The idea here is that what people generally regard as a "photon" today is actually one second's worth of oscillations of light at a particular frequency. Imagin

The idea here is that what people generally regard as a "photon" today is actually one second's worth of oscillations of light at a particular frequency. Imagine each oscillation of light as the true elementary particle instead. There are plenty of those elementary particles within the classical "photon" that can be split out into smaller "photons" of a different frequency.