Two-phonon absorption operator in spectroscopy

► Report of a closed-form expression for the two-particle operator ezaˆ+2 on coherent states. ► ezaˆ+2 operator is effectively a squeezing operator upon acting on coherent states. ► A first-time report is this result ekaˆ+2z=ey2kdidye-y2. ► This result is tested by calculating the electronic dipole-moment-time-correlation function. ► Franck-Condon factors are also reported. Results are identical to those in the literature.