Picosecond z-scan measurements of the two-photon absorption in beta-carotene solution over the 590-790 nm wavelength range

The two-photon absorption (TPA) properties of beta-carotene (beta-carotene) in chloroform solution were investigated over the 590-790 nm wavelength range. The TPA was characterized using the open-aperture z-scan technique with picosecond pulses provided by a widely traveling-wave optical parametric amplifier (OPA) pumped with a Ti:sapphire laser amplifier. We found the 0.2-1 cm/GW values of two photon absorption coefficient in the 725-790 nm wavelength region. At shorter wavelengths, a dramatic increase in the two-photon absorption around 600 nm was observed. The observed two photon absorption dependence on the excitation wavelength can be explained by the onset of strong excitation from the ground state 1A(g) to the higher lying two-photon allowed m(2)A(g) band centered around 310 nm (similar to 4 eV).