We demonstrate a scheme for efficient coherent anti-Stokes Raman scattering (CARS) microscopy free of nonresonant background. Our method is based on a compact Er:fiber laser source. Impulsive excitation of molecular resonances is achieved by an $11\mathrm{fs}$ pulse at $1210\mathrm{nm}$ . Broadband excitation gives access to molecular resonances from $0{\mathrm{cm}}^{-1}$ up to $4000{\mathrm{cm}}^{-1}$ . Time-delayed narrowband probing at $775\mathrm{nm}$ enables sensitive and high-speed spectral detection of the CARS signal free of nonresonant background with a resolution of $10{\mathrm{cm}}^{-1}$ .