Three-photon absorption of radiation from a Ti:sapphire laser by methylstyrylbenzene

It is shown that 2,2'-di-methylstyrylbenzene (bis-MSB) at a concentration of 10^-3 M in 1-methyl-2-pyrrolidone can fluoresce at 420 nm upon excitation by a 708-nm femtosecond Ti:sapphire laser. The dependence of the fluorescence intensity on the excitation power proved to be cubic. The three-photon absorption cross section of bis-MSB was estimated as (1.61 ± 0.10) × 10^-79 см⁶·с²·фот^-2 bis-MSB is recommended as a cubic standard to normalise laser powers in three-photon measurements.