Three-photon excitation of p-quaterphenyl with a mode-locked femtosecond Ti:sapphire laser

Ignacy Gryczynski, Henryk Malak, Joseph R. Lakowicz

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6 Scopus citations


We observed emission from p-quaterphenyl (p-QT) at 360 nm when exposed to the focused light from a femtosecond (fs) Ti:sapphire laser at 850 nm. This wavelength is too long to allow two-photon excitation of p-QT. The emission intensity of p-QT was found to depend on the cube of the laser power at 850 nm, suggesting that excitation occurs due to a three-photon process. The same emission spectrum and single exponential decay times were observed for three-photon excitation at 850 nm as for two-photon excitation at 586 nm and for one-photon excitation at 283 nm. The same rotational correlation times were observed for one-, two-, and three-photon excitation, but higher time-zero anisotropies were observed for two- and three-photon excitation. The steady-state anisotropies for one-, two-, and three-photon excitation are precisely consistent with cos2θ, cos4θ, and cos6θ excitation photoselection, where θ angle between the electric field of the incident light and the absorption dipole. These experiments were performed with 3 × 10-5 M solutions of p-QT. Use of such low concentrations was possible because p-QT displays one of the highest apparent cross sections we have observed to date for three-photon excitation. The spatial distribution of the excited fluorescence was less for three-photon excitation than for two-photon excitation of Coumarin 102 at the same 850-nm excitation wavelength. The high cross section, photostability, and clear cos6θ photoselection of p-QT make it an ideal three-photon standard for spectroscopy and microscopy.

Original languageEnglish
Pages (from-to)139-145
Number of pages7
JournalJournal of Fluorescence
Issue number3
StatePublished - 1 Jan 1996


  • Frequency domain
  • Three-photon excitation
  • Ti:sapphire laser
  • Time-resolved anisotropy
  • Two-photon excitation


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