3. Results and discussions
3.1. Linear absorption spectra
Fig. 1 shows the linear absorption spectra of the two fluorine derivatives in DMF. The two compounds both show strong UV absorption in the spectral ranges of 320–480 nm for A and 300–460 nm for B, which both correspond to molecular ground state one-photon absorption with the cross-section as high as 10−14 cm2, and no linear absorption in the spectral range of 500–1200 nm. The three-photon energy of 1064 nm laser just falls into the strong UV absorption region and there were no absorption at the two-photon energy (532 nm) for the two compounds, which meet the conditions of 3PA. Consequently, three-photon absorption in the two solutions may be anticipated at 1064 nm.