Abstract

Different classes of organic compounds and polymers are currently being intensively studied in an effort to identify materials with large third-order nonlinearity (χ³) for various switching applications. Direct measurement of intensity-dependent total transmission of ultrashort laser pulses is one of the many ways of measuring the imaginary part of χ³-However, intensity-dependent transmission of laser beams can arise not only from (single-photon nonresonant) two-photon absorption, which is characterized by the two-photon absorption coefficient β, but also from excited-state absorption, which is characterized by the absorption cross section σ. We were able to differentiate between the two processes, and determine the values of β, σ and τ, the decay time for the excited state, by measuring the intensity dependence of transmission of the materials for laser beams of different pulsewidths. We also measured the real part of χ³ of the materials using the Optical Kerr Gate technique.

© 1992 IQEC