We have performed the first experiment on the free-electron laser (CLIO) at the Laboratoire pour l'Utilisation du Rayonnement Électromagnétique (LURE). In a transmission experiment we observed strong power limiting at wavelengths longer than the absorption edge associated with induced free carrier absorption produced by direct interband two-photon transitions in InSb. We have estimated the two-photon absorption (TPA) coefficient (β) of InSb at 8.9 μm to be 2 cm MW-1, by fitting the power-limiting effect with a simple theoretical model. An important feature of this result is that we are utilizing the broad tunability of the FEL to explore the TPA theory to shorter wavelengths than hitherto available with CO2lasers. The result is in broad agreement with the longer-wavelength measurements of Sheik-Bahaeet
展开▼
