  The Yudin-Ivanov formula [Phys. Rev. A 64, 013409 (2001)] is generalized such
that the most general analytical expression for single-electron spectra, which
includes the dependence on the instantaneous laser phase, is obtained within
the strong field approximation. No assumptions on the momentum of the electron
are made. Previously known formulas for single-electron spectra can be obtained
as approximations to the general formula.
