾, i.e., Re[χ⁽³⁾] ∝ n_2, the nonlinear refractive index coefficient, and lm[χ⁽³⁾] ∝ β, the TPA coefficient.

© 1992 Optical Society of America