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We report on the generation of narrow-bandwidth and frequency-modulated cascaded emission of two photons from a collimated Yb atomic beam. Efficient population transfer from the ground state (6s2 1S0) to upper state (6s7s 1S0), of which direct transition at 291.1 nm is dipole forbidden, is achieved through a resonant two-photon excitation enhanced by the electromagnetically induced transparency mediated by the intermediate state (6s6p 1P1). Then cascaded emission of two photons with a bandwidth of 54 MHz at 611.3 nm (idler) and 555.8 nm (signal) occurs in sequence from the upper state via the spin triplet state (6s2 3P1). Numerical calculations of the density matrix equations taking into account the residual Doppler effect and strong driving fields successfully explain the experimental results for the idler and signal beam intensities depending on the various parameters of the driving fields. Synchronized optical switching and frequency-modulation characteristics of the idler and signal beams are also reported. [ABSTRACT FROM AUTHOR]