A fluorescence-based method to measure an absolute two-photon emission cross section is reported in which we measured the absolute fluorescence power using a commercial luminance meter. An analytical expression between the average fluorescence power and the average pump power is derived. The expression is valid for any arbitrary-shaped pump-laser profile. It was also found that the origin of deviation of fluorescence intensity from expected quadratic dependence on pump power is thermal in nature. The method is used to measure the absolute two-photon-excited (TPE) emission cross section of Rhodamine 6G at an 800-nm excitation wavelength. The measured TPE emission cross section at 800 nm is η δ=(36±6)× 10<sup>−50</sup> (cm<sup>4</sup>/s)/photon. Within experimental error, the result obtained with this method is quite close to the previously reported TPE cross section obtained with the fluorescence method.
© 2003 Optical Society of America
(190.4180) Nonlinear optics : Multiphoton processes
(190.4710) Nonlinear optics : Optical nonlinearities in organic materials
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6410) Spectroscopy : Spectroscopy, multiphoton
Rakesh Kapoor, Christopher S. Friend, and Amitava Patra, "Two-photon-excited absolute emission cross-sectional measurements calibrated with a luminance meter," J. Opt. Soc. Am. B 20, 1550-1554 (2003)