Tracking coherent low frequency vibrational information of Rh101 in ground and excited electronic states by broadband transient grating spectroscopy

Time- and frequency-resolved broadband transient grating (BB-TG) spectroscopy is used to distinguish between ground- and excite-electronic state vibrational coherence at different wavelengths. Qualitative theoretical analysis using double-sided Feynman diagrams indicates that a superposition of ground and excited state vibrational coherence are contained in the ground state absorption (GSA) and stimulated emission (SE) overlap band, while only the excited state is contained in the excited state absorption (ESA) band. The TG experiment, in which a white light continuum (WLC) is adopted as a probe, is conducted with rhodamine101 (Rh101⁺) as the target molecule. Fourier analysis of TG dynamics in a positive delay time range at specific wavelengths enables us to distinguish the low-frequency vibrational modes of Rh101 in ground- and excite-electronic states.