Two-photon absorption (TPA) cross sections of benzene and of three alkali-halide crystals (KI, KBr, RbBr) are reported for a total excitation energy of 6.7 eV. A calibration technique is used whereby the TPA coefficient at the sum frequency ${\omega }_P+{\omega }_L$ of two interacting laser beams at ${\omega }_P$ and ${\omega }_L$ is compared to the known stimulated Raman gain at the difference frequency ${\omega }_L-{\omega }_P$ in the same material, or in other materials. The results, obtained with nsec pulses, are compared to cross sections measured by a psec laser system. A proposal is made for the extension of the present experimental setup, resulting in a significant enhancement is sensitivity and the possible utilization of low-power cw lasers for these measurements.

• Received 16 November 1978

DOI:https://doi.org/10.1103/PhysRevB.19.5388