Calibration of hydrogen atoms measurement using femtosecond two-photon laser induced fluorescence

Abstract

A new calibration method for H-fs-TALIF is proposed, and the ratio of two-photon absorption cross-sections, $\sigma^{(2)}$, for atomic hydrogen (H) and krypton (Kr) is determined for the broadband emission of a femtosecond laser system. The estimated ratio of the two-photon absorption cross-sections for H and Kr is $\sigma^{(2)}$ for H and Kr $\sigma^{(2)}$(Kr)/$\sigma^{(2)}$(H) = $0.027\pm 20$%, which is nearly twenty times lower than values previously obtained with narrowband nanosecond lasers. This discrepancy highlights the need for independent calibration of TALIF measurements for a specific laser pulsewidth range.