Photoacoustic determination of three-photon-absorption cross sections in thallium halides at 106 μm

A calibration technique is described and employed for the photoacoustic measurement of three-photon absorption in TIBr and TIClBr at 1.06 μm. The generalized three-photon-absorption cross sections are found to be σ(3) = (9 ± 7) × 10−81 cm6 sec2 in TlClBr and σ(3) = (7 ± 6) × 10−82 cm6 sec2 in TlBr. The possibility of using the laser-power dependence of the photoacoustic signal to differentiate between the impact-ionization avalanche and multiphoton-polaron mechanisms of optical dielectric breakdown is also discussed. To date, we have seen no evidence of the behavior predicted by the avalanche model.