Photoacoustic observation of third-order absorption in thallium halides at 1.06 µm

1.06 μm laser photoacoustic spectroscopy has been applied to studies of third-order multiphoton absorption in selected thallium halides. This readily detected bandgap crossing absorption is observed at laser fluences significantly below the
n
-on-one damage threshold. Its importance for modeling of high intensity effects in wide bandgap ionic crystals is discussed.