  Photon channel perspective on high harmonic generation (HHG) is proposed by
quantizing both the driving laser and high harmonics. It is shown that the HHG
yield can be expressed as a sum of the contribution of all the photon channels.
From this perspective, the contribution of a specific photon channel follows a
simple scaling law and the competition between the channels is well
interpreted. Our prediction is shown to be in good agreement with the
simulations by solving the time-dependent Schrodinger equation. It also can
well explains the experimental results of the HHG in the noncollinear two-color
field and bicicular laser field.
