Comparison of experimental and theoretical excited-state spectra for rhodamine 6G

The stimulated emission cross section (σ
e
) and the excited-state absorption cross section (
\sigma*
) for this dye are resolved across the fluorescence and the lowest energy ground-state absorption bands. The absorption is weak (
\sim0.4 \times 10^{16}
cm
²
), particularly at the longer wavelengths [Fig. 3(c)]. Lasing properties are predicted from Fig. 4(b), which shows a plot of the (σ
e
) curve displaced with respect to the S
1
state as the zero-energy level of reference, on top of the long-axis polarized ground-state absorption band. Spectral assignments are proposed in terms of symmetry arguments based on this observation.