Resonance Raman scattering of beta-carotene solution excited by visible laser beams into second singlet state

This study aimed to use self-absorption correction to determine the Raman enhancement of beta-carotene. The Raman spectra of beta-carotene solutions were measured using 488 nm, 514 nm, 532 nm and 633 nm laser beams, which exhibited significant resonance Raman (RR) enhancement when the laser energy approaches the electronic transition energy from S-0 to S-2 state. The Raman intensity and the actual resonance Raman gain without self-absorption from S-2 state by beta-carotene were also obtained to evaluate the effect of self-absorption on RR scattering. Moreover, we observed the Raman intensity strength followed the absorption spectra. Our study found that, although 488 nm and 514 nm pumps seemed better for stronger RR enhancement, 532 nm would be the optimum Raman pump laser with moderate RR enhancement due to reduced fluorescence and self-absorption. The 532 nm excitation will be helpful for applying resonance Raman spectroscopy to investigate biological molecules in tissues.