MEASUREMENTS OF UV 2-PHOTON ABSORPTION RELATIVE TO KNOWN RAMAN CROSS-SECTIONS

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 P+L of two interacting laser beams at P and L is compared to the known stimulated Raman gain at the difference frequency L-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. © 1979 The American Physical Society.