Attosecond laser pulse synthesis using bichromatic high-order harmonic generation

We analyze the dynamical symmetries and the selection rules relevant to the process of production of high-order harmonics as a result of irradiating an atom with strong, continuous bichromatic laser radiation of similar frequencies omega and omega+delta omega. We show that when the two laser frequencies are close to one another (small delta omega), the spectrum becomes very dense and new selection rules are obtained. Such a dense spectrum of harmonics could be a source for the production of attosecond light pulses. We demonstrate our results numerically on a one-dimensional model Hamiltonian of a Xe atom and show how a pulse of length 700-as could be produced.