Microscopy

We report nonlinear absorption data of LaF3 and MgF2 single layers at 193 nm. A highly surface sensitive measurement strategy of the laser induced deflection technique is introduced and applied to measure the absorption of highly transparent thin films independently of the substrate absorption. Linear absorptions k ¼ ðα × λÞ=4π of 2 × 10−4 and 8:5 × 10−4 ðLaF3Þ and 1:8 × 10−4 and 6:9 × 10−4 ðMgF2Þ are found. Measured two photon absorption (TPA) coefficients are β ¼ 1 × 10−4 cm=WðLaF3Þ, 1:8 × 10−5, and 5:8 × 10−5 cm=WðMgF2Þ. The TPA coefficients are several orders of magnitude higher than typical values for fluoride single crystals, which is likely to result from sequential two step absorption processes.