Mitigation of stimulated Raman amplification artifact in transient absorption spectroscopy

Abstract

Artifacts due to nonlinear optical processes like "Cross Phase Modulation (XPM)", "Stimulated Raman Amplification (SRA)", and "Two-Photon Absorption (TPA)" etc., have a detrimental effect on Transient Absorption Spectroscopy (TAS). In this study, we investigate the transient response of distilled water to explore the nature of SRA artifacts. The supercontinuum probe, generated in a sapphire crystal pumped by 808 nm, 50 fs laser pulse, is approximated as a linearly chirped Gaussian with a chirp parameter of 36. The chirp in the probe affects the TAS data, because the different spectral components of the probe arrive at different times, even at zero delay. The process of eliminating the effect of this chirp on the TAS data is successfully implemented. The method presented here will be useful to correct the dynamics of several processes of light-matter interactions such as coherence phenomena, electron-electron scattering and electron-phonon scattering. Also, the imaginary part of the third-order nonlinear susceptibility (χIm ) of water is extracted to be 2.088 × 10 −23 m 2 /V 2 , using the SRA artifacts.