  The optical conductivity of a polaronic charge carrier in the intermediate
and strong-coupling regimes is calculated for a tight-binding electron using
exact diagonalization. Two different simple models of the electron-phonon
coupling are considered: the Holstein model, with coupling of the lattice
displacement to the local electron density, and the Su-Schrieffer-Heeger type
of coupling arising from modulation of the electronic overlap integral. The two
models are shown to exhibit a similar polaronic absorption band. However, the
Su-Schrieefer-Heeger form of coupling gives rise to a second strong absorption
band not present in the Holstein model. This additional feature corresponds to
transitions from the ground state of bonding character on a shortened bond to
excited states of anti-bonding character on the same shortened bond.
