###
Carrier-envelope phase explained: unitary theory of carrier-envelope
phase effects

Vladimir Roudnev

Consider a quantum system interacting with a short intense linearly polarized laser pulse. Using the two-dimensional time representation and the Floquet representation, a straightforward connection between the laser carrier-envelope phase (CEP) and the wave function is established. This connection is simply a unitary transformation in the space of Floquet components. This approach allows us to interpret any CEP effect as an interference between the Floquet components and to put limits on using the CEP in coherent control. In particular, we discuss the dependence of the CEP effect on the pulse duration. We illustrate the theory with a simple two-level system example.