Three-photon absorption in a charge transfer compound pumped with picosecond and nanosecond lasers

A new intramolecular charge transfer compound with an absorption band in the short wavelength range has been synthesized. The measured three-photon absorption coefficient and the corresponding molecular cross-section when pumped by a nanosecond beam are gamma = 2.2 x 10(-17) cm(3)/W-2 and sigma(3) = 6.4 x 10(-74) cm(6)/s(2). respectively. When pumped by a picosecond laser beam, the three-photon absorption cross section is one order of magnitude lower. Three-photon-absorption-induced frequency-upconverted fluorescence emission has been observed by pumping with 8 ns 1.06 mum laser pulses. The emission intensity dependence of the incident intensity obeys the cubic law.