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Ultrafast Measurement Of Two-Photon Absorption By Loss Modulation, Peifang Tian, Warren Warren
Ultrafast Measurement Of Two-Photon Absorption By Loss Modulation, Peifang Tian, Warren Warren
Peifang Tian
We demonstrate a direct and sensitive technique for measuring two-photon absorption (TPA).An intensity- modulated femtosecond laser beam passes through a sample exhibiting TPA.A TPA signal at twice the modulation frequency is then generated and subsequently measured by a lock-in amplifier. The absolute TPA cross section of Rhodamine 6G at 800nm is found to be 15.32.010 -50 cm 4 s / photon and agrees well with previously published results obtained with much higher intensity [J.Chem.Phys. 112, 9201 (2000)]. Our method may be especially useful in measuring nonlinear absorptions of nonfluorescent materials.