Two photon absorption in PTCDA films using the z-scan technique

The two-photon absorption coefficient of a polycrystalline PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride) thin film was measured at 880 nm using the z-scan technique. The 2 $\mu $m thick PTCDA film was grown by organic molecular beam deposition (OMBD) on Pyrex. For the z-scan measurements $\sim $1 ps pulses were focused onto the thin film using a microscope objective lens (100x) of numerical aperture 0.55 and a beam waist of 1 $\mu $m. The films have been moved by a translation stage with a travel range of 100 $\mu $m and with a step size of 0.5 $\mu $m. The two-photon absorption coefficient of PTCDA obtained from a fit with open aperture measurements at different intensities results to $\sim $100 cm GW$^{-1}$. The z-scan measurements demonstrate that crystalline PTCDA films possess strong nonlinear optical properties that might be utilized for optical applications.